Observing satellites

The full name of this site is “Satellite Observation: Observing Earth Observation satellites”. Usually, it is meant figuratively: the articles deal with the technical, commercial or political aspects of earth observation, not with advice about how to literally observe satellites. So for this article, let’s do exactly that instead. Let’s look at how artificial satellites can be seen and imaged.

One of the main reasons for looking into this is that it is a fun and relatively easy thing to do for amateur astronomers: it does not require a lot of expensive hardware, and it can be done even from extremely light-polluted areas. The other reason is that it is exactly the opposite of observing the Earth from a satellite: from a physics point of view it is very similar, so it gives a good overview of the challenges of Earth observation. In fact, it is even used to test satellites on the ground, by making them image satellites on orbit. So it can also give a hands-on experience and understanding in optics and imaging, which can be applied to Earth observation later.

European ATV resupply vehicle, imaged from the ground by the German TIRA radar

The first thing to know about imaging satellites from the ground it that is quite hard: satellites are on a strict schedule, they move fast, and they are small, far-away objects. However, with a little bit of preparation, these challenges can be overcome. This article will go into the details of these challenges:

I. Scheduling an observation

  1. Orbital Mechanics
  2. Illumination
  3. Clouds

II. Dealing with the movement of the satellite in the sky

  1. Fixed pointing
  2. Manual tracking
  3. Motorized tracking
  4. The special case of GEO satellites

III. Getting details on small objects, a more technical part to give basic notions of optics and imaging

  1. Diffraction
  2. Sampling
  3. Noise
  4. Turbulence
  5. Shutter mode

IV. A cost-effective imaging system for the ISS

V. Conclusion

Arguably the best image of the ISS ever taken from the ground

I. Scheduling an observation

Orbital mechanics

The strict schedule of satellites makes them a very occasional target: because of orbital mechanics, low Earth Orbit satellites pass over an observation site at precise times, and the rest of the time they are below the horizon, so they are not visible. These pass times can be found on websites like n2yo,  or the orbital elements of a satellite can be downloaded from the US Strategic Command, Celestrak or even Mike McCants’s website if you are interested in Western spy satellites. Once you have the orbital elements, software like heavensat or JSatTrack can give you the pass times, and nice visualization of the orbits and of the geometry of the observation.

Several factors affect pass times: the inclination of the satellite’s orbit, for instance, makes it visible only to observers located at a lower latitude than the inclination. The height of the orbit also has an impact: a satellite flying low over the Earth’s surface will appear to be close to the horizon during most passes, making it hard to image. On the contrary, a high-flying satellites will often pass almost at the vertical of the observer, making it easier to observe. Finally, the type of the orbit also has a role to play: most Earth Observation satellites are on a sun-synchronous orbit (SSO), meaning they pass over a given site at always the same local time. By contrast, the International Space Station is not on a SSO, so the time it passes overhead changes each day.

Interface of HeavenSat, showing the orbit of the ISS, with the part that is in sunlight in yellow. It also shows which parts of the Earth are in daylight.


Once the list of pass times is available, the scheduling is not done yet: some passes are not exploitable due to illumination constraints. For an observer to see a satellite with the naked eye, the observer has to be in the dark, but the satellite has to be in sunlight. This means only passes shortly after sunset, or just before sunrise, are interesting. During those times, it is night-time for the observer so the sky is dark, and stars and satellites are visible. However, since the satellite is at higher altitude than the observer, it is already in daylight and so the light it reflects can be seen by the observer. Unfortunately, this makes observing SSO satellites very difficult: they usually pass at around local midnight and noon, which means either both the satellite and the observer are in sunlight, or none of them are.  The orbit of the ISS makes it much easier to observe, especially around May:

For a few days each May, the orbital plane of the International Space Station closely follows Earth’s day-night terminator, which keeps the spacecraft in near-constant sunlight. (From http://www.skyandtelescope.com/observing/celestial-objects-to-watch/space-station-frenzy/)


Finally, the weather usually plays tricks on observers: check the skys are clear before scheduling an observation, especially if there is a lot of hardware to setup.

These orbital mechanics, illumination and weather constraints are similar the the ones experienced by observation satellites imaging the ground: they can only do so at one point of their orbit, need the ground to be in sunlight (except for radar and infrared sensors), and need clear weather (except for radar sensors).

II. Dealing with movement

Even when a good pass can be found, the apparent movement of the satellite in the sky makes it hard to image. The first thing to do is to make a naked eye observation, or to use binoculars. This way, the pass prediction method can be checked, and it gives a first view of the object, its brightness and its velocity in the sky. The first naked-eye observation of the ISS (we will come back to it a lot) is an especially beautiful sight, as it is very bright.

This long-exposure photograph gives an impression of what a pass of the ISS in a very dark sky looks like.

This first pass, and the others that follow, will be a few minutes long at most for LEO satellites.  In that short time, the satellite will rise from the horizon, pass directly overhead if the pass is well-chosen, and then sink to the opposite horizon. If the pass is not optimal, the satellite will rise to a lower elevation angle (directly overhead is 90° elevation). At maximum elevation, the satellite appears to move the fastest and thus is harder to follow through binoculars or any other instrument.

Ground track of the ISS. The circle is the region from which it is visible. Ticks indicate its position at different times.

So in order to image the satellite with a camera for instance, the movement has to be dealt with. There are several ways to do this:

Fixed Pointing

This is just pointing the instrument in a fixed direction and taking pictures during the short moment the satellite is in the field of view. In order to take high-resolution pictures of a satellite, a high level of zoom has to be used on the camera, which usually means the field of view is very small. So the camera has to be very precisely pointed, and the images taken at exactly the right moment. This will usually result in few images, and because the satellite is moving, it will appear blurry if a long exposure time is used. If short exposures are used, the quantity of light received by the camera will be limited, which means the image will be noisy with most cameras. Although this type of pointing is used by satellites to image the Earth (most point their telescope in one fixed direction and let the Earth drift in their field of view), they can get away with it because they have a specialized system (called Time-Delay Integration) in their sensors, which eliminates the motion blur even with long exposure times. General-use cameras and sensors do not have this, so the movement has to be compensated with another method.

In first-order approximation, Time-Delay Integration (TDI) moves the pixels inside the camera to compensate for object movement

Fixed-pointing imaging also can be done with wide field of view cameras, in order to detect satellites in low Earth orbit and find their precise orbit. This is done for instance by the members of the Seesat-L network, who keep track of Western spy satellites that way. They even have a nice webpage explaining how to observe and compute the orbits yourself, and giving advice on how to  to observations. They use images like the one below by Marco Langbroek (Source), and with accurate timekeeping and multiple observations they can accurately predict the orbits and the following passes of those satellites.

Long-exposure image of a US Keyhole spy satellite, by Marco Langbroek.

Manual tracking

This means the observer keeps the objective or the telescope pointed at the satellite, and thus the satellites remains in the field of view of the sensor for a long time. That way more images are acquired, hopefully with less motion blur, and without adding any tracking hardware to the instrument. This method is especially useful when imaging satellites with a Dobsonian telescope as this type of telescope is fully manually operated. With a little bit of training and the aid of a smaller spotting scope mounted on the main telescope, the telescope can be kept pointed on the satellites with relatively high accuracy.

A simple, 400$ Dobsonian telescope with an aperture of 8 inches

However, keeping the object perfectly still in the field of view is impossible so the exposure time has to be kept relatively short. This also helps reduce the impact of the vibrations caused by moving the telescope around. Note that from the point of view of an Earth Observation satellite, vibrations are also an issue. They can occur, for instance, when the satellite is quickly repointed to image two areas of the ground in quick succession, and that is why these satellites must have rigid telescopes, which keep their shape in spite of accelerations, and must have pointing motors which cause a minimum of vibrations. The great advantage of manual tracking is that because the object stays in the field of view for a long time, many images can be acquired. Martin Lewis has a great tutorial on how to image the ISS with manual tracking and a Dobsonian telescope, with all the details on acquisition setup and image processing.

Image of the ISS taken with the 8″ Dobson above, a high-speed monochrome camera and manual tracking.

Motorized tracking

This requires that the camera or telescope is mounted on a motorized mount, and that a computer sends precise instructions to those motors to track the satellite, using its orbital elements for instance. This kind of system requires dedicated hardware, usually with a wide field of view telescope to acquire the target and keep the main, narrow field of view telescope pointed on it. Thierry Legault and Emmmanuel Rietsch have developed such a system, to keep a large 14-inches telescope continuously pointed at satellite. It gives great images of the Shuttle, the ISS and even individual astronauts. It even gives good images of spy satellites. Legault’s images are widely recognized as among best amateur images of the ISS, with Alessandro Bianconi being a close contender, apparently also with a 14″ telescope.

International Space Station 2016-06-15 UT19.26, Alessandro Bianconi

Others have set up similar automatic tracking systems:

Automatic systems can keep the object almost perfectly centered in the field of view, which allows the use of very narrow field of view systems, and also eliminate the motion blur. A good system can also reduce vibrations in the telescope by using smooth movements for tracking, which is hard to do with a manual system. The downside of those systems is that they require a guiding mount with strong motors, which is not cheap. They also seems to require a PhD in robotics or electronics to be set up, which is a lot to ask. Nevertheless, it is the solution used by professionals, such as the Russian Altay Optic-Laser Center or the USAF’s Starfire telescope, to image satellites.  Those professional systems also use adaptive optics to compensate for the turbulence of the atmosphere (more details on that in the next part), which is unfortunately out of the price range of amateur observers.

Seasat imaged by the Starfire 3.5m telescope. (A. without adaptive optics. B. with adaptive optics. C. with additional post-processing)

Professional telescopes look like this, a far cry from the 400$ Dobson seen above:

Lacrosse-5, imaged by the Altay Optical Center

Radar can also be used to image satellites, using the same method as the Synthetic Aperture Radar (SAR) satellites. The ATV image at the top of this article was produced using a Germany SAR-Lupe satellite from the ground to image space. Germany also has a dedicated ground-based radar for satellite imaging, called TIRA (Tracking and Imaging RAdar). It produces very nice images:

The Space Shuttle imaged by TIRA


The special case of GEO satellites

Satellites in geostationary orbit are an exception: since they appear fixed in the sky, a fixed pointing with an extremely long exposure time can be used. This allows for amazing videos such as this one (view in full-screen and look for the stationary dots in the top half):

Marco Langbroek also has great images of the Geostationary belt such as the one below, taken with a DSLR camera, which enable him to locate and identify high-orbiting satellites, even the classified ones:

NSA spy satellite PAN located in the GEO belt, close to civilian communication satellites and to the French Syracuse 3A military communications satellite.

Jannne from r/astrophotography has also produced this wonderful image:

And has a labeled version with the names of the satellites.

III. Getting details on small objects

Satellites can be quite large, from a few meters to a hundred of meter for the ISS, but they orbit far away, at least 200km up. Consequently, they appear very small to an observer on the ground. To the naked eye, they are a small dot. With binoculars, this small dot can turn into a small square for the ISS, but details are hard to see. In order to get a photograph with small details, a few things have to be overcome

The diffraction limit

Physics is a harsh mistress and places a strict limit on what level of details an optical instrument can give. Basically, even a perfect telescope does not give a perfectly sharp image. There is always some amount of blur which is introduced by the instrument. This blur is called the Airy disk. For a perfect telescope, this amount of blur depends only on the size of the opening of the telescope (called its aperture). A telescope with a twice larger diameter will produce twice sharper images.

As the aperture increases, images look better and sharper

So in order to get fine details, a telescope with a large aperture is required. That is why no post-processing tricks can make an image taken with a consumer camera look as sharp and detailed as one taken by a large telescope.  The diffraction limit places constraints on the optical part of the instrument: a given size is required to reach a certain level of sharpness. But it is not enough to reach sharp images. The electronic sensor of the instrument has to be carefully chosen too, because of physical limitations.


In a digital optical instrument, light from an object is taken up by the aperture, concentrated and magnified by the optics, and then projected onto a sensor chip. This chip is made of a array of pixels. Each pixel measures the quantity of light falling on it, and outputs a number based on this.

A digital sensor turns the light that falls onto it, which can have any shape, into a grid of numbers.

A digital image on the web or on your computer is just these numbers, displayed on a grid. Ideally, we would use infinitely small pixels, to get maximum details. However, this is not possible: pixels have to be manufacturable so they have a minimum size. As can be seen in the image above, pixel size has an impact on the image: details smaller than the pixel size are destroyed: in the digital image, all that remains are squares of the size of the pixel, with varying intensity. The curves of the circles have turned into blocky shapes. This seems to be a problem, but recall that in a real telescope, diffraction already introduces a blur in the image. This means the small details have already been blurred out, so there is no point using a pixel smaller than the smallest details remaining in the image. So the right size of the pixel depends on the size of the Airy disk on the sensor, which in turns depends on the aperture and on something called the focal length of the telescope, which describes how much it magnifies images.

Impact of focal length on magnification. The higher the focal length, the smaller the field of view (AFOV), but the larger the images appear on the sensor. (h is the physical size of the sensor)

The exact right ratio of the pixel size compared to the Airy disk is determined by the Nyquist criteria, displayed below:


In practice for amateurs, the available pixel sizes are constrained by what is manufactured by by sensor producers like Sony or Nikon, so one has to play with the focal length of the telescope to reach the Nyquist criteria. Designers of Earth observation satellites can order tailor-made sensors, so they choose the focal length so that the telescope is maximally compact and as sharp as diffraction allows, and adjust pixel size in function.


Noise is something we want to get rid of in images: it can make them aesthetically unappealing, or it can even hide important content if there is too much of it. That is why sensor manufacturers keep improving their technology, to remove it and make better images. Unfortunately, they can only deal with the noise that comes from the sensor itself, the electronic noise. Some sensors are so good they have virtually no electronic noise, but they still do not produce noise-free images. This is because light itself has noise.

In the quantum mechanics point of view, light is made of small particles called photons. Photons come in discrete numbers: there can be 0, 1, 2, 3, … photons, but not half a photon. So when the level only light is very low, when for instance, each pixel of a sensor receives half a photon on average, this means that some of the pixels receive 0 photons, some receive 1, of few of them receive 2, etc… This creates noise in the image because even though the signal should be uniform, quantum mechanics says it is not. This is called quantum noise, photon noise or shot noise.

The impact of quantum noise at low light levels. Light levels increases from left to right and from top to bottom. From wikipedia.

The only way to get around quantum noise is to gather more light. There are several ways of doing this: increasing the aperture of the instrument -which comes at an exponential cost in optics-, increasing the interval of time the sensor receives light (the exposure time), which can create motion blur if the object moves, or taking many images with a short exposure time and adding them digitally (called stacking). The interest of stacking is that because it is a digital process, the position of the object in each image can be measured, and its movement compensated in post-processing. So it digitally creates a long exposure time, while not adding motion blur, which is very powerful. However, to make good use of it, the sensor has to be able to take many images per second, which puts constraints on the electronics of the sensor and on the downstream image transfer, storage and processing.

Noise is also a concern for satellites observing the ground: that is why they use TDI, which is a kind of image stacking done directly in the sensor.

Another impact of noise is that because the more photons the sensor receives, the less noise there is, a good instrument should not lose photons before they are converted to an electrical signal in the sensor. This is measured by the Quantum Efficiency of the instrument, which is ideally close to 100%, i.e. all photons are converted to a digital signal.


The air in the atmosphere is never completely still and uniform. Because of this, it deflects light rays and degrades the quality of telescope images by introducing additional blurring. This mostly concerns telescopes imaging from the ground towards the sky, because they are closer to the atmosphere so its effect is amplified. The impact of turbulence on the image is to add a blur which changes shape around 10 times per second, making it hard to compensate. It also impacts large telescope more strongly: At a scale of up to around 20 cm, the atmosphere is roughly constant and uniform, but at larger scales, it gets chaotic. This means small telescopes can almost always get as good images as the diffraction limits allows. Large telescopes however will get lucky sometimes and image up to their diffraction limit, but most of the time they will get images as sharp as a 20cm telescope. This is why large modern observatories have complex adaptive optics systems to compensate for the turbulence: otherwise, their very large mirrors would give them the sharpness of a much smaller telescope.

Image of a single star, with a small turbulence blur. The ring structure is what remains of the Airy disk

This means that most of the time and without adaptive optics, apertures larger than 20cm are not effective to increase sharpness, and only help in gathering more photons to reduce noise. However, if the sensor acquires images at least 10 times per second, it will sometimes capture an image in which the atmosphere was perfectly still and introduced no blur, making full use of the large aperture. This is called lucky imaging. Those lucky shots become less and less common as the aperture increases, so this method does not fully trump turbulence.

Telescopes in space and imaging space, like Hubble, are not affected by the atmosphere though, and do not need to compensate for it. That is why some optical telescopes are still sent to space to do astronomy, especially for wide field of view imaging, where adaptive optics no longer work.

Shutter mode

Since with fixed pointing or with manual tracking the sensor will image objects with a lot of movement, it should not distort the shape of moving objects. This means the sensor should expose all its pixels at the same time. Otherwise distortions can occur, which make it harder to stack images:

Rolling shutter distortion. This occurs because with rolling shutter, all pixels are not read at the same time.

So a sensor with a global shutter should be preferred. It has to be noted that at least one type of Earth observation satellites is using sensors with global shutter, and not TDI: the Skysats from Skybox are using 2D-sensors with global shutter. They take a series of image of the same scene, and then stack them to reduce noise.

Other considerations regarding the optical design of the telescope can be taken into account: a telescope with mirrors will have less light distortion than one with lenses, a compact, thermally stable, rigid design should be preferred to reduce vibrations, and because we want to image with a relatively large field of view, the image should be sharp all over the sensor. These aspects require a deep dive into telescope design though, so for now they will be ignored.

IV. A cost-effective imaging system for the ISS

In the previous section, we saw the various drivers of image quality in an optical instrument. From them, an effective and cheap way of getting high-resolution images of the ISS can be derived.

  1. Motorized tracking is expensive and complex, so do not use it.
  2. Fixed pointing offers only a very short time to image objects at high magnification, so use manual tracking.
  3. Aperture should be as big as possible, but the bigger it is the more expensive the instrument, and above 10-20cm (depending on the location), atmospheric turbulence limits its impact. So a 10-20cm aperture telescope is a good way to go.
  4. 10-20cm aperture and manual tracking orient us towards a 4-8″ dobsonian telescope (price range 200-400$).
  5. A small finder scope to be fixed on the Dobson will help keep the ISS in the field of view.
  6. Regarding the sensor, it should be as high-speed as possible, with as many pixels as possible. It should output unprocessed pixels, as video compression can destroy the details on small, moving objects. Modern sensors provide pixel rates designed to saturate the widely available interfaces like USB3, so there is no easy way to cheaply get more pixels. They also have low electronic noise. A stand-alone sensor with a global shutter and an saturating the USB3 interface will to the job. The Sony Exmor IMX174 sensor is a good fit.
  7. Because of the pixel size of the sensor and the focal length of the telescope have already been chosen, an optical device called a barlow lens might be needed, to increase the focal length and reach the Nyquist criteria.
  8. Because the sensor outputs a lot of pixels that need to be stored for post-processing, it needs to be hooked to a computer with a high-speed storage drive, so a laptop with a SSD and USB3 is better. The other option is to to pre-processing on the fly during the acquisition to only keep the interesting part of the image and write only this to disk. The laptop is required for its portability.

If you already own the laptop, the total budget is around 1000€. Some parts can be replaced with cheaper alternatives: a DSLR or a smartphone could be used instead of the camera and the laptop, although with no guarantees on the results.

This kind of setup gives good results. This stacked and post-processed photo was done with a 8″ Orion XT8, an ASI 174MM camera, a 3x Barlow lens, a 6×50 finder scope and a laptop with USB3 and a Samsung 850 EVO SSD:

The post-processing was done with PIPP to resize the images and compensate the movement of the ISS, then the stacking, digital sharpening and zoom was done with Registax 6.

The different modules of the ISS can be seen, even the Progress resupply vessel:


Similar setups give also very nice results, such as this colour gif by Silwyna posted on r/astrophotography :

A simple DLSR camera with a long-focal-length objective can also give interesting results, although with less details.

Other objects than the ISS can be imaged, but the ISS is the largest and most impressive: the next biggest objects are the Chinese space station Tiangong 1 and 2, but they are much smaller, as can be seen in these amazing composites by Philip Smith and Mariano Ribas:


The Chinese are planning a larger space station that will be more interesting to image. The Space Shuttle used to be a nice subject, as can be seen in Legault’s images, but it does not fly anymore. As for actually observing Earth Observation satellites, it is possible to try with the recommended setup but because they are even smaller, to get interesting images a larger telescope than a simple 8″ Dobson is required. Legault, using his 14″ motorized system, has very nice images of spy satellites, of an interplanetary probe, and of the Dragon and ATV resupply vehicles:

V. Conclusion

Imaging artificial satellites, and imaging the Earth from a satellite are very similar tasks. Regarding image acquisition, orbital mechanics, sunlight and cloud cover apply equal constraints on both. The physical laws on the propagation of light impose the same limits on the level of details on both, and although the optics and electronics used in an amateur telescope are orders of magnitude cheaper than those used in an Earth observation satellite, they are based on the same core technology.  However,  it is hard to find a satellite to play with, whereas taking pictures with a basic telescope is in reach of many, and is a great way to get acquainted with the same basic topics. It also opens the door to visual astronomy, which offers amazing sights of the planets.

On a final note, taking pictures of a satellite is possible not only from the ground, but also from another satellite, but that will probably be the subject of another article.

iss pleiades
The ISS, probably imaged from a Pléiades satellite

Smallsat constellations

In the article on Persistent Surveillance, I described the options for keeping a constant, 24/7 watch on a location though the use of high-altitude satellites. Those options are all expensive and technically risky. However, as hinted at in the article, there is a more straightforward way to achieve same goal, or at least to come reasonably close: using a constellation of many satellites in Low Earth Orbit (LEO).

Such a constellation gives a high revisit: while with a limited number of satellites, it may not be able to provide an uninterrupted video stream of a place, it can take snapshots of it every few minutes. With more satellites, a truly persistent stream might be achievable.

An example of such a constellation is the one planned by BlackSky Global. The full constellation is to include 60 spacecraft on low-inclination orbits, in order to provide high revisit over the most populated areas of the globe:

Data from a BlackSky presentation. Note the red band around 45°N

The full constellation would give a revisit every 18 minutes over the USA, Europe and Northern China. It would be made of 10 orbital planes:

BlackSky ground tracks

Phonesats and cubesats

However, in order for it to be affordable, not only have the launch costs to be low, but also each individual satellite has to be relatively cheap. Clearly, using traditional earth observation satellites, which are priced at a few hundred million dollars a piece, is not an option.

The solution is first to fly low-altitude orbits. This is because for a given ground resolution, the diameter of the telescope carried by the satellites is proportional to the altitude of the orbit, and larger telescopes cost much more than small ones. However the atmosphere drags down satellites that fly too low, so the minimum practical altitude is around 400km for satellites without dedicated drag-compensating engines. This puts metric resolution in reach of 30cm-diameter telescopes.

Secondly, since smaller telescopes can be used, the idea is to also lower the cost and size of the rest of the satellite by using miniaturized off-the-shelf components, derived from consumer electronics, wherever possible. Planets Labs pushed this idea to its logical conclusion: after its founders launched smartphones in space to check they would work on orbit, they designed cubesats based on the same technology and with small telescopes to take pictures from orbit. These very small satellites, measuring 10cm x 10cm x 30cm, are able to take 3m resolution images, on the cheap, by leveraging the peace dividends of the smartphones wars.

Planet has launched several batches of Doves, as they call them, and each batch is a new iteration of the concept, bringing improvements and resolving issues identified on orbit. Each batch has tens of satellites, and the end goal of Planet is to have hundreds of satellites in the air, continuously replaced as they become obsolete and fall down to the Earth. This will allow them to provide daily revisit of all of the globe at medium resolution. This is not extremely high revisit, but it is extremely high coverage. Since this coverage is systematic, it allows to perform untargeted searches: an user can look at the daily evolution of any place, even in the past since the imagery has already been collected. This is not possible with traditional observation satellites which have to be manually tasked to look at a specific place.

Concept of the Planet constellation

Small satellites

Other companies are looking into intermediate size satellites, halfway between Doves and the traditional 1 tonne satellites. Skybox, for instance, has launched several 100 kg satellites, called SkySats, which provide a resolution slightly better than 1m. This is highly competitive with the established players in commercial satellite imaging: Airbus’ sharpest satellites, for instance, produce only 70cm resolution data. The Skybox solution offers a similar resolution, at a lower cost and a potentially higher revisit rate. Furthermore, Skybox satellites use a specific sensor setup that can take full-motion videos, something the traditional satellites cannot do.

The BlackSky constellation mentioned above would also be made of similar satellites, weighing around 100kg and with a better than 1m resolution. UrtheCast is planning a combined optical and radar constellation, to be built by SSTL. The Chinese are also interested in small satellites for Earth observation and have launched some.

These constellations of high-resolution satellites do not provide a daily coverage of the whole Earth like the Doves do, but if fully implemented they do provide high revisit rates, with revisits every few minutes, and reasonably high resolutions. This makes them interesting for intelligence and military applications, as the SEEME project by the US Department of Defense shows.

They also have an interesting synergy with Doves-like constellations, and that is why Planet just bought Skybox: since the Doves image the whole globe every day at medium resolution, they can detect places where interesting activity is occurring, and then the higher-resolution satellites can be tasked to take pictures of these places, to precisely characterize this activity. Because the volume of data produced by the Doves each day is extremely high, only a fraction of it can be reviewed by humans. This is why Planet will probably implement automatic change detection and tasking. That way, an algorithm will detect the areas of interest in the Dove imagery, and then order a SkySat to take a picture. The value of that is that if a customer is interested in this area later, he can directly download the high resolution images since they have already been acquired, instead of having to manually task a high-resolution satellite after the fact. So for the customer, high resolution is available everywhere he wants to look, even in the past, because it has already been collected by the tasking algorithm.

In some sense, the medium resolution imagery provides peripheral vision to the high-resolution satellites, much in the same way human vision works: only a tiny part of the eye is capable of high resolution, but since that part is pointed at the interesting details, it gives the illusion of high resolution in all the field of view. This idea of combining a medium and a high resolution constellation is not specific to Planet alone: it is also what Digital Globe wants to do with the Scout constellation. BlackSky, on the other hand, is looking into integrating news feed and social media with satellite imagery, and could deploy an algorithm tasking a satellite based on these in the near future.

However, one of the main limitations of small satellite constellations is that since the satellites have limited agility, if there are many areas to image, and if these areas are in the same region and close to each other, each satellite cannot take pictures of all of them. That means that some satellites have to be tasked to some of the areas of interest, and others the the rest of the areas. This cuts down the revisit rate in the region. Consequently, such constellations can provide an almost persistent surveillance of places spread out all over the world, but when there is a crisis in a region, they cannot perform as well: they cannot provide persistent coverage over all the region at the same time. So they cannot fully replace a fleet of surveillance drones focused on one region in particular, but they can help maintain an up-to-date global picture.

What is the rest of the industry doing?

A OneWeb satellite

One other interesting feature of the current space industry is that smallsat constellations are becoming popular in the communication sector too: Iridium is currently launching its 2nd-generation constellation, SpaceX is thinking about launching several thousands of LEO communication satellites, and OneWeb is securing funds for a similar constellation. The OneWeb project is the most interesting because it has attracted several billions in financing, and a partnership with Airbus to build a new factory to mass-produce small satellites. This factory is set to produce 700 satellites, weighing 150kg each, for half a million dollar a piece. After the OneWeb production run, Airbus is even considering using the same low-cost platform for Earth observation, and sees the US government as a potential customer.

The launcher side of the industry is evolving too: Europe has recently introduced the Vega rocket to launch small payloads to LEO, OneWeb plans to use the Launcher One rocket from Virgin Galactic to replace failing satellites, Planet is scheduled to launch its next satellites on the Electron rocket from Rocket Labs, and SpaceX sees the reusability of its Falcon 9 rocket as a way to launch its potential constellation cheaply and quickly. The Chinese are also introducing small launchers, to be able to orbit payloads on short notice. So the cost of a dedicated launch for a batch of small satellites is coming down across the board, and the rideshare opportunities make it even cheaper to launch prototypes in orbit to validate their performance.


Overall, constellations of small satellites are the best way forward to get high revisit rates: they have no technical risk, are relatively cheap, and can still provide submetric resolution. The combination of a global coverage, medium-resolution component with a higher-resolution system also gives them the ability to act as a highly responsive, uncued search system. Along with lower launch costs, this ensures they will play a big role in the future of Earth observation.

A new German space policy?

German media recently reported the country will procure a new high-resolution optical satellite. According to the press, this satellite will be operated by the BND, Germany’s foreign intelligence service. Such a purchase breaks from the German tradition of operating only radar satellites, under the control of the military, and thus marks an unexpected shift in Berlin’s national security and space policies. To understand its implications better, let’s look a bit more into the details.

The proposed BND satellite is estimated to cost 400M€ and to be launched in 2022. The press mentions that this program is part of a major expansion of Germany’s domestic and foreign intelligence budgets, and is a way to reduce reliance on the United States. It also links it to the late HiROS (High Resolution Optical Satellite) program, that the BND unsuccessfully tried for years to get financed, before it was definitively cancelled around 2012.

HiROS constellation (from 2012 DLR presentation)

HiROS was to be a triplet of 0.5m resolution optical satellites, with 0.8m mirrors. Each of the agile satellites would have had a 12km swath from a 490km orbit. Optionally, they could have carried a 5m resolution thermal infrared imager, and could have used a geostationary data relay satellite to receive their programming and downlink their images in near real-time. On the political side, HiROS was to be used in very close cooperation with the Americans (possibly supplying images to Digital Globe), as numerous leaked US diplomatic cables show.

SAR vs optical market shares (from eijournal.com)

The HiROS project also aimed at building up a purely German industrial base for optical observation satellites: In Europe, the French have been and arguably still are the leaders in optical earth observation, with Germany and Italy specializing in radar satellites (see History of the French reconnaissance system for details). However, high-resolution radar imagery has proven to be a much more limited market than optical imagery, as can be seen in the graph above, and consequently a pivot to optical is very attractive from an industrial and commercial point of view. To this end, DLR, the German Space agency, has been developing the building blocks of high-performance optical satellites. For instance, it provided the optical and infrared focal planes, and the video processing electronics of the Korean Kompsat 3 and 3A satellites (which provide 0.5m resolution from a 528km orbit). Following this industrial objective, HiROS would have been built by the 100% German OHB company, and not by a division of the French-German Airbus conglomerate.

The DLR-built focal plane of Kompsat 3

Moreover, although Germany and France have a sharing agreement of optical and infrared data provided by French spy satellites, the BND wanted to be independent of the French. The German Ministry of Defence apparently did not share the same view. The German government was at the time in talks with the French about sharing data from CSO, the future French optical reconnaissance system. Eventually after the cooperation seemed almost dead, Germany surprisingly agreed in 2015 to fund two thirds of a CSO satellite to the tune of 200M€, with no industrial return in exchange. Presumably, this gives Germany access to around 20% of the CSO output, which will comprise hundreds of 20 to 30cm resolution optical images as well as infrared imagery, starting from 2018. France was strongly opposed to the HiROS program, as it viewed it as a threat to cooperation on CSO.

Consequently, the purchase of an additional optical (and presumably infrared too since the BND was interested in this capability for HiROS) satellite seems to be redundant with buying stakes in CSO: CSO will offer high-revisit, extremely high resolution capabilities that the German system will not be able to match entirely. However, the industrial policy outlined above, as well as the desire to own an independent, sovereign reconnaissance capability explain part of the decision. Organizational and also purely technical points might explain the rest.

On the organizational side, Germany already owns reconnaissance satellites, but these satellites are operated by the German military, not by the BND. In an ideal world, this would not cause any frictions, but the BND may want its own capabilities, to keep its areas of interest secret and to have access to more images. Rivalry between the military and the intelligence services was a major feature of the early history of the US reconnaissance program, and could also be at play here.

On the technical side, the existing German satellite are radar (SAR) satellites: the current SAR-Lupe system has 5 satellites, with at least a 50cm resolution, built by OHB and launched between 2006 and 2008. The program cost was 350M€. It will be replaced by the SARah system around 2018, which will also be a constellation of SAR satellites: a big one with a phased array will be built mainly by Airbus for 350M€, and the other two will be derivative of SAR-Lupe built by OHB. The overall cost is estimated at 800M€.

SAR technology offers several advantages over optical systems: it can see through clouds and at night, the latter being possible with infrared optical systems, but at a lower resolution. It can also see metallic objects very well. Overall, this makes for a responsive system which can guarantee the coverage of an area every day, which is useful from a military point of view: it can and will detect movements of armored vehicles reliably for instance. However, SAR images are very noisy and much harder to interpret than optical images. That means that even with a high resolution, their value for intelligence can be limited. This is supported by the market shares shown above -most commercial customers prefer optical over SAR- and by DLR work on fusing SAR and EO data to fully exploit the potential of SAR. Besides, optical infrared imagery can provide information SAR cannot, such as the heat output of a facility. This might be useful to counter nuclear proliferation for instance: the activity of reactors and enrichment centers can be assessed, and an order of magnitude of their production derived.

High-resolution SAR images. It is clear some training is required to identify objects.

All in all, one might speculate that the interest of the BND in optical systems is due to the fact that they could be more useful for long-term, political and strategic intelligence, whereas SAR systems could be have an advantage for operational military intelligence. An illustration of the difference between the two can be found in the recent annexation of Crimea by Russia: while knowing troop positions in Ukraine might be interesting to German authorities, knowing the intent behind the movements, and the corresponding political objectives, could be even more useful and allow to anticipate events instead of reacting. In the challenging security landscape around the Mediterranean and Russia, anticipation may prove essential, and maybe optical systems serve it better than radar.

In conclusion, the German reconnaissance system is undergoing major changes. In the 2006-2016 decade, it consisted of one constellation of radar satellites operated by the military, for a cost of 350M€. In the next decade, it will be made out of a expanded radar system worth 800M€, an optical satellite operated by the foreign intelligence service worth 400M€, and a 200M€ share in the French optical system. In total, that’s 1.4B€, a fourfold increase over the previous spending level. Such a budgetary efforts, along with the diversification of capabilities and the new role of the BND as a satellite operator, signal that Berlin has acknowledged its strategic environment is uncertain, and that it needs more intelligence to better navigate future crises and to be a major actor in its own security and that of Europe.


History of the French reconnaissance system

France currently has a vigorous earth observation industry, which captures a large part of the export market for reconnaissance satellites. It has not always been this way: contrary to the USA or the USSR, France has never had film-return optical satellites, and orbited its own space reconnaissance systems roughly 30 years later than them. In the same way a previous post on the History of the US reconnaissance system recounted the difficult start and the successes of the American efforts, this post aims to do the same for the French ones. However, it will encompass both optical and electronic reconnaissance, thanks to the lower level of secrecy and the more limited number of systems involved.

A comparative look at both programs shows many common traits: space reconnaissance took quite some time to go from the first studies to the first system on orbit, in no small part due to institutional issues. The coexistence and sometimes competition of satellites with other alternatives, such as planes, is also shared, as well as the issues with the dissemination of highly classified satellite imagery.

Nevertheless, there are peculiarities to the French program: it relies significantly on cooperation with other European nations, which adds its share of organizational difficulties. As mentioned above, it is also much less secret, to the point that reconnaissance satellites are actually exported to many countries. These sales, along with key dates concerning the space-based intelligence systems, their alternatives on the ground and in the air, and the organizations using them, are listed below:


France detonates its first atomic bomb. This test is part of a major effort to build a nuclear deterrent aimed at the USSR. It is also a way to reduce reliance on the USA and support an independent foreign policy. Over the next decades, France builds up a nuclear triad of bombers, submarines and land-based missiles.


• CNES (“Centre National d’Études Spatiales”, National Space Studies Center), is created. It is tasked with coordinating France’s space program.
DMA (“Délégation Ministérielle à l’Armement”, Ministerial Delegation for Armament) is founded. It put in charge of specifying and procuring the systems for the nuclear deterrent.


France starts studies on a film readout reconnaissance satellite called VSOP (“Véhicule Spatial d’Observation Photographique).


Astérix, the first French satellite, is put into orbit by the Diamant launcher. This makes France the third country to launch a satellite. The launch site is in Algeria, which recently gained its independence.  A French satellite is also orbited by an American launcher.


As part of its national independence policy, President De Gaulle withdraws France from the NATO integrated military command. US bases in France are removed. France however remains part of North Atlantic Treaty, which provides for mutual assistance between Western countries.


The launch base of Kourou, in French Guyana, is inaugurated with the launch of a Veronique sounding rocket. It replaces the Algerian launch site.


The Mirage IV supersonic nuclear bomber is modified to carry a reconnaissance pod instead of a bomb. Combined with the C-135 tankers bought from the USA, this gives the French a long-range reconnaissance capability.


• Reconnaissance satellite mockups are on display at the Paris Airshow.
• The French government starts the development of a launch vehicle able to carry these satellites to orbit. CNES leads the program, but it is realized in cooperation with other European countries. The program is eventually named Ariane.


Symphonie, a joint French-German geostationary communication satellite, is launched by an American rocket, on the condition that it will not be used for commercial applications.


• The French Ministry of Defence launches preliminary studies on a optical  mapping and reconnaissance satellite, called SAMRO (“SAtellite Militaire de Reconnaissance Optique”), with a 10m resolution. The main objectives are to increase independence from US intelligence, and to help with nuclear targeting, especially as the French deterrent is considering aiming at economic and military targets instead of population centers. Another objective to monitor Soviet Anti-Ballistics Missile sites around Moscow and Saint-Petersburg, in order to evaluate the impact on the French nuclear deterrent.
• DMA changes its name to DGA (Délégation Générale à l’Armement). Over the years its powers expand to managing procurement for all the armed forces, nuclear and conventional.
• The DC-8 Sarigue, a civilian plane modified to carry out strategic electronic reconnaissance, enters service.


CNES starts working on a civilian optical earth observation satellite called Spot (“Système Probatoire d’Observation de la Terre”,  Demonstration Earth Observation System).


First launch of an Ariane 1 rocket from Kourou. It gives Europe an independent access to space, ending the reliance on the USA. Several versions of Ariane will fly over the years.


• France cancels SAMRO: intelligence on the Soviet ABMs has been acquired by other means, the conventional forces are not interested in its applications due to the low resolution but fear its budgetary impact, and even some part of the strategic forces have reservations. The military decides to provide funds to the Spot program instead.
• The French foreign intelligence service changes its name to DGSE (“Direction Générale de la Sécurité Extérieure”, General Directorate for External Security)
• An image interpretation center is set up to exploit Landsat images.


France tries to convince Federal Germany to restart the SAMRO project together, but the effort fails: Germany does not posses a nuclear deterrent to be concerned about, and is much more interested in monitoring Warsaw Pact troop movements near its eastern border. Due to the significant cloud cover over this region, it favours a radar or infrared satellite able to pierce through bad weather, which the French solution is unable to do.


Spot 1. The two rectangular telescope apertures are visible.

Spot 1 is launched. From a 800km orbit, it offers a 10m resolution in the panchromatic band, and 20m in colour. At the time, it is the highest available on the commercial market, beating Landsat by a wide margin. Shortly after launch, Spot 1 provides images of the Chernobyl accident, showing the destroyed reactor.
• Following the bombing of an air base in Northern Chad, a Mirage IV is sent to assess the results. The 11 hour-mission also involves 4 tankers, which refueled the Mirage 12 times in total, demonstrating the logistical difficulties of long-range reconnaissance with planes.


The military reconnaissance program is resurrected under the new name of Helios, after French political authorities decide to reduce their dependence on US imagery. The military still lacks enthusiasm about the project, but the first Spot images have raised its interest. Italy joins the program as a minor partner, later followed by Spain.


• The first of two Transall Gabriel electronic intelligence planes is commissioned and performs its first mission over Berlin.
• Fall of the Berlin Wall.


Spot 2 is launched. It has the same performance as Spot 1.
• Germany is reunified.


First Gulf War. Spot 1 and 2 are used by French planners to map the region, locate Iraqi facilities and perform bomb damage assessment after air strikes, demonstrating the usefulness of satellite imagery. This is greatly facilitated by the desert terrain, and the rigid organisation and low mobility of the Iraqi army. The French realize they need to reorganize their intelligence methods.


The DRM (“Direction du Renseignement Militaire,” Military Intelligence Directorate), is created by integrating together the intelligence offices of the navy, army, air force and joint chiefs. It is tasked with collecting, analyzing and disseminating military intelligence to the armed forces and political authorities. In time, it will be given tasking authority over military observation satellites, along with DGSE.


Spot 3 is launched. It has the same performance as SPOT 1 and 2.


Helios 1. Note the large aperture of the telescope.

Helios 1 A is launched on a 700km orbit. It is based on a Spot satellite bus but carries a much larger telescope able of collecting panchromatic images with a resolution around 1m.
• Bosnian War. The rough terrain, cloud cover and camouflage techniques of the Bosnian army severely limits the use of satellite imagery, even with the added capabilities of Helios 1 A.
Cerise, a small electronic intelligence satellite, is launched. It is aimed a demonstrating the feasibility of collecting radio and radar signal from space. After one year on orbit, an impact with a debris from the Spot 1 launch makes it lose its attitude control.


The Mirage IV are relieved from the nuclear alert mission. A handful of them are kept and transferred to a strategic reconnaissance squadron. Tactical reconnaissance is performed with more traditional fighter jets.


Spot 4 is launched. It has the same resolution as the previous models, but adds infrared spectral bands and a laser communication terminal. Swath width is 60km for each of the two telescopes.
Horus, a joint French-German Synthetic Aperture Radar (SAR) satellite project, is cancelled.
• The French transport ship Bougainville is converted to collect electronic intelligence.


Helios 1 B is launched. Helios images, which were reserved for strategic applications and consequently had very limited diffusion, start to be used for operational and tactical applications.
Clementine is launched along with Helios 1 B, to replace the failed Cerise satellite.


France and Italy sign the Torino accords. Under the agreement, France will share the future Pleiades high-resolution optical images and Italy the Cosmo-Skymed SAR images. Each countries is given tasking authority of the other’s satellites, for a limited number of images each day.

From left to right: Spot 2,3 4 and 5

Spot 5 is launched. Resolution is markedly improved, reaching 2.5m. Spot 5 also carries a high resolution stereo mapping instrument with a 10m resolution and a 120km swath. It is used by the armed forces to generate  3D digital terrain models, to guide cruise missiles for instance.
• France and Germany sign the Schwerin accords, an image-sharing and satellite tasking agreement. France will provide optical and infrared images from the Helios 2 system and Germany SAR images from the SAR-Lupe constellation.


Second Gulf War. Based on intelligence provided by the Helios satellites and by Mirage IV overflights, the French government decides not to take part in it, and even opposes an United Nations resolution supporting the intervention.


Helios 2. The big square aperture is the VHR instrument, the rectangular aperture is the wide field of view instrument.

Helios 2 A is launched. It carries a Very High Resolution (VHR) instrument, which provides optical images with a resolution around 0.35m and also produces thermal infrared images, enabling it to take pictures at night. This instrument was built by Thales Alenia Space (TAS). It also carries a wide field of view instrument derived from Spot 5, to provide context to the VHR images. Thanks to the contribution of other countries to the programme, Helios 2 images are availabe to Italy, Spain , Belgium, Germany and Greece, as well as to the European Union Satellite Center.
Essaim, a constellation of 4 micro-satellites flying in formation, is launched. The system collects and locates electromagnetic emitters, in a manner similar to the American NOSS satellites.
• The Airbus-built Formosat 2 optical satellite is launched and handed over to the Republic of China (Taiwan). It is the first successful export of a reconnaissance satellite by the French industry. It has a 2m resolution.
• The second and last DC-8 Sarigue is withdrawn from service, due to the high maintenance costs.


The Mirage IV is withdrawn from service.


• The first of 5 German  SAR-Lupe satellites is launched. It has a 50cm resolution.
• The Bougainville electronic intelligence ship is replaced by the Dupuy-de-Lôme, specifically built for this task.


The first of 4 Italian Cosmo-Skymed SAR satellites is launched. It has a resolution of at least 1m.


• France starts working on a follow-on system to Helios 2, as a part of MUSIS (Multinational Space-based Imaging System). The goal is to develop a federated European reconnaissance system, which will integrate the future optical and radar satellite from France, Germany, Italy and Spain.
• The THEOS reconnaissance satellite is launched and delivered to Thailand. It is built by Airbus and has a 2m resolution.


Helios 2 B is launched.


The Reco-NG pod.

• The French Joint Space Command (“Commandement Interarmées de l’Espace”) is created. It does not directly control space assets, but is in charge of long-term planning and coordination on space affairs within the armed forces, with international partners, and with CNES and DGA, the defence procurement organization.
• The Airbus-built Alsat 2A satellite is launched  and delivered to Algeria. It has a 2.5m resolution.
• The Reco-NG airbone reconnaissance pod is accepted in service. It is carried by the Rafale fighter jet and digitally captures visible and infrared images, from very low to very high altitudes. It has a radio downlink capability to shorten the image exploitation time.


Pleiades 1A is launched. Pleiades is a dual use program: most of the images are sold by Airbus on the commercial market, but the French and Italian Ministries of Defence have a daily image quota reserved for them. Pleiades produces 70cm images, and its main feature is its high agility: the satellite can quickly rotate on itself to image different locations successively. This increases the revisit frequency, especially in regions where there are many interesting places to image. The bus is built by Airbus and the instrument by TAS.
ELISA, a successor to ESSAIM, is launched. It also consists of 4 micro-satellites flying in formation.
• After the MUSIS project has been all but cancelled due to diplomatic and budgetary difficulties, France decides to build its follow-on optical system on its own and calls it CSO (“Composante Spatiale Optique”, Optical Space Component). The system will have a Very High Resolution (VHR) satellite on a 800km orbit and an Extremely High Resolution (EHR) satellite on a 480km orbit. The VHR component will probably have a resolution of 35cm, comparable to Helios 2, and the EHR a resolution around 20cm. A third satellite was planned, to increase revisit, but the budget did not allow it. The satellites will be identical and have a thermal infrared capability like Helios 2, and a high agility like the Pleiades satellites. TAS will build the optics and Airbus the bus.
• France, along with the US, the UK and other European and Arab countries, intervenes in the Libyan civil war to support the rebellion. It is the first French conflict in which satellite imaging is truly integrated in the operational loop. The lack of agility of the Helios 2 satellites turns out to be an issue.
• The Airbus-built SSOT satellite is launched and delivered to Chile. It has a 1.5m resolution.


Spot 6

Pleiades 1B is launched, in the same orbital plane as Pleiades 1A. This enables 1-day revisit of any point of the Earth.
Spot 6 is launched. It is a radical departure from the previous Spot architecture. First of all, it is wholly financed and owned by Airbus, whereas previously CNES funded the developments and held shares of the company that commercializes the images. It also does away with the legacy Spot bus and optics, replacing them with a Pleiades-derived high agility bus and higher resolution telescopes. The swath width stays at 60km but the resolution is consequently improved to 1.5m.


• The Airbus-built VNREDSat-1 satellite is launched  and delivered to Vietnam. It has a 2.5m resolution.
• France intervenes in Mali to stop the advance of radical groups on the capital. A ground operation is launched to secure the towns in Northern Mali, and destroy the radical bases. The theater of operations is a desert roughly the size of Texas, and images from the Pléiades satellites proves very useful to build a picture of the situation.


The Spot family

Spot 7, an identical copy of Spot 6, is launched. Shortly afterwards, is is sold to Azerbaijan and renamed Azersky, but Airbus continues to commercialize its images.
• The Airbus-built KazEOsat-1 satellite is launched  and delivered to Kazakhstan. It based on the Pleiades bus and has a 1m resolution.
• CNES starts working on OTOS, a follow-on program to Pleiades, with Airbus and TAS as industrial partners.


After extended negotiations with Germany, it agrees to finance two thirds (200M€) of the third CSO satellite in exchange of tasking rights, without any involvement of the German industry in building the satellite. A mutual tasking agreement, comprising the future German SAR satellites, is put in place.
Sweden is also part of the program and will provide a polar ground station, enabling command upload and image download at each orbit. This will greatly improve the timeliness of the information produced, and consequently make more useful in military operations.


• The Airbus-built PeruSat-1 satellite is launched  and delivered to Peru. It has a 0.7m resolution.
Alsat 2B, a copy of Alsat 2A, is launched. It is still built by Airbus, with a contribution from Algerian engineers. The resolution is 2.5m.
• Planned launch of the Turkish Göktürk- 1 satellite, an optical satellite with a resolution under 0.8m built mainly by TAS.
• By that date, the French Minstry of Defence acquires 120 satellite images per day, mainly from Pléiades.


• Tentative launch of the Spanish Ingenio satellite, an optical satellite with 2.5m resolution built by Airbus.
• Tentative launch of the Spanish Paz satellite, a SAR satellite with 1m resolution also built by Airbus.
• Planned launch of the Italian OpSat satellite, an optical satellite with a resolution under 1m built by Israel Aircraft Industry. It is a compensation for the sale of Italian trainer jets to Israel.



• Planned launch of the first CSO satellite.
• Planned launch of the first German SARah satellite, the follow-on system to SAR-Lupe. It will be joined by two passive SAR satellite flying in formation with it.
• Planned launch of the first of two Italian Cosmo-Skymed 2nd Generation (CSG) satellites.


Planned launch of the first Falcon Eye satellite, a Pleiades-derived system built jointly built Airbus and TAS for the United Arab Emirates. The sale put the French industry in competition with US manufacturer Lockheed Martin. Politics played an important role in the contract, as US shutter control was cited as a reason for the French win. ITAR issues almost killed the French offer, and had to be resolved at presidential level between France and the US. Resolution is probably around 35cm.


The CERES constellation

• Planned launch of CERES, a constellation of 3 formation-flying satellites with radio and radar emitter detection, identification and location capabilities. Contrary to its predecessor electronic intelligence satellites, it will be the first designed for operational use by the armed forces.
• Planned launch of the first of 4 next-gen, high-resolution commercial satellites operated by Airbus. They will probably have a resolution around 30cm.


• Planned launch of the last CSO satellite.
• Planned launch of the last of the 4 Airbus next-gen commercial satellite.
• By that date, the French Minstry of Defence plans to acquire 650 satellite images per day, which creates concerns about image analyst workloads.



The use of space in French operations

Space, luxury or necessity: situations and prospects for France after the Livre Blanc and Opération ServalGuilhem Penent. 2013

Space for Operations. Les cahiers de la Revue Défense nationale. 2011

Hearing of the French Space Command Chief by the National Assembly (in French). 2016

Hearing of the Director of Military Intelligence by the French National Assembly (in French). 2015

Report of the French National Assembly on imagery intelligence (in French). 2001

L’espace au profit des opérations militaires. French MoD website.

Espace et opérations: Enseignements et perspectives. General Pascal Valentin. 2012.

La Vérité sur notre Guerre en Libye. Jean-Christophe Notin. 2012.

Early history of the reconnaissance program (up to SAMRO)

The Interest and Opposition of the French Military in Satellite Reconnaissance for France: A Talk with a General Officer of the French Forces   Sébastien Matte La Faveur. 2006

Histoire politique des services secrets français: De la Seconde Guerre mondiale à nos jours. Roger Faligot, Jean Guisnel, Rémi Kauffer. 2013

Au service secret de la France: Les maîtres de l’espionnage se livrent enfin…  Jean Guisnel, David Korn-Brzoza. 2014


Technical overview of Spot 1 to 5

Eoportal page on Spot 4

Eoportal page on Spot 5

Eoportal page on Spot 6 and 7

History of CNES in the 1970s (in French)


Spacenews article on Helios 2

Official CNES page

Helios 2 brochure


Eoportal page

Official CNES page


Official CNES page

Falcon Eye

Comment la France a vendu deux satellites d’observation hyper sophistiqués aux Emirats Arabes Unis. Michel Cabirol, La Tribune, 23 June 2013


Thanks to MarsSurfaceWanderer from forum-conquete-spatiale.fr for pointing out mistakes, and to Starking for providing information on the 1960s-1970s period.

Thanks to Blackstar from nasaspaceflight.com for providing the article from Sébastien Matte la Faveur on The Interest and Opposition of the French Military in Satellite Reconnaissance for France.

Persistent Surveillance

The future of Earth observation, Part III

This post is a part of a series on the future of earth observation, and is a follow up to  The Future of Optical Earth Observation I: The road so far  and The Future of Earth Observation II: What do users really want, anyway?

Originally, satellite imagery consisted of just that: images. However, there is limited information in a static snapshot of a scene. The sense of depth, in particular, is lacking. This can be compensated by taking two images of the same scene from different points of views, to get a 3D representation the same way our two eyes are used two build a 3D representation of the world.

But why stop at only two images? Our eyes do not, and continuously capture images, enabling us to see the motion of objects, and extract meaningful information out of this motion. Satellites can do the same, by acquiring images in quick succession:

These videos were captured by the SkySat satellite from Terra Bella (formerly Skybox), and show the kind of information that video from space can add to static imagery. They have a high framerate: the time between consecutive images is short enough that our eyes see continuous movement. This time can be increased, making the movement choppy but still exploitable, like in this  pléiades timelapse.

LEO limitations

Unfortunately, this kind of video cannot last very long: due to the movement of low earth orbit (LEO) satellites, they move in and out of sight of a given location in a few minutes. This movement can be seen in the changing parallax of the pléiades video: the angle of the building changes as the satellite passes over them. Thus, the persistency (the duration of available video) offered by the low-orbit satellites is limited.

Movement of a low orbit satellite over time: ticks are 1 minute apart

Moreover, the video is not available on-demand: the satellite has to pass over the location to be imaged, and due to orbital mechanics, this can take hours or days. To get a second video later, the satellite has to revisit the place, which also takes hours to days. So revisit, the time between two possible video acquisitions, is very important. Typically a constellation of two agile LEO satellites on a 700km orbit can provide daily revisit for places at the equator

User needs

So standard LEO satellites have serious persistency and revisit limitations, which is an issue since some users would like to be able to watch any place continuously, 24/7, in a drone-like fashion. For instance, for crisis management (see The Future of Earth Observation II), a short revisit is needed. The applications enabled by different levels of persistency and revisit are summarized in the graph below:

Revisit and persistency requirements for several applications (from IAC-13, B1, 2, 4, x18937 EADS  New Generation of Earth Observation Optical Systems )

Mobile object tracking and tactical operations monitoring are especially interesting for military users: Since knowing is half the battle, having the precise position of enemy ships and planes is a significant advantage. For ground operations, constant monitoring has proven its value through the widespread use of drones in recent American wars and occupations. Several projects on the use of drones for wide-area persistent surveillance are in active development or in use. However, drones cannot be everywhere nor be deployed instantly, and using them in a foreign airspace can cause diplomatic problems, whereas a satellite solution does not violate any borders and ideally could watch everywhere all the time. The strategic intelligence gains provided by constant monitoring are also significant: it ensures that no interesting activity is missed.

Since military and intelligence applications are promising and the corresponding budgets can be generous, a potential market for high-persistency, high-revisit satellite imaging exists provided the cost of such a system can be kept reasonably low. The problem is there is a hard tradeoff to be made between the number of satellites of the system and their complexity: doing it with LEO satellites requires a lot of relatively simple satellites, because each satellite offer poor revisit and persistency on its own. Doing it with satellites on higher orbits requires fewer, but much more complex satellites. This is because there is a direct relationship between the altitude of a satellite and the persistency it provides: the higher the orbit, the longer the persistency.

Persistency vs orbit altitude (orange curve). For orbits lower than 10 000km, the relationship is almost linear (from IAC-13, B1, 2, 4, x18937

Technical solutions

There are three ways to solve this tradeoff: a constellation of tens of LEO satellites, which will be treated in a later post, a few satellites in Medium Earth Orbit (MEO), or one to three satellites in Geostationary orbit (GEO)

MEO constellation

Proposed elliptical orbit for a High Temporal Revisit (HRT) satellite (from IAC-13, B1, 2, 4, x18937)

Since persistency is limited by the orbital altitude, the first thing to do to expand it is to increase the altitude. This can be done using elliptical orbits with apogees up to 6000km, as shown in the picture above. Because the orbit is elliptical, the satellite has a lower speed at apogee, and thus hangs around it for a longer period of time compared to a circular orbit.

Increasing the orbit raises three issues: first, the size of the satellite’s telescope, specifically the diameter of its primary mirror, has to be increased proportionally to altitude in order to keep the same resolution. For a 6000km orbits, this is roughly a 10x increase compared to a LEO satellite. This increase in size translates in an even bigger quadratic increase in mirror mass: mirror mass depends on the area of the mirror, so a 10x increase in diameter results in a 100x increase in mirror mass if the same technology is used. The mass of the mirror is such an important point for high-resolution optical satellites that there is a constant research effort on the use of lightweight materials and lightweight structures for mirrors.

The second problem with MEO orbits is radiation: Earth’s magnetic field traps radiation, and at 6000km this radiation is much more intense than in LEO. Finally, the third issue with high elliptical orbits is that they require more energy to be reached than LEO. This limits the mass a rocket can inject in such an orbit.

Interestingly, there has been at least one MEO satellite program that has reached orbit: the Russian Araks program. A first satellite was launched in 1997 and failed quickly after reaching orbit, a second in 2002 failed after one year. The third was not even launched. The satellites sported a 1.5m mirror, probably able to produce 1.3m imagery from the satellite’s 2800km x 1500km orbit. Araks was supposed to be complemented by the Sapfir project, on a 10 000- 20 000km orbit.

The USA is speculated to have thought about  MEO satellites then dropped the idea.  The leaked 2013 intelligence budget documents do not mention any high-orbit electro-optical satellites.

In France, Thales Alenia Space and Airbus have studied the question. Airbus in particular did architecture studies on a HRT (High Temporal Resolution) project, consisting of one or two satellites on an elliptical orbit with a 6500km apogee. This would grant 30 to 45 minutes of persistency per satellite, and a revisit of 3h with one and 1h30 with two.  With four satellites, the system would be able to provide continuous coverage during roughly 6 hours each day. The satellites would use 3m mirrors, giving a resolution of 1.5m. A 5m mirror,  as large as the largest fairings of commercial rockets, would provide a resolution just under 1m.

Overall, Medium Earth Orbit systems are interesting because they offer significant persistency for a moderate technical risk. They can provide exploitable resolution using reasonably large mirrors that can be launched in one piece, without any complicated deployment mechanism. Such 2 to 3m mirrors are already manufactured or planned to be manufactured by the USA, Russia and China, so no optics breakthrough are needed for them, and they could decide to launch such systems relatively quickly.

Geostationary orbit

Since the persistency offered by MEO orbits is high but still not round-the-clock,  there is only one solution to get full persistency: putting the satellites in geostationary orbit (GEO), 36 000km away from Earth. From the ground, objects in this orbit appear to be fixed in the sky because they follow the rotation of the Earth. Thus, a GEO satellite can stay pointed a given location 24 hours a day, every day of the year. This feature is used by communication satellites to provide uninterrupted communications. It can also be used by imaging satellites: for instance, GEO weather satellites provide images of the whole Earth disk every 30 minutes or less, in order to be able to see cloud movement.

Weather satellites typically have spatial resolution in the hundreds of meters, far too low to be useful for surveillance. But a GEO satellite with a big enough telescope could provide truly persistent surveillance with high enough resolution. The question is, how big of a telescope is needed? As can be seen in the graph below, the answer is “really big”:

Mirror diameter vs ground resolution from GEO

The graph reads as follows: a 1m diameter telescope provides a 20m ground resolution. It can also be read the other way around: a 20m telescope provides 1m resolution. So extremely large telescopes are needed to reach high resolution. For comparison, the largest ground telescope currently only has a diameter of 10.4m, and ground telescopes will not reach 20m before the early 2020s.  The largest mirror ever launched in space is to public knowledge the Herschel space telescope, with a diameter of 3.5m. The James Webb space telescope will only reach 6.5m, after years and billions of dollars of development.

Consequently, because GEO is much further than MEO, much bigger mirrors are required for the same job, and the technology is not there yet to build metric-resolution systems. However, lower resolution systems can already be useful: for instance, China has launched the Gaofen-4 satellite. From GEO, its provides 50m resolution visible light images, and 400m resolution infrared images. This is enough to detect large ships, as can be seen in the images below, and probably to classify them by type, thanks to the persistency of the imagery:


50m resolution only requires a 0.4m mirror, which is very reasonable and can fit on a standard geostationary platform. India is also building a 50m-resolution GEO satellite called GISAT-1, scheduled to launch in 2017. GISAT-1 will even have hyperspectral capabilities, to be better able to identify the content of each pixel in spite of the low resolution.


In the USA, the DSP missile early-warning satellites located GEO since 1970 eventually became able to detect large aircrafts on afterburner, and passed this information to the Navy in near real-time. These satellites use low-resolution thermal infrared sensors, with very low resolution (probably around 1km).  However, even with this low resolution, they can provide interesting real-time intelligence: for instance they can also detect aircraft crashes, and the afterbuner use mentioned above. The follow-on SBIRS program improves on these capabilities (denominated SLOW WALKER) and might even detect tactical missiles and artillery explosions.

European industry has also been working on the subject. ESA and Airbus have a design called GEO-oculus, able to provide 13m resolution thanks to a 1.5m mirror. Airbus also has a design called GO-3S (for Geostationary Observation Space Surveillance System), with a 4m mirror. Airbus advertises a 100km x 100km field of view, with a 5 frames per second refresh rate and 3m resolution, although by traditional measures the resolution would be around 5m. The high frame rate combined with the moderate resolution enables the detection of moving objects such as cars, with a high probability of detection, even if they are smaller than the ground resolution:


Additional GO-3S videos can be found there and there. Due to current launcher mass and fairings constraints,  4m to 5m mirrors is the largest size that can be launched to GEO while keeping a traditional mirror made of a single piece of glass, which makes the satellite relatively simple and affordable. Bigger mirrors require breakthrough beyond the current sate of the art.


The path to large optics

One way overcome the limits of fairing size is to split up the main mirror into several smaller mirrors and fold them inside the rocket fairing so that it fits. After launch, the system unfolds, the mirrors are then aligned with sub-micron precision, and function together in the same way as a single-piece telescope of roughly the same size. This is the solution used in the James Webb Space Telescope (JWST) to reach the required 6.5m mirror size while still fitting inside a 5m-diameter Ariane 5 fairing.

The James Webb Space telescope, in deployed and folded forms. (Credit Emigepa)

This segmented-optics solution is extremely expensive: the JWST is scheduled to cost 8 billion US dollars and has been in development for more than ten years. However, it does not operate on visible light: a visible-light equivalent of the JWST  requires an even finer alignment of the mirrors, pushing the technology even more. But is not impossible: the NRO has developed a 3m segmented telescope prototype, the Segmented Mirror Telescope, and made its existence public in 2010.


The Segmented Mirror Space Telescope

To reach larger diameters, more exotic configuration are required, such as this multiple-mirror concept by Thales, presented at the 2010 ESA High Resolution GEO imaging workshop:


However, the complexity and the remaining mass and packaging constraints of deployable mirrors make them a highly risky solution for large mirrors in the 10-20m range. So other technologies have to be explored. Enter MOIRE, a DARPA program contracted to Ball Aerospace, to study a game-changing optical solution. MOIRE stands for Membrane Optical Imager (for) Real-time Exploitation, and studied the use of a thin membrane to form images. This technology promises a 7x reduction in mass and 10x in cost compared to rigid mirrors, and makes diameters of 10m to 20m realistically achievable. Ball successively demonstrated ground operation of a small-scale model. China is also working on this technology, with similar objectives.

MOIRE demonstrator schematics


Comparison between MOIRE and current large telescopes


Finally, a solution might come with the introduction of new rockets with larger fairings in the coming years, if they do reach the launchpad: SLS block 2 will have a 10m fairing, the New Glenn rocket from Blue Origin a 7m one, and the SpaceX Interplanetary transport system is designed with a 12m diameter. Large fairings can be combined with other solutions: NASA is studying a 12m-diameter segmented mirror telescope launched by the SLS block II as a potential Hubble successor.

Size comparison of current and planned launchers



Overall, the geostationary orbit provides an interesting persistent surveillance capability, but only at moderate resolution in the near term. For higher resolutions, medium Earth orbit offers a good mix of persistency and image quality, while low Earth orbit promises high revisit rates with simple satellites, as we will see in the next post of this series.

The Chinese maritime surveillance system

An analysis of the Chinese reconnaissance satellites, and their maritime surveillance capabilities

This article initially appeared on eastpendulum.com, a French-language blog about the Chinese military and aerospace industry


Historical context


Ever since the Communist Party conquered mainland China in 1949, the island of Taiwan has been a source of tension in the region. The defeated Republic of China (RoC) government fled to this province, and has survived mostly thanks to the 100-mile Taiwan strait that separates it from the People’s Republic of China (PRC), and thanks to the military support of the United States. The last major crisis between the two Chinas took place in 1996: after the Taiwanese president visited the USA, the PRC organized large and intimidating military exercises. Eventually, the USA sent two carrier battle groups in the region, forcing the PRC to stand down. In reaction, the PRC launched several new weapons program, in order to deter the Americans from intervening again.

One of the main objectives of these programs is to be able to credibly threaten a US aircraft carrier. In addition to being extremely well defended, the carriers and their attached battle groups are also very mobile. Locating them is a difficult task, as a ship going 20 knots can cross 500 nautical miles (800km) a day. The first step of a carrier hunt is consequently a high-stakes game of hide and seek.

One of the ways the Chinese tried to solve this problem was to develop a space-based maritime surveillance system, with electronic intelligence, radar and optical satellite constellations. The aim of this article is to give a survey of these constellations, and to assess how much their combined capabilities give China an accurate and comprehensive picture of the situation at sea.


I. The electronic intelligence system


JianBing 8 constellation

Satellites: Yaogan 9, 16, 17, 20, 25

Type: ELINT (+ optical & SAR?)

Orbit: 1100x1100km, 63°


Yaogan 9 ? (CAST)
Yaogan 9 ? (CAST)


This constellation is made up of 3 orbital planes, all inclined 63°. Each plane contains one or two triplets of satellites flying in close formation. Theses characteristics are very much like those of the US NOSS/INTRUDER constellation, which is dedicated to detecting, identifying and locating radars and telecommunication emitters, including those carried by warships. The JB-8 constellation most likely fills the same role.

Consequently, the satellites can only detect ships which are not under radio silence, as is often the case during crisis situations. Ships can also avoid detection by turning off their radar when the satellites are overhead (roughly 20 minutes every hour and a half). However, these satellites might also detect the radars carried by carrier-launched early warning planes, giving a rough location for the carrier itself.

Some sources mention that each triplet also carries optical and radar sensor. If it is the case, these sensors probably provide limited coverage: the 3 satellites of a triplet fly close, so the sensors they carry have the same viewing angle constraints. Besides, it would seem more logical to take the  time to analyze the data from this system, and then task other satellites later, to get more data on interesting detections.

5 triplets have been launched, with the last 3 probably replacing the first two, which are getting old:

Satellite Local time of passage Launch year Comments
YG 9 a/b/c Variable, as the orbit is not sun-synchronous 2010
YG 16 a/b/c same 2012
YG 17 a/b/c same 2013
YG 20 a/b/c same 2014 Probably replaces YG 9
YG 25 a/b/c same 2014 Probably replaces YG 16



Les 3 plans orbitaux de JB-8
The three JB-8 orbital planes


Trace au sol d'un vieux triplet et de son remplaçant
Ground track of an old triplet and its replacement


Trace au sol des 3 triplets récents
Ground track of the latest 3 triplets


II. The radar system


JianBing 7 constellation

Satellites: Yaogan 6, 13, 18, 23

Type: SAR

Orbit: polar sun-synchronous, 520x520km


Yaogan 13
Yaogan 13


Synthetic Aperture Radar (SAR) satellites are very useful in maritime surveillance, thanks to their wide swath, which can reach several hundred kilometers. This enables them to find ships, given a very rough idea of where they might be, in any weather. However, the wide swaths modes of such a system generally have a low resolution, measured in the tens of meters. This makes ship identification difficult. Consequently, a higher-resolution system, or another pass of the same satellite but in high-resolution mode, are needed. Ship motion can severely limit the image quality in high-resolution modes.

For ground observation, the high-resolution modes are often used, as the location to be imaged is generally known in advance.


Images SAR haute-résolution. On voit que l'identification des navire nécessite de l'entrainement
High-resolution SAR images. It is clear some training is required to identify objects.


Unlike classical optical satellites, radar systems can be used at night, and consequently can provide images more often.

The constellation is made up of the following satellites:

Satellite Local time of passage Launch year Comments
YG 6 9:40 2009
YG 13 12:40 2011
YG 18 10:00 2013 Probably replaces YG 6
YG 23 13:20 2014 Probably replaces YG 13


Orbites de la constellation JB-7
Orbits of the JB-7 constellation


The satellites fly in pairs, with one pair providing morning passes and the other afternoon passes. Each pair is made up of one relatively recent and an older satellite, which may be out of service. If all four satellites were active, it would provide each day one morning revisit, one during the afternoon, and two at night, with a maximum viewing angle around 45°. Since the orbits are sun-synchronous, the same satellite always passes over a given point in the ground at the same local time. The times indicated in the table above are for places located at the equator; for other places the time is shifted by a few minutes.

According to the image above, YG-13 looks like Gaofen-3, a Chinese civilian satellite which was launched in 2016. To give an idea of the performance of Chinese SAR technology, Gaofen-3 has a maximum resolution of 1m and a maximum swath width of 650km, from a 730x730km orbit. Even a pair of such satellites would not be sufficient to cover all the oceans’ surface every day, but would be enough to find all ships in a relatively wide region of interest.


Gaofen 3
Gaofen 3


JianBing 5 constellation

Satellites: Yaogan 1, 3, 10, 29

Type: SAR

Orbit: Dawn-dusk polar sun-synchronous, 620x620km

Yaogan 1
Yaogan 1


This constellation is also a SAR constellation, but its satellites fly higher and pass during dawn and dusk. That way, their solar panels are always lit and they have more electrical power.

The constellation is probably made up of only two active satellites:

Satellite Local time of passage Launch year Comments
YG 1 6:00 2006
YG 3 5:20 2007
YG 10 5:20 2010 Probably replaces YG 1 or 3
YG 29 4:40 2015 Probably replaces YG 1 or 3, with a newer design


Orbites de la constellation JB-5
Orbits of the JB-5 constellation


With two active satellites, this constellation would provide a morning revisit and an evening revisit every day, with a maximum viewing angle around 45°.


III. The optical system


JianBing 6 constellation

Satellites: Yaogan 2, 4, 7, 11, 24, 30

Type: Optical

Orbit: Polar sun-synchronous, 630x630km


Yaogan 11 (CCTV)
Yaogan 11 (CCTV)


This optical constellation is probably made up of two or three active satellites. They are positioned on a classical orbit for such a system, and provide morning and afternoon revisits.

If the images shown by the Chinese state television are to be trusted, these satellites carry two cameras, probably to widen their swath. This solution is also used on the civilian Chinese satellites Gaofen 1 (2m resolution, 69km swath) and 2 (0.8m resolution, 45km swath). It is typical of Chinese satellites, as their 1m resolution or better foreign counterparts usually carry only one telescope. A dual camera system can also be used to acquire stereoscopic images, in order to build terrain elevation models. In that case the swath is the same as a single-camera system.

These satellites do not seem to have a wide enough swath to be useful for maritime surveillance anyway: a 70km swath is very small compared to the area of that has to be covered to detect ships in the open ocean. Even to identify ships which have already been located, such a swath width means a ships going 30 knots can get out of the field of view in around 40 minutes. Consequently these satellites can only be used to image ships if they have been located very recently.

Satellite Local time of passage Launch year Comments
YG 2 12:40 2007
YG 4 6:00 2008 Pass time is too early for an optical satellite, so probably out of service
YG 7 15:40 2009
YG 11 9:00 2010
YG 24 13:00 2014 Probably replaces YG 2, with a newer design
YG 30 9:00 2016 Probably replaces YG 11, with a newer design


Orbites de la constellation JB-6
Orbits of the JB-6 constellation


JianBing 10 constellation

Satellites: Yaogan 5, 12, 21

Type: Optical

Orbit: Polar sun-synchronous, 500x500km

Yaogan 5
Yaogan 5

This second optical constellation is placed on a lower orbit, and provides only morning passes. Thus, it probably has a higher resolution than JB-6. On the image above, a dual-camera system can be seen, along with a data-relay antenna (the red dish pointing upwards). The relay system uses the 3 geostationary Tianlian satellites, and is probably used by all Chinese reconnaissance satellites.

These satellites probably have the same limitations for maritime surveillance as the JB-6 ones.

Satellite Local time of passage Launch year Comments
YG 5 Deorbited 2008
YG 12 10:00 2011
YG 21 10:30 2014


Orbites de JB-10
Orbits of the JB-10 constellation


JianBing 11 (?) constellation

Satellites: Yaogan 14, 28

Type: optical

Orbit: Polar sun-synchronous, 500x500km

Yaogan 14
Yaogan 14

This constellation seems to be the afternoon equivalent of JB-10. The JB-11 designation is speculative.

Satellite Local time of passage Launch year Comments
YG 14 14:00 2012
YG 28 14:00 2015


JianBing 12 (?) constellation

Satellites: Yaogan 26

Type: Optical

Orbit: Polar sun-synchronous, 500x500km

Yaogan 26
Yaogan 26 (Gunter’s Space Page)

This satellite is placed on the same orbit as the JB-10 constellation, but could be of a different model. According to the picture above, it carries a single large-diameter telescope. The Changchun Institute of Optics is known to work on such 1.3 to 1.6m telescopes, which provide a 20 to 25cm ground sampling distance if carried by Yaogan 26. Such a high resolution would be traded against swath width, making the satellite less useful for maritime surveillance. The JB-12 designation is also speculative.


Satellite Local time of passage Launch year Comments
YG 26 11:00 2014


JianBing 9 constellation

Satellites: Yaogan 8, 15, 19, 22, 27

Type: Optical

Orbit: Polar sun-synchronous, 1200x1200km



This constellation is placed on a surprisingly high orbit for optical satellites. Because of this height, the spatial resolution is lowered but the swath is increased. The constellation is made up of a first pair of satellites, which provides morning passes, and a second pair for afternoon passes. This enables same-day revisit of any point a the globe, with a small viewing angle (around 25°). It also makes extremely short revisit times possible: the two satellites of a pair follow each other, with a separation of 10 minutes. Thus, they can successively observe the same region with an acceptable maximum viewing angle (around 45°) and estimate the speed of ships in this region.

According to a biography of Chinese scientist Ren Jianyue, this constellation is dedicated to maritime surveillance, and combines a wide swath and a high resolution. The satellites carry an off-axis Cook-TMA telescope, made out of silicon carbide, and are able to identify ships thanks to a wide swath (between 100 and 1000km) and a high resolution( <10m). According to the NIIRS scale, ship identification requires at least a 4.5m resolution. Other sources indicate precise classification requires 0.8m. JB-9 probably has a performance between those two figures.


Le télescope Cook-TMA de EO-1
The Cook-TMA telescope aboard EO-1


The Cook-TMA telescope design has been used by NASA for the EO-1 satellite: it offers a 15° field of view, which translates into a 185km swath from a 700km altitude. This would be coherent with the JB-9 pictures above: a field of view around 20° would explain the angled baffles. Such an instrument would give the JB-9 satellites a swath width around 320km, which is comparable to a SAR satellite, but with a much better resolution.

The swath could possibly be even wider if the satellites are agile enough to be repointed quickly. For instance, very agile satellites such as Spot 6 can be repointed to image a square region 6 times wider than their swath, in a single pass. JB-9 agility is probably lower, as evidenced by their large solar panels, but it’s not impossible they could double their swath by repointing.

Satellite Local time of passage Launch year Comments
YG 8 7:40 2009 Time of passage is early for an optical satellite, so may be out of service
YG 27 09:40 2015
YG 19 10:20 2013
YG 22 13:00 2014
YG 15 14:00 2012


Le vol par paire des JB-9
The two JB-9 pairs


Trace au sol des JB-9
Ground track of a single pair


These satellites might also carry a thermal infrared sensor, enabling them to detect and maybe identify ships at night.  Another possibility is that they also have a low resolution but ultra-wide swath camera, like the one used by the Gaofen-1 civilian satellite. Such a camera would have a swath of 1550 km and a resolution of 30m from a 1200km altitude, enough to cover all the oceans with two satellites and detect large ships such a oil tankers and aircraft carriers.


La caméra champ large de Gaofen-1
The  Gaofen-1 wide field cameras


Trace au sol de la caméra champ large de GF-1, en vert. A 1200km d'altitude elle serait 2 fois plus large.
Swath of the wide field GF-1 camera, in green. At 1200km altitude, the swath would be twice as wide.


According to public pictures, the civilian Gaofen-8 satellite looks like a JB-9 satellite, but it flies much lower, at an altitude of 500km.


Gaofen 4

Type: Optical

Orbit: Geostationary, 105°E


Gaofen 4 is a one-of-its-kind satellite: launched in 2015, it is the only high-resolution imaging satellite to be placed in geostationary orbit. With its 50m resolution, it provides images 10 times sharper than the weather satellites on the same orbit. Since it is stationary in the sky, and is always placed 36 000 km above Singapore, it can revisit a place extremely frequently, and it can even produce video sequences, to make change detection easier. It has a 400km field of view, and it can image any region in the East Asia at any time. It also has an infrared sensor with 400m resolution, to take pictures at night.

These features enable the satellite to detect and track large ships, and probably to determine their type based on their speed, their heading and their thermal signature. Detecting smaller ships light also be possible.


IV. Assessment of the overall system


Maritime surveillance can be split into two separate tasks:

  1. Detecting and identifying all ship in a wide area
  2. Tracking specific ships over time, once they have been identified

In order to assess the capabilities of the Chinese maritime surveillance system, let’s take conservative hypotheses:

  • During a crisis, warships are under strict emission control, which makes the electronic intelligence system blind.
  • Each SAR constellation has only two active satellites.
  • SAR satellites have a 300km swath, and not enough resolution to identify ships.
  • Apart from the JB-9 constellation, the low Earth orbit optical satellites do not have a large enough swath to be useful for maritime surveillance.
  • The JB-9 constellation has 4 active satellites, with a 300km swath and no infrared capability.
  • The satellites can only image 10 minutes per orbit, which means the maximum swath length is 4000km.
  • The geostationary Gaofen-4 satellite cannot detect ships smaller than an aircraft carrier.

With these hypotheses, there are 12 satellite passes a day for a given location:

Heure locale des passe de satellites au cours de la journée
Local time of satellite passes


Detection and identification

The performance of the constellation regarding the detection of all ships in a large area depends on the combined swath of all its satellites, compared to the distance between two satellite passes. For instance, if the constellation had only one satellite with a 3000km swath, and if the distance between two successive passes at the equator were also 3000km (which is typical for a low Earth orbit satellite), then it would be able to cover all of Earth’s surface each day.

With the hypotheses above, the combined swath is 300km x 12 = 3600km. The system can consequently provide full coverage over a 3000km x 4000km area, each day, and detect all ships in this area. However, since only the JB-9 constellation can identify ships, identification can be performed in third of the area.


Coverage of the constellation in East Asia over 24h . China and Taiwan are in the top left corner.(Red squares: JB-9 coverage Green: JB-7 Blue: JB-5). Click for animated GIF. In the simulation, satellite pointing has not been optimized for maximum coverage, so it is possible to have less overlap and more coverage.



In order to optimally track a ship which has been identified beforehand, the satellite passes have to be spread out at regular intervals during the day. This is not the case: two successive passes can be up to 4h40 apart (for YG 10 and YG 18 in the evening). This is enough for a ship going at 30 knots to cross 250km, which can result in it getting out of the field of view of the tracking satellite.

Besides, as SAR satellites fly relatively low, only half of them have a low enough viewing angle to image a given location on a given day, so only four SAR passes each day can be used to track a specific ship. Consequently, a ship which changes course regularly has a good chance of making the constellation lose its track from time to time. This would force the constellation to go back to search mode to reacquire the track.

However, around 10:00 and 13:30 local time, the pass of a pair of JB-9 satellites can provide the location, heading and speed of a ship, and confirm it identification. This is enough to establish a solid track, which could be used as a firing solution for the Chinese Anti-Ship Ballistic Missiles, or for more conventional missiles fired by planes or ships close to the target.




Thanks to its satellites, China has optical, radar and electronic capabilities to detect, identify and track ships at sea. Even without taking into account real-time tracking from geostationary orbit, the wide-angle JB-9 constellation and the JB-5 and JB-7 SAR constellations can find contacts in a vast area every day, and have a good chance of refreshing the location of the most interesting ships every few hours. Consequently, it seems unlikely a naval group could hide in the ocean for long.

However, when the weather is very cloudy, only the SAR satellites are able to look through, which severely limits the capabilities of the system. This does not mean China is blind: other means of detection, such as it trans-horizon radars, or its long range patrol aircrafts can complement the satellite system, and help challenge the defenses of US aircraft carriers. This makes a US intervention in a new Taiwan Strait crisis much more risky, and consequently less likely.




In Chinese:

Article on maritime reconnaissance in the Jianchuanzhishi journal

Biography of Chinese academic Ren Jianyue

Overview of the activities of the Changchun Institute of Optics

Gaofen-4’s ship tracking capabilities

In English:

Eoportal Page on the EO-1 satellite

Eoportal Page on the Gaofen-1 satellite

Eoportal page on the Gaofen-2 satellite

List of Chinese military satellites on Gunter’s space page

The Airbus Very High Resolution constellation

Airbus Defense & Space just announced it will launch a constellation of 4 Very High Resolution (VHR) optical earth observation satellites, in 2020 and 2021. This will be a follow-on to the Pléiades constellation, which comprises two agile, 70cm resolution satellites, launched in 2011 and 2012. Unlike Pléiades, which was a public-private partnership between Airbus (the prime contractor), Thales (which provided the instruments) and the French Ministry of Defense, this new constellation will be entirely financed by Airbus.

Pléiades (Airbus Defense & Space, France)

According to the press release, “Pléiades system features will be improved to match the market requirements expected to be the norm at the time of launch”, which I think means the resolution will be improved to 30cm, to match the resolution of the Worldview 3 and Worldview 4 satellites owned by Airbus’  main competitor, Digital Globe. This would be coherent with the studies on the design of 20 to 30 cm resolution satellites carried out by CNES, the French space agency.

These studies led to the ARCTOS concept by Airbus, with a 30cm resolution from 700km up, a 20km swath, and a small enough mass to be launched from a Vega launcher thanks to a lightweight 1.5m SiC mirror. Resolutions higher than 30cm are much more difficult to achieve. Besides, the release calls the constellation “VHR”, which is between HR (around 70cm, like Pléiades) and EHR (extremely high resolution, around 20cm) in the French classification of resolution. Airbus is also the prime contractor for CSO,  a military EHR satellite to be launched around 2020, but this satellite fly will relatively low in order to achieve this resolution, so the technology is probably not mature for an EHR satellite at 700km altitude. CNES, Airbus and Thales are also working together on the OTOS concept, which would use adaptative optics to correct for mirror deformations.

Consequently, it is likely the announced constellation will be made of four 30cm resolution satellites. Since the release states it will provide “intra-day” revisit, this means the constellation will have two orbital planes: from a 700km orbit, two agile satellites on the same orbital plane are required to provide same-day revisit, so two planes are needed.

This constellation will help Airbus catch up with Digital Globe, but the US company has already announced it is designing its next-generation constellation, which will be made up of six 1m-resolution satellites build and operated by the United Arab Emirates and a high-resolution component owned by Digital Globe. The emirati satellites will provide a high temporal revisit, enabling to detect changes  and then cue the higher resolution satellites to characterize these changes. The former are scheduled for launch in 2018 and 2019,  around the same time Digital Globe plans to seriously invest in the latter.

Finally, the release mentions the constellation will be “dual”, which probably means it will be a dual-use civilian and military constellation, giving the French Ministry of Defense  tasking priority when required. This would considerably increase the temporal revisit capability of the French reconnaissance system.

Edit: Spacenews quotes an industry official saying Airbus will invest at least 550m€ in the constellation, the resolution being not set but around 40cm, and the instruments being Airbus-made SiC telescopes.

Update 26 January 2017: Peter B. de Selding reports the satellites will use the EDRS network for laser data relay, enabling near-real time access to the images.

Update 12 May 2017: Airbus will probably use CILAS deformable mirrors for its satellites, as CILAS and Airbus are collaborating on the OTOS program and the technology seems mature.

History of the US reconnaissance system

I wanted to make a short post on today’s US spy satellites, but I realized that to speculate about them, it’s better to have some historical perspective. So I assembled a condensed history of the US reconnaissance system (only for imagery, the electronic side might come later). I used Susan D. Schultz’s chronology in Why Gambit and Hexagon? U.S. National Security and the Geopolitical Setting, 1957–1960 as a starting point, and expanded it with more technical information on the reconnaissance systems, and with relevant events up to the present day.  I removed quite a bit of it, so if you want more detail on the geopolitical setting of the 50s, 60s and 70s I encourage you to read at least the chronology in the link.

So here is a timeline of the US strategic reconnaissance system, from 1947 to today:

The RAND Corporation delivers to the Air Force a report concluding that artificial satellites are feasible in the near term.

The Central Intelligence Agency (CIA) is created.

Stalin blockades all ground access to West Berlin. The US respond by airlifting supplies to the city.

• The People’s Republic of China is founded.
• The USSR successfully tests its first atomic bomb.
• The US uses peripheral flights to monitor the borders and coasts of the Warsaw Pact, but is almost blind to what happens deep inside its territory.

A B-36 bomber, used for USSR overflights.

Beginning of the Korean War.

End of the Korean War, Korea is split in two.

After several preliminary studies, the RAND corporation delivers a feasibility study on a reconnaissance satellite that would carry a television camera in orbit and radio its images back to the ground. The Air Force uses that report to start a reconnaissance satellite project, the WS-117L program.

• The Soviets reject President Eisenhower’s  ‘Open Skies’ proposal, which would have allowed the two superpowers to monitor each other using specific  reconnaissance flights.
• The Soviets display a flight of their new Bison bomber at an air show, to the surprise of the USA. US intelligence mistakenly concludes the bomber is in mass production and warns of a bomber gap. The Air Force successfully argues for expanding its bomber program in return.

• First launch of air balloons carrying cameras over the USSR. The project ends in February due to Soviet protests.
• First reconnaissance flights of the U-2 Dragon Lady spy plane over the USSR.
• The USSR invades Hungary.

The glider-like U-2

• U-2 overflights of Soviet bomber bases demonstrate the Soviet bomber fleet is much smaller than previously thought, putting an end the idea of a bomber gap.
• The USSR launches into orbit Sputnik, the first artificial satellite. This shocks the American public opinion, as it demonstrates the USSR is ahead of the USA in rocket technology. As rockets can be used to deliver nuclear bombs, it creates in the US the fear of a missile gap: the USSR could have a large number of ballistic missiles (ICBM) soon, and use it to wipe out the USA in a surprise attack.
• Consequently, the USA needs to gather intelligence on the Soviet rocket program. Since the efforts up to that date have only produced vague, unreliable intelligence, a very high priority is given to the satellite reconnaissance program. The WS-117L program is reorganized. It is split into 3 components: the high-priority television reconnaissance program, a lower-priority film-return reconnaissance program and a missile-warning program. The film return component, which is the most promising in the short term, is put under CIA management. The plan is to use it as stopgap measure until the television system in ready.
• The US ICBM program is also given a boost, to try to balance the Soviet perceived advantage.

Explorer I, the first US satellite, reaches orbit.

• First successful image return from a film satellite: after many failed attempts, the film capsule of a KH-1 Corona is successfully retrieved. Corona satellites carry a camera that captures images on film, which is then placed in a reentry capsule. The capsule is separated from the satellite, reenters the atmosphere, and is recovered mid-air by Air Force planes. The satellite reenters separately and is destroyed in the process. The first Coronas have a medium resolution, in the order of 8m (25 feet). However, the first successful flight brings back more imagery than all the U-2 flights combined. As a result, the Corona images allow the USA to conclude there is indeed a missile gap, but in the other way around: the American missiles vastly outnumber the Soviet ones. In general, US intelligence reports become much more accurate and reliable, thanks to Corona.
• The KH-1 is quickly replaced by the KH-2 and then KH-3, also codenamed Corona. The KH-1 is the offspring of the CIA program satellite program; it is designed by the Itek Corporation and integrated by Lockheed.
• An U-2, flown by Gary Powers, is shot down over the Soviet Union. The pilot is captured by the Soviets. Overflights of the Soviet block are terminated, although the plane will still overfly other countries.

• The USA steps up its involvement in the Vietnam War.
• The Defense Intelligence Agency (DIA) is founded. As a Department of Defense agency, it focuses on military intelligence.
• The National Reconnaissance Office (NRO) is founded. Its mission is to oversee the development of the US reconnaissance program, and federate the efforts of the various military branches (Air Force, Navy, Army) and intelligence agencies (CIA, NSA, DIA). The early years of the NRO are marked with prolonged bureaucratic fighting between the Air Force and the CIA.
• The National Photographic Interpretation Center (NPIC) is founded. It regroups the CIA and military image interpreters under the same roof.
• First flight of a Samos E-1 satellite. The Samos program is managed by the Air Force and comprises several variants. The E-1 is a film readout system: the camera records an image on film, and then this film is developed while in orbit, scanned by an electronic system and the data is downlinked back to the ground. This makes the images available quickly, but severely reduces the number of images that the system provides, due to the limitations of the electronics. Resolution is 30m, improved to 6m in the E-2 model, but the coverage is limited. As a result, Samos is much less useful than Corona, and the stopgap Corona program becomes the backbone of US intelligence instead of Samos.

The KH-4B Corona (credit NRO)

• Cuban Missile Crisis. After discovering the USSR has installed intermediate range missiles in Cuba, the US blockades the island. A few days of extreme tension ensue, bringing the world at the edge of nuclear war, before the USSR agrees to withdraw the missiles (and the US withdraws missiles from Turkey).
• First launch of the KH-4 (still codenamed Corona). Compared the previous Corona modes, it carries two cameras, to take stereoscopic (3D) views of targets.
• First successful mission of a KH-5 Argon. The KH-5 is derived from the Samos E-4, and is used to make maps. The low resolution (140m) is compensated by the wide swath (550km). Only 6 successful missions will be carried out.
• First and last operational launch of a Samos E-5 film return satellite. The mission is a failure and no film is recovered. The camera, which comes down along with the film, is lost too.
• First launch of a DMSP (Defense Meteorological Satellite Program) weather satellite. One of the uses of the DMSP is to gather up-to-date cloud coverage information over the USSR, which is then used to avoid photographing overcast areas with the film reconnaissance satellites.  It is important as the film supply is limited, and shooting clouds wastes the mission potential.
• Last launch of a Samos E-2.

• First launch of a KH-6 Lanyard. The KH-6 was derived from Samos E-5, but out of the 3 launched only 1 successfully returned film. The resolution was around 1.8m (6 feet).
• First launch of the KH-7 Gambit 1. Gambit is higher-resolution than Corona, with a resolution of around 60cm (2 feet) but a lower coverage. It operates in tandem with it: Corona detects targets and areas of interest (it is consequently called a search system), Gambit is a surveillance system, used to precisely identify the targets, and measure their dimensions, in order to estimate the capabilities of new plane, missile or ship models. Gambit orbits between 110 and 280km, and uses 1.2m mirror. The KH-7 is designed by Eastman Kodak.

• Launch of Quill, an experimental radar satellite. Images are only acquired over the US, to assess the feasibility of radar imagery.

The KH-8 Gambit 3 (credit NRO)

• First launch of the KH-8 Gambit 3. Using a telescope of the same diameter as the KH-7, but with revamped optics and service module, the KH-8 has an extremely high resolution of reportedly up to 10 cm (4 inches). The exact resolution is still classified and as of 1984 was the highest ever achieved by satellite.

• Last launch of a KH-7.
• First flight of the A-12 Oxcart spy plane over North Vietnam. The A-12 flies at Mach 3 (around 3000 km/h), at around 25 000 m (80 000 feet), and is designed to have a low radar signature. These features enable it to fly over Vietnamese SAM sites with relative degree of safety. However, the Soviet SAM  sites use more advanced systems, so no overflights of the USSR are attempted.
• First operational use of a RB-57F spy plane with a direct readout infrared sensor. Previous generations recorded images on film, which could only be exploited after the aircraft had landed. The direct readout allows air crews to provided real-time intelligence, and to optimize their flight plan for more efficient collection.

The iconic SR-71

• First flight of the SR-71 Blackbird spy plane over North Vietnam. The SR-71 is an evolution of the A-12, but is an Air Force-run program, whereas the A-12 was CIA. The SR-71 carries a different sensor load from the A-12, including a side-looking Synthetic Aperture Radar, able to look though clouds.
• Last flight of the A-12.
• Prague Spring: the USSR invades Czechoslovakia. The invasion is so fast that by the time the satellite imagery is available, it is already over.

First flight over China of the D-21B hypersonic drone . The drone is launched from a B-52 bomber, flies at Mach 3 and records images on film. The film is then recover mid-air or at sea, like the film buckets from satellites. This first flight and the two other operational flights are failures and the program is cancelled.
The D-21A variant was supposed to be launched from a derivative of the SR-71, but was never deployed due to separation issues from the carrier plane.

The KH-9 Hexagon (credit NRO)

Launch of the first KH-9 Hexagon. A monster of a satellite, the KH-9, nicknamed “big bird”, is a search system combining the resolution of the Gambit-1 (60cm, 2 feet) with a very large swath (550km, or 300nm, wider than the KH-4). It is a film system, with the imagery returned in  4 separate recovery capsules. The exceptional coverage of the system is used to verify that the Soviets abide by the terms of the SALT-I arms limitation treaty. Two or more satellites are launched each year, to achieve semi-annual coverage of inhabited regions of the USSR and China, and annual coverage of the rest of those countries. To do this, the KH-9 uses two 0.5m cameras, performing stereo whiskbroom scanning over a 120° angle. Mission duration could extend up to 270 days, with altitudes typically between 130 and 290 km. The KH-9 is designed by Perkin-Elmer and integrated by Lockheed. It is initially a CIA program, and is then transferred to the Air Force.

• Last launch of a Corona, now replaced by the KH-9. By then the Corona series reaches model KH-4B, has seen its resolution improved to 1.8m (6 feet), and its swath reaches 280km (150nm). This was achieved using whiskbroom scan on the two cameras.
• The Defense Mapping Agency (DMA) is created.
• President Nixon announces the development of the Space Shuttle. The Shuttle is designed on the assumption that it will launch all US satellites, including NRO ones, and that the launch rate of these will keep increasing. The vehicle is consequently sized to be able to launch the KH-9 and its successors. Due to the unclassified nature of the program, NASA is not made aware that increased satellite reliability, and the move away from film systems, will drastically cut this rate in the future, and make the economics of the Shuttle untenable. To keep the manned space program going, the shuttle will also always carry a crew.

NRO program D, in charge of airborne reconnaissance, is abolished. The Air Force fully takes over this responsibility.

Fall of Saigon: the last US troops withdraw from Vietnam.

To-scale drawings of the US reconnaissance satellites (credit Guiseppe De Chiara). Note the precise layout of the KH-11 is speculative

• Launch of the first KH-11 Kennan, on a 300 x 500km orbit. It uses an electronic sensor instead of film, so the images can be downlinked to the ground in near real-time. These satellites have lifetimes of around 3 years, much longer than any of the film systems. In order to ensure the image downlink in near real-time, the first two data relay satellites, which form the basis of the SDS (Satellite Data System), are launched. Since the KH-11 flies higher than the Gambit, it carries a larger mirror in order to have a similar resolution. Mirror size is reported to be around 2.4m (7 feet 8 inches).
• Launches of KH-8s are reduced to 1 per year. Launches of KH-9s are also reduced to 1 per year.

First launch of the Space Shuttle.

• Launch of the first KH-11 block II satellite (name is speculative). Compared to the original KH-11, it orbits higher, in a 300 x 1000km orbit. These models also orbit for longer, spending up to 10 years in space.
• Last launch of a KH-8.

• Last launch of a KH-9, the rocket blows up shortly after liftoff.
• Space Shuttle Challenger blows up. The long time before return to flight convinces the NRO to avoid launching payloads on the Shuttle as much as possible. This, plus another launch failure in 1985, hits the NRO hard.

Lacrosse-5, imaged from the ground

First launch of a Lacrosse (later renamed Onyx) Synthetic Aperture Radar (SAR) satellite. SAR technology is very flexible, allowing high resolution or high coverage (but usually not both at the same time). It also does not depend on the Sun except for power, so it can image at night as well as during the day. The satellite is positioned to spend more time over regions of interests, compared to an optical satellite. It downlinks its data through the TDRS satellites owned by NASA.

The Berlin Wall falls, much to the surprise of every intelligence agency in the world.

• First Gulf War. Timely access to satellite imagery proves to be very difficult for the troops engaged. The NRO sets out to improve the delivery of tactical information to the end users.
• A mysterious payload is deployed by the Space Shuttle in a 62° orbit.  Nicknamed Misty by amateur observers, it is tracked for some time but then disappears. It is presumed to be a stealthy variant of the KH-11. Two other such satellites are launched over the years.
• The SR-71 is mothballed.

The USSR is dissolved. All nuclear weapons are repatriated to Russia in the following years. The Russian economy crashes, massively reducing the available military budget.

The existence of the NRO is declassified.

The Air Force launches the Evolved Expendable Launch Vehicle (EELV) program, to modernize its launchers and ensure a reliable access to space.

The NPIC, DMA, and parts of the DIA and of the NRO are merged to create the National Imagery and Mapping Agency (NIMA).

Ikonos (Digital Globe, USA)

• The development of the Future Imagery Architecture (FIA) is awarded to Boeing, after a competition with Lockheed. The FIA is planned to have both an optical and a radar component, to respectively replace the KH-11 and Lacrosse.
• Digital Globe, a private company, launches the Ikonos satellite. It is the first commercial satellite to collect 0.8m resolution images. Digital Globe provides commercial imagery to NIMA. Since it is not classified, it can be shared much more easily within the US government and with its allies.

The Treaty on Open Skies enters into force, 47 years after the idea was proposed by President Eisenhower. It allows 34 states, including Russia and the USA, to overfly the territory of other parties with mutually agreed on optical and radar sensors, with a 72 hour warning.

• Second Gulf War. Despite the tremendous capabilities of the reconnaissance program, the intelligence community finds evidence of a Weapons of Mass Destruction (WMD) program in Irak, which is used by President Bush as the basis for the invasion. The WMDs later turn out to be non-existent.
• NIMA becomes the National Geospatial-Intelligence Agency (NGA).

• Launch of the 5th and last Lacrosse.
• The optical component of the FIA is cancelled after significant cost overruns and delays by Boeing. Lockheed is contracted to build two new KH-11 while the US government decides what to do next.

Geoeye, another private company, launches the Geoeye-1 satellite, capable of collecting 0.41m resolution images. Geoye is also provides imagery to the NGA.
• Using an anti-satellite missile, the USA shoots down USA-193, a NRO bird launched in 2006 which failed upon reaching orbit. The satellite was in a curious 350 km orbit with a 58° inclination, giving it only a partial view of the globe. It was presumably a test for a new type of radar satellite.

After hesitating between developing lower-resolution but higher- coverage systems, and buying commercial satellites of the same class as Digital Globe and Geoeye, the US government decides to continue using KH-11s, with minimal improvements.

First launch of a satellite of the radar component of the FIA (FIA-R), codenamed Topaz.

The RQ-170 in Kandahar

• A RQ-170 stealthy reconnaissance drone crashes in Iran.
• Launch of a new generation of KH-11, the KH-11 block IV, built by Lockheed from the heritage of the pre-FIA program. Around that date, the KH-11 constellation is made up of a morning plane and an afternoon plane, each with a primary satellite and also, depending on the launches, a secondary satellite.

The NRO donates two 2.4m telescopes to NASA, presumably leftovers from the FIA program.

After the NGA announces it will be able to contract with only one commercial imagery provider from now on,  Digital Globe buys Geoeye.

The first pair of Geosynchronous Space Situational Awareness Program (GSSAP) satellites is launched. They provide an up-close and frequent look at the communication, early warning and electronic intelligence satellites of other nations in the geostationary belt. The GSSAP constellation will eventually have at least 6 satellites.

Planned date for the retirement of the U-2, as of 2017. It is to be replaced by high-altitude Global Hawk drones, carrying similar sensors.

Global Hawk sensor options
Northrop Grumman sensor options for the RQ-4B. From AinOnline



NRO Corona history

Eye in the Sky: The Story of the Corona Spy Satellites. Dwayne Day, Smithsonian History of Aviation and Spaceflight.


A sheep in wolf’s clothing: the Samos E-5 recoverable satellite. Dwayne Day, the Space Review. part I part II part III


Ike’s gambit: The development and operations of the KH-7 and KH-8 spy satellites. Dwayne Day, the Space Review. part I part II

NRO declassified Gambit records

NRO Gambit and Hexagon History, in particular Gambit and Hexagon Histories and CRITICAL TO U.S. SECURITY: The GAMBIT and HEXAGON Satellite Reconnaissance Systems


The flight of the Big Bird. Dwayne Day, the Space Review. part I  part II part III  part IV

Meeting the Challenge: The Hexagon KH-9 Reconnaissance Satellite. Phil Pressel, AIAA.

Phil Pressel’s blog on the KH-9

NRO declassified Hexagon records

NRO Gambit and Hexagon History, in particular Gambit and Hexagon Histories and CRITICAL TO U.S. SECURITY: The GAMBIT and HEXAGON Satellite Reconnaissance Systems

NRO Journal n°4


Flight of a feather: the QUILL radar satellite Dwayne Day, the Space Review.

Spy planes

NRO Journal n°5

The Wizards Of Langley: Inside The Cia’s Directorate Of Science And Technology. Jeffrey T Richelson.

Northrop Grumman Tests MS-177 Sensor on Global Hawk Bill Carey, AINOnline

KH-11 & SDS

The Inside Story of How Aviation Week’s Decision to Sit on One Cold War Blockbuster Led to Another Craig Covault, AmericaSpace

Top Secret KH-11 Spysat Design Revealed By NRO’s Twin Telescope Gift to NASA  Craig Covault, AmericaSpace

Gum in the Keyhole Dwayne Day, The Space Review

Relay in the Sky: The Satellite Data System Dwayne Day, Journal of the British Interplanetary Society

Spinning out of the shadows Dwayne Day, The Space Review


Radar love: the tortured history of American space radar programs   Dwayne Day, The Space Review

Space Shuttle

NRO Journal n°5

The spooks and the turkey: Intelligence community involvement in the decision to build the Space Shuttle Dwayne Day, The Space Review

Big Black and the new bird: the NRO and the early Space Shuttle Dwayne Day, The Space Review

Between the darkness and the light Dwayne Day, The Space Review

The HEXAGON and the Space Shuttle Dwayne Day, The Space Review

Black ZEUS: The top secret shuttle mission that never flew Dwayne Day, The Space Review

General Background

The leaked 2013 US intelligence budget, with many details about the NRO budget

What do users really want, anyway?

The Future of Earth Observation, Part II

Earth observation satellites do not come cheap. As mentioned in the previous post of this series, until a few years ago, they could cost a few hundred million dollars a piece to build and launch.  This makes satellite observation expensive, even for organisations that only buy the images. However, the end users are willing to spend that kind of money – 1.6B$ for commercial Earth Observation in 2014- because satellite imagery is the best way to address some specific needs. The aim of this post is list those needs, and explore what characteristics of satellite imagery are required to serve them.

Reliable intelligence

The historical use case of satellite imagery has been to gather extensive and objective intelligence on foreign countries. This has been the goal of the US reconnaissance program from the start of the Cold War, with a focus on China and the USSR. Satellites even became the only means to collect imagery deep inside the USSR after an U-2 reconnaissance plane was downed over the Soviet Union in 1960. Of course, imagery is not all. Intelligence can still be collected from human sources, using more traditional methods. But human intelligence has reliability issues: if no source can be found at the right place at the right time, then it is blind. If a source can be found nevertheless, it is not always a trustworthy one; history of full of double agents or outright liars who invent information.

An European Union Satellite Center intelligence note

Satellites, on the other hand, are cold and repeatable machines: they may not see everything, but they can see everywhere, and they do not produce fake images to further an agenda. As a result, they can provide objective, actionable intelligence: with its spy satellites, the USA could assess the military capabilities of the USSR, and especially the size of its armies. The images themselves are however only the starting point of an intelligence process: they are usually first turned into a briefing note by an analyst, then the information moves up the interpretation chain often by being correlated with other sources of information, and finally the finished intelligence product is distributed to decision makers.

In order to achieve this, high resolution imagery is necessary, to be able to precisely detect, identify and characterize objects such as planes, radars and ships. This means 1 pixel of the image has to correspond to a small distance on the ground, typically 1m of less, but smaller is better. Higher resolution enables to perform more challenging tasks, such as distinguishing between similar plane models, or estima. The US National Image Interpretability Rating Scale (NIIRS, available here) lists such tasks and the minimum resolution required.

Influence of resolution on the image content

A wide coverage can also be useful: the ability to collect images of most of the surface of a country, and not only a few places, reduces the chances of missing important information. This increases the confidence in the final intelligence product.

Example of the coverage (yellow) of 1 satellite for 1 day. Due to the limited field of view and the constraints of orbital mechanics, only part of the globe can be imaged.

Finally, a high revisit -having images of the same site every day for instance- makes it possible to catch transient events, and makes it harder to hide activity from the satellite. It also makes the interpretation of the activity easier.

Crisis management

Timely satellite imagery can be a powerful tool for crisis management. It can help track the progress of forest fires, assess the extent of floods and landslides, and evaluate the impact of industrial accidents. It can have military applications too, by detecting ships, ground troops, or airport activity, and assessing the impact caused by air strikes.

The key aspect in all these applications is latency: images have to be delivered quickly to the end-user once they have been acquired, or otherwise the information they contain will be outdated. Latency also has an impact on satellite tasking: the time between when an user makes an image request and when the request is uploaded to the satellite has to be low, or else the satellite can miss imaging opportunities.

Revisit is also important for crisis management: a short time between revisits means more imaging opportunities, and a more regular flow of information to the end-user. A single satellite can provide images of a given location every few days, but a constellation can give images every day, or even several times a day.

Resolution is needed for some tasks. For floods and landslides, the affected areas can be seen in low-resolution images, but for military or industrial assessments, high-resolution images are necessary.

Finally, georeferencing accuracy, that is, the ability to extract the exact GPS coordinates of a pixel in the image, is especially critical for military planning.

Agriculture and Mining

Satellite are also very useful to perform resource survey for crops or minerals. These applications mostly require a wide coverage, but not a high spatial resolution. However, they benefit from a high spectral resolution: different minerals in the ground give slightly different colours, which can be detected by a sensor able to finely distinguish between light wavelength. Such a sensor is called a multispectral sensor. Whereas standard sensors typically capture only red, green and blue channels, a multispectral sensor can capture much more colours, starting from the near infrared (to detect crops), and extending in the thermal infrared.

The multispectral channels of the Worldview 3 satellite


Mapping used to require long ground surveys or more recently, aerial surveys. Now part of the job can be accomplished by satellites. It is another area where coverage is key, along with accurate georeferencing: with an accurate 3D location of all points of the image, a digital elevation model can be build, which can help infrastructure planning, or low-altitude flight planning .

Economic monitoring

Economic monitoring is a civilian version of the intelligence use case, with the goal to objectively and frequently measure the economic activity  of a region. It includes applications such as monitoring oil reserves (by measuring the volume of oil tanks) or store attendance (by counting cars in parking lots)

Oil  tank volumes, measured by Orbital Insight

To capture quickly-evolving event such as these, a moderate resolution (~1m) and a very high revisit rate are needed, because store attendance for instance depends a lot on the time of day.

The Future of Optical Earth Observation

Part I: The road so far

Commercial Earth observation is undergoing rapid changes: much like rocket companies such as SpaceX, Blue Origin and a handful of others are challenging the established players in the launch industry, new ways of doing things are being introduced by “new space” companies in the commercial Earth Observation business. Can they compete with, and eventually replace the traditional satellite builders and operators? Or will they address different markets and coexist? In this series of posts, I will give my analysis on where I think this industry is going, starting with this first entry on the history of commercial optical earth observation.

The beginnings

To understand better what is changing in satellite earth observation, let’s first look back to where it came from.

Optical earth observation satellites have existed since 1959, just two years after the first artificial satellite reached orbit. That year, the USA launched Vanguard 2, the first weather satellite. It carried an optical scanner to study cloud cover, and sent its images back to Earth through radio link. It started a long line of American weather satellites, leading to today’s NOAA satellites. However, the images collected by these systems do not provide much detail: even today, they have resolutions of a few hundred meters. This is fine for meteorology but not for other uses.

The same year Vanguard 2 was launched, the USA also launched the first spy satellites. Several generation were developed, starting with the Corona program. These satellites used a film system to capture the images. The films were then stored in a recovery capsule, after which the capsule was deorbited and recovered. The advantages of using film together with large optics were the high resolution of the images, which was measured in feet, and the removal of the storage and transmission electronics. This design choice however resulted in a relatively long time between the acquisition of the image and its delivery, and required a high launch cadence and complex recovery operations. The USSR had a similar program of film-based reconnaissance satellites.

Drawing of the Corona film reconnaissance satellite

The imagery produced by the spy satellites remained classified, and so did most of their technology. In the USA, NASA even had an agreement with the Department of Defense not to develop sensors with better than 20 meter resolution. Nevertheless, civilian medium-resolution satellites were eventually developed, using electronic sensors and radio downlink of images.

At first, these systems, such as the first satellites of the American Landsat program, could only provide images with resolutions in the tens of meters. They were best suited to mapping and agricultural uses. The Spot 1 satellite, launched in 1986 by the French, was the first satellite providing commercial imagery at 10m resolution. Two month after its launch, it took a picture showing the damaged nuclear reactor at Chernobyl, confirming the explosion and the usefulness of timely,  higher-resolution commercial imagery.

The Landsat and Spot programs were still cutting-edge technology at the time, leading to high costs. However, the developments in electronics made them affordable for the civilian space programs of industrialized nations. The satellites themselves were heavy -around 2t-, and had limited resolution, especially when compared with airborne imagery. They also had limited agility, meaning they could point in a direction to take an image, but not repoint quickly in another direction to take another image. Still, they found a market, leading to the launch of improved commercial satellites, with a new design, in the 2000s.

Current state of the industry

Encouraged by the success of Spot, and by the fact the Russian started selling high-resolution images from their military film-based systems in the early 90s, many countries developed even higher-resolution civilian satellites. The USA passed the Land Remote Sensing Policy Act in 1992, which allowed private US companies to operate earth observation satellites.  This led to the creation of DigitalGlobe and GeoEye. Starting from the late 90s, the two companies launched several high-resolution, high-agility satellites, eventually offering 50 cm imagery on the commercial market, and even higher-resolution to the Pentagon. This regulatory limit on resolution was progressively relaxed over the years, to keep the US industry competitive with foreign companies.

Several countries followed suit. As the satellite pictures at the top of this paragraph show, they adopted similar solutions to solve the same problem: all those satellites have relatively large telescope apertures to provide high resolution images, but are very compact to be able to quickly repoint themselves to take another image. The pointing agility is a critical feature of these designs, because high-resolution telescopes have a low field of view: they can only produce images which are around 15 km wide. So to image two places located in the same region but more than 15km apart, they have to repoint and  take a new image. The faster they can repoint, the more interesting places they can image, and the more value they generate.

The technology required to build these satellite still made them expensive, coming at a few hundred millions dollars a piece, but made them more accessible than the previous generation.  Several countries, such as South Korea, Israel, India and the UK, joined the club of high-resolution satellite manufacturers. A dynamic export market emerged and is still growing, as countries and companies without the technology to build such a satellite bought one from a foreign manufacturer.

Looking ahead

Thanks to the advances in electronics miniaturization, the barrier to entry in the satellite design and manufacturing business has been greatly reduced. New entrants, such as Terra Bella (formerly Skybox Imaging), Planet Labs, and BlackSky Global have launched observation satellites, or announced they will do so. In order to better understand what kind of market they aim for, the next post will focus on the different uses of satellite imagery.