The KH-11 series of reconnaissance satellites, also known by their Byeman code names Kennen (the often reported "Kennan" is a misspelling) and Crystal (since 1982), are the first American spy satellites to utilize electro-optical digital imaging, and provide a real-time optical observation capability. They replaced the earlier film-return type satellites of the KH-8 Gambit-3 and KH-9 Hexagon series.

The satellites are believed to use a 2.4 m diameter prime mirror, which gives a theoretical ground resolution of 15 cm. Operational resolution would be worse due to effects of the atmosphere. The eartly satellites likely use photo-diode detctors, later CCD detectors were used for imaging. Reportedly some ELINT equipment is also carried. Prime contractor for the KH-11 satellites is Lockheed (now Lockheed Martin).

The KH-11 series transmit their data via relay satellites called Satellite Data System (SDS-1, SDS-2, SDS-3), which operate in Molniya orbits and geostationary orbits.

The KH-11 satellites were built in several blocks, each introducing improvements. The optical system remained probably mostly unchanged, while sensors and avionics have been improved. With the advent of the more powerful Titan-4 launch vehicle, the amount of fuel has likely been increased for a longer lifetime. The identification of the blocks is tentative and based on the orbital behavior and launch vehicle versions.

Block 1 (KH-11 1-5): Original version; ~270 × 500 km orbit

Original version; ~270 × 500 km orbit Block 2 (KH-11 6-9): Improved infra-red capabilities, higher apogee ~270 × 1000 km orbit

Improved infra-red capabilities, higher apogee ~270 × 1000 km orbit Block 3 (KH-11 10-12, 14): Improved Metric CRYSTAL System" (IMCS), which adds reference markings for accurate mapping to images obtained by the satellite; more fuel for longer life time; built for Space Shuttle deployment and servicing; used 62 ft fairing with TPA (Titan Payload Adaptor) on Titan-4

Improved Metric CRYSTAL System" (IMCS), which adds reference markings for accurate mapping to images obtained by the satellite; more fuel for longer life time; built for Space Shuttle deployment and servicing; used 62 ft fairing with TPA (Titan Payload Adaptor) on Titan-4 Block 4 (KH-11 13, 15-16): Possibly part of EIS (Enhanced Imaging System); Space Shuttle related equipment removed; used 66 ft fairing without TPA (Titan Payload Adaptor) on Titan-4

Possibly part of EIS (Enhanced Imaging System); Space Shuttle related equipment removed; used 66 ft fairing without TPA (Titan Payload Adaptor) on Titan-4 Block 5 (KH-11 17,18): Possibly a further upgraded version. The first of those satellite was launched to an unusual 74° orbit, so it might be something else, perhaps a stealthy Misty variant.

The satellites of Block 3 and 4 are hence often dubbed "advanced Crystal". Likely the often reported designation "KH-12" is not correct and they are likely also called KH-11. The Byeman code name Ikon has been reported for this series.

The 8X or EIS program was planned as a replacement, but was finally cancelled due to escalating costs. Otherwise, the Block 4 version is part of EIS.

The FIA optical satellites were designed as their successors, but with continuing delays and finally the collapse of the FIA optical program, two more satellites were procured. Apparently the production has restarted for more satellites.

During development, the Byman code name Zaman was used until 1971, when it was replaced by Kennen. In 1982 it was again changed to Crystal.

The relation to the stealthy Misty satellites is unclear, but Misty might be derived from the KH-11 design.

The KH-11 17 (NROL 71) launch is tentatively assigned to this series, but features a 74° orbital inclination. It might be either a new orbital regime introduced with Block 5 or the satellite might be a new type.

Note: The NROL designations refer to the launch, not to the payload.