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You have almost certainly heard of the recent publication of a high-resolution satellite image showing the consequences of Iran's unsuccessful attempt to launch its Safir liquid fuel rocket. The geopolitical ramifications of the development of this type of technology by ballistic missiles by Iran are certainly new newsworthy, but in this case, we are much more interested in the way in which the photo was taken. . Given known variables such as the time and date of the incident and the location of the launch pad, analysts determined that it was probably taken by a US satellite ranked KH-11.
The image is certainly striking, it shows a level of detail that far exceeds what is available in all the space observation services we have access to as civilians. Estimated to have been taken at a distance of about 382 km, the image appears to have a resolution of at least ten centimeters per pixel. Since the orbit of the satellite in question has an inclination as low as 270 km at the approach closest to the Earth's surface, it is likely that the maximum resolution is even higher.
Of course, many aspects of KH-11 satellites remain highly classified, especially with regard to the latest hardware revisions. But their existence and general conception have been well known for decades. Images taken with earlier generation KH-11 satellites were disclosed or published in another way in the 1980s and 1990s, and although the Iranian image is certainly of greater significance. fidelity, this is not totally surprising considering the past decades.
What we know a lot less about is the orbital surveillance that replaces the KH-11. The satellite that took this image, known as USA 224, has been in orbit since 2011. The National Reconnaissance Office (NRO) has launched a number of new spacecraft since, and several more will be put into orbit from here to today. 2021.
So let's take a closer look at the KH-11 reconnaissance satellite series and compare it to what we can muster about next generation technology or orbital espionage already possible.
Hubble Secret Agent
The KHEN-11 "KENNEN" satellite was designed to replace the KH-9 "HEXAGON" satellites based on films developed in the 1960s. The recovery of images from these older satellites required the use of small capsules that would penetrate again in the atmosphere of the Earth and would be caught in the air by a plane waiting; a slow, complex and expensive process. In comparison, the KH-11's digital technology was able to transmit images through a communications satellite network in near real-time.
Despite the launch of the first KH-11 in 1976, no image of the latter was made public. Fortunately, analysts have a pretty good idea of what satellites look like because they have a very famous cousin: the Hubble Space Telescope. Lockheed built the two Cassegrain reflector telescopes going from space. According to NASA's official records, certain Hubble design elements (such as the 2.4-meter diameter of the main mirror) were selected to "reduce manufacturing costs by using manufacturing technologies." developed for military espionage satellites ".
Family resemblance is not speculation either. In 2010 and again in 2015, astrophotographer Ralf Vandebergh was able to directly image two separate KH-11 satellites with the aid of an essentially amateur-grade equipment. Despite his relatively untechnical approach, he has managed to photograph these secret spacecraft that seem to confirm the suspicions that their design is very similar to that of the Hubble.
On pixelated images, we can see the same tapered shape and what appears to be an opening door at the end of the telescope. The KH-11 also features at least one solar "wing" like the Hubble and possibly a network of directional antennas on the opposite side; Even if Ralf says it could just be a sleight of hand.
In terms of size, the KH-11 is almost certainly the same diameter as the Hubble because of the shared mirror, but rumors suggest it's not as long. A shorter focal length would give the KH-11 a wider field of view than Hubble, which would be better for viewing the ground.
As good as that
If a man equipped with mainstream equipment could identify, track and photograph two KH-11 satellites, it goes without saying that intelligence agencies in other countries have managed to do the same. The idea that any country at the forefront of technology would be surprised by the presence of any of these satellites above its capacity seems at best improbable.
Of course, knowing that they are up there is not the same as knowing what they can actually see. But it turns out that it is not a difficult question to answer either. The calculation of the angular resolution of a telescope can be made using the Rayleigh criterion, which takes into account the wavelength to be observed and the diameter of the aperture of the lens. This angular resolution, when combined with the altitude of the satellite at the time of observation, can tell us the size that an object must have to be reached before a Optical telescope like the KH-11 can actually see it from the space.
With a 2.4 m mirror observing a nominal wavelength of 500 nm, the Rayleigh criterion tells us that a telescope should have a resolution limited to diffraction of about 0.05 seconds d & # 39; arc. At an altitude of 250 km, this translates into a surface resolution of about 6 cm (2.4 inches). Do not forget that it is a theoretical maximum. In practice, the resolution will be lower due to atmospheric instability and the fact that it is unlikely that the satellite is directly above the target. With an estimated resolution of 10 cm, the Iranian image is therefore well within the KH-11 calculated performance envelope.
Once again, it would not have been difficult for a potential opponent to know the numbers and realize what the KH-11 would be able to see. Especially since the United States has been using surveillance satellites at this physical resolution limit for more than 50 years. The KH-8 "GAMBIT", a filmed surveillance satellite first launched in 1966, was also able to solve objects from 5 to 10 cm under ideal conditions.
The next generation
It may seem odd that an American surveillance satellite of 1966 has a resolution comparable to that of its 2019 satellites, especially in view of the evolution of technology. But in the end, these are large optical telescopes, and the physics that governs their performance has been understood long before anyone has ever dreamed of sending one into space. The rest of the space shuttle surrounding the telescope has certainly evolved since the 1960s, with improved propulsion, data processing capability, energy consumption and endurance; but a 2.4 m mirror will function in the same way as 50 or even 100 years ago.
If the capabilities of optical telescopes have reached their physical limit, where are we going now? The most obvious way to get more performance out of these satellites is to use image enhancement software. Thanks to the considerable progress made by computer performance over the past decade, telescope images can be refined and digitally cleaned. This is potentially why the Iranian image seems clearer than the KH-11 plans published in the 1990s, even though the actual resolution of the telescope has not fundamentally changed.
Beyond that, it is thought that the new reconnaissance satellites, such as the NROL-71 launched in January 2019, could complement or completely replace their optical telescopes with other detection technologies such as synthetic radar. Opening (SAR). A radar imaging satellite has many advantages over an optical satellite, such as the ability to observe the target at night and in bad weather. In the laboratory, SAR resolution reaches a resolution of less than one millimeter, and although the actual accuracy would certainly be lower if the target was seen hundreds of kilometers away, it could potentially displace orbital monitoring beyond existing physical boundaries. since the very first "spy satellites" took flight during the Cold War.
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