Now you have almost certainly heard of the recently released high-resolution satellite image that showed after Iran's failed attempt to launch their Sapphire liquid fuels rocket. The geopolitical ramifications of Iran developing this type of ballistic missile technology is indeed a curious story in itself, but in this case there has been much greater interest in how the picture was taken. Given known variables such as the time and date of the incident and the location of the launch pad, analysts have determined that it was probably taken by a classified US KH-11 satellite.
The picture is truly striking and shows a level of detail that far exceeds what is available through any of the space observer's services that we as civilians have access to. Estimated to have been taken from a distance of about 382 km, the image appears to have a resolution of at least ten centimeters per pixel. Given that the satellite in question drops as low as 270 km at its closest proximity to the Earth's surface, it is likely that the maximum resolution is even higher.
Of course, there are many aspects of the KH-11 satellites that remain highly classified, especially with regard to recent hardware reviews. But their existence and general design have been common knowledge for decades. Images taken from earlier generation KH-11 satellites leaked or were otherwise released during the 1980s and 1990s, and although the Iranian image is indeed of higher faith, this is not entirely surprising given the intervening decades.
What we know a lot less About are the monitoring assets for tracks that replace KH-11. The satellite that took this image, known by its designation USA 224, has been in orbit since 2011. The National Reconnaissance Office (NRO) has launched a number of newer spacecraft since then, with several more scheduled to be lifted into orbit between now and 2021.  So let's take a closer look at the KH-11 series with reconnaissance satellites and compare it to what we can share about the next generation or spying technology for orbits that are already orbiting overhead.
Secret Agent Hubble
The KH-11 “KENNEN” satellite was designed as a replacement for the film-based KH-9 “HEXAGON” satellites developed in the 1960s. Restoring images from these older satellites required the use of small capsules that would re-enter the Earth's atmosphere and get trapped in the air by a waiting aircraft; a slow, complex and expensive process. By comparison, KH-11's digital technology meant that images could be transmitted via a network of communications satellites in near real-time.
But despite the first KH-11 being launched all the way back in 1976, there has never been a published image of one. Fortunately, analysts have a pretty good idea of what the satellites look like because they happen to have a very famous cousin: the Hubble Space Telescope. Both space-traveling Cassegrain reflector telescopes were built by Lockheed, and according to official NASA data, some of the design elements of Hubble (such as the main mirror's 2.4 meters in diameter) were selected to "reduce manufacturing costs with manufacturing techniques developed for military spy satellites. ”
The family's equality is not just speculation either. In 2010 and again in 2015, astrophotographer Ralf Vandebergh was able to directly image two separate KH-11 satellites with mainly hobbyist class equipment. Despite his relatively low-tech approach, he was able to snap pictures of these secret spacecraft that seem to confirm suspicions that their design is similar to Hubble.
In the pixilated 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 has at least one solutione like Hubble, and potentially a directional antenna set of some type on the opposite side; although Ralf says that this can simply be a trick to the light.
In terms of size, the KH-11 is almost certainly the same diameter of the Hubble due to the split mirror, but rumors suggest it is not that long. A shorter focal length would give the KH-11 a wider field of view than Hubble, which would be better suited for observing the ground.
As good as it gets
If a man with consumer equipment was able to identify, track and photograph two KH-11 satellites, it has been argued that intelligence agencies in other countries have succeeded with similar features. The idea that any technologically advanced nation would be caught unaware of the presence of one of these satellites overhead seems unlikely at best.
Of course, knowing that they are up there is not the same as knowing what they can actually see. But as it turns out, it's not a difficult question to answer either. Calculation of the angular resolution of a telescope can be done using the Rayleigh criterion, which takes into account the wavelength to be observed and the diameter of the lens aperture. The angled resolution, combined with the altitude of the satellite at the time of observation, can tell us how large an object must be before an optical telescope like KH-11 can actually see it from space.
With a 2.4 m mirror observing a nominal wavelength of 500 nm, the Rayleigh criterion states that a telescope should have a diffraction limited resolution of about 0.05 arcs. At a height of 250 km, this means a surface resolution of about 6 cm. Remember that this is a theoretical maximum, in practice the resolution will be smaller due to atmospheric instability and it is likely that the satellite is probably not directly above the target. Therefore, with an estimated resolution of 10 cm, the Iranian image is well within the calculated performance envelope for KH-11.
Again, it would not have been difficult for any potential opponent to run the numbers and realize what KH-11 could see. Especially since the United States has been running surveillance satellites with this physical resolution limit for more than 50 years. The KH-8 "GAMBIT", a movie-based surveillance satellite that was first launched in 1966, was also capable of resolving objects 5 to 10 cm under ideal conditions.
The Next Generation
It may seem strange that a 1966 United States surveillance satellite would have comparable resolution to those flying around 2019, especially with how much technology has changed since then. But in the end, these are large optical telescopes, and the physics that guide their performance were calculated long before anyone ever dreamed of sending one of them to space. The rest of the spacecraft surrounding the telescope has certainly evolved since the 1960s with improved propulsion, data flow, energy consumption and endurance; but a 2.4 m mirror will work in the same way today as it did 50 or even 100 years ago.
If the functions of optical telescopes have hit the physical boundary, where do we go from here? The most obvious way to rotate more performance from these satellites is by using image enhancement software. Thanks to hopes and limits, computer performance has made over the past decade, the images from the telescope can be sharpened and digitally cleaned. This is potentially why the Iranian image looks clearer than the KH-11 images released during the 1990s, even though the true resolution of the telescope has not fundamentally changed. launched in January 2019, can amplify or completely replace their optical telescopes with other sensing techniques such as synthetic aperture radars (SARs). A radar imaging satellite has many advantages over an optical, such as the ability to observe the target at night and in bad weather. In laboratory settings, SAR has reached sub-millimeter resolution, and although the true accuracy would certainly be lower when looking at the target from hundreds of miles away, it has the potential to move orbital monitoring beyond the physical limits that have existed since the very first "spy satellites" took get to heaven during the Cold War.