(Military) Space Telescopes / Keyhole
Keyhole (KH-11) satellites have always been of special interest because of their proposed similarity to the Hubble Space Telescope (HST). The big difference is that Keyholes are military satellites and that they are used for Earth observation instead of space research. For astrophotographers interesting is the fact that the orbits of most Keyhole satellites are highly elliptical. This means that they sometimes can be observed during relatively low passes above the Earth, increasing the chance to capture detail.
First Detail Images USA-276 (NROL-76)
Launched into a 50 degrees inclined orbit of 377x389 km, USA-276 raised question marks among satellite observers around the world. Especially because of the unusual orbital inclination compared to that which is normally used for newer type KH-11 satellites, suspicions arose that USA-276 could be a completely new Keyhole design or satellite type.
On March 30, 2021, USA-276 was captured in good seeing conditions during a 66 degrees pass through the South, from a range of 425 km. The following images compare USA-276 to earlier images of USA-129 and USA-245, both reconnaissance satellites of the type KH-11 (KENNEN). The strong similarities between visible details between these images, a.o. telescope bus and propulsion module / equipment section (fainter / brighter components) and visible (solar) panels suggest in this observation that USA-276 could be still a KH-11 type satellite as well or a type with strong similarities to a KH-11 design.
Telescopic images of Keyhole satellites show in general a typical character and typical details in the raw frames that, distinguishes itself from other satellites. This can only be determined by a lot of experience in telescopic high resolution imaging of this class of satellites.
Sequence of frames from the 2021-03-30 session shows USA-276 'growing' bigger while approaching. The image scale shows 2,3 arcseconds on the frames.
Even the smallest images of the session are bigger then 2 arcseconds, well beyond the theoretical resolution of a 10 inch telescope and clearly show shape
Launched in 2019, USA-290 went into a 74 degrees inclined orbit of 395x420 km. Because this orbital inclination is different then the 98 degrees inclination that generally is used for KH-11 class satellites, and additionally it's of a less elliptical type and also the orbit is not sun-synchronous - characters that are also common for new type KH-11 satelllites, experts believed that USA-290 could possibly be a new type of (KH-11) satellite.
USA-290 was captured on March 30, 2021 during a 48 (WNW) pass in favorable seeing conditions from a range of 551 km. The relatively long range caused that the images are not of the best quality but a good efficiency of usable frames was obtained, which still enabled a qualitative image analyses. Images below are a selected single frame (left) and an average of 14 stacked frames (right). The visible details suggest that USA-290 could still be a KH-11 type of satellite or a design that is close to a KH-11 satellite.
The Keyhole satellites are a family of reconnaissance satellites launched by the US National Reconnaissance Office (NRO) since the mid-seventies. They are known under different code names, but often named Evolved Enhanced CRYSTAL (EEC). Observers recognize them mostly as KH-11 KENNAN satellites. The later versions are actually newer types often classified as KH-12 or Advanced KENNEN or Improved Crystal. It is often said that the Keyhole satellites are similar to the Hubble Space Telescope. According to sources they were shipped in similar containers and a NASA history stated that they used military Keyhole technology in the Hubble to minimize costs. In 2011, NRO offered NASA two surplus Keyhole satellites. On that occasion, NASA engineers were able to visit the KH-hardware. It was reported that the focal length of the Keyholes was shorter then that of the Hubble. The shorter telescopes enabled the military to oversee larger areas on Earth. Though, it is not clear if these donations were original KH-11 telescopes or upgraded versions, originally intended for the cancelled FIA-program. This gain of the Keyholes over the astronomical Hubble was interesting for NASA as it could assist research in different astronomical fields. In 2010, I managed to photograph some of the Keyhole satellites in rare favorable occasions.
The image below shows the KH-129 satellite captured on September 4, 2010 from a range of 336 kilometers, taken during a pass not far from the lowest point of the orbit of the satellite, even below the orbit of the International Space Station. The image is presented in both positive and negative. The model on the right features a proposed presentation of the telescope main shape, without the solar panels.
On the left we see the actual image taken with a 10 inch aperture telescope, on the right we see one of the proposed models developed by insiders. There seem to be incredible similarities. Note especially the thicker bright part of the telescope-tube below. Also some segments in the tube appear to be visible. Interesting are some elements that are mounted on the satellite that could be satellite dishes or solar panels. The biggest difference from the model is the big structure on the right side of the tube that is most likely a solar panel. Although the smaller structure on the left side of the tube suggests something like a dish antenna, it is probably the other solar panel. Other images taken a day later with the same setup under different circumstances seems to confirm the second solar panel. This and other images of the KH-129 also suggest an aperture door like on the Hubble. This is the structure visible on top of the image but it could also be some other element that we not know.
These are the first known detail images of USA-245, at the time of writing, the most recent Keyhole spacecraft in the program captured with a 25 cm telescope on August 5, 2015 near perigee from a distance of 289 kilometers while it was 277 kilometers above the ground. At the time of imaging, the satellite had been in space for almost 2 years. In these images, different elements such as the telescope tube and the thick compartment for the instrument bay can be clearly seen. The thicker instrument unit appears bright in nearly all ground based images of Keyhole satellites. Also, there is a hint of solar panels. USA-245 or NROL-65 was launched from Vandenberg Air Force Base at 18:03 UTC (11:03 local time) on 28 August 2013.
Comparing these USA-245 observations with those of USA-129 earlier on this page, shows many similarities in visible detail.
Processings of USA-245 images on August 5, 2015. The different parts of the telescope tube are well recognizable
Processing of one of the USA-245 frames taken on August 5, 2015 that clearly shows an indication of visible solar panels or other types of panels
KH-11 General Brightness Pattern
Below: The typical flare during passes of KH-11 satellites in general 97 degrees inclined sun-synchronous orbits is apparently caused by a reflection in the highly reflective propulsion section of the satellite as these unprocessed raw frames of the USA-245 imaging session on August 5, 2015 show.
Below: Explanation of the different sections visible in telescopic images based on Wikipedia document 'Conceptual drawing based upon HST layout'
KH-11 (Keyhole) satellites seem to show in all these observations at least clearly a longer thinner part and a shorter thicker part. The longer thinner part apparently is the telescope tube comparable to the Hubble Space Telescope. The thicker part is apparently the propulsion module at the rear end that shows up bright in images, indicating that this is a highly reflective element. The thicker part seems clearly flanked by elements that appear to be solar panels or antennas but their visibility depends on observing conditions like angle and illumination.