Design
It is believed to resemble the Hubble Space Telescope in size and shape, as the satellites were shipped in similar containers. Furthermore, a NASA history of the Hubble, in discussing the reasons for switching from a 3-meter main mirror to a 2.4-meter design, states: "In addition, changing to a 2.4-meter mirror would lessen fabrication costs by using manufacturing technologies developed for military spy satellites." A CIA history states that the primary mirror on the first KH-11s measured 2.34 meters, but sizes increased in later versions. NRO led the development of a computer controlled mirror polishing technique, which was subsequently also used for the polishing of the primary mirror of the Hubble Space Telescope.
Assuming a 2.4-meter mirror, the theoretical ground resolution with no atmospheric degradation and 50% MTF would be roughly 15 cm (6 inches). Operational resolution would be worse due to effects of the atmosphere. Different versions of the KH-11 vary in mass, with earlier blocks ranging from 13,000 to 13,500 kilograms, whilst later blocks have a mass of around 19,600 kg. Its length is believed to be 19.5 meters, and diameter is 3 meters or less.
The two optical telescope assemblies (OTAs only, not full satellites) offered to NASA from the NRO in January 2011 are suspected, but not confirmed, to be KH-11 series "extra hardware." The OTA's are of a three-mirror anastigmat (TMA) optical design (sans the 3rd "tertiary" mirror). The f/1.2 primary has a diameter of 2.4 m, and is refocused by the secondary to give an overall f/8 focal ratio, making the optical telescope assembly shorter than that of HST. With the addition of the tertiary mirror, this will produce a much wider field than Hubble's 2-mirror f/24 Ritchey–Chrétien optical design, making it an potential ideal observatory for Dark Energy or other astrophysics surveys. The secondary mirror is mounted on a hexapod to increase the side-viewing and ground scanning ability for the originally intended reconnaissance mission.
KH-11 was the first reconnaissance satellite equipped with charge-coupled device (CCD) array technology for imaging which had a resolution of 800 x 800 pixels. Later block satellites may include signals intelligence capabilities and greater sensitivity in broader light spectrums (probably into infrared).
Later satellites had larger mirrors, with a diameter of around 2.9–3.1 m. Jane's Defence Weekly indicates that the secondary mirror in the Cassegrain reflecting telescope system could be moved, allowing images to be taken from angles unusual for a satellite. Also, there are indications that the satellite can take images every five seconds.
Four generations of U.S. electro-optical reconnaissance have been identified:
Read more about this topic: KH-11 Kennan
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