KH-8 (Keyhole-8) or Gambit-3 was the second generation of Gambit high resolution reconnaissance satellites. The KH-8 Block 2 were the second iteration of this design, introducing a second reentry vehicle.
KH-8 had the same basic layout as the KH-8 (Block 1) series. The forward part was joint via a roll joint with the Agena-D. The major subsystems of the satellite included a photographic-payload section (PPS), a satellite-control section (SCS), and the booster vehicle. The payload section contained a camera module and two satellite recovery-vehicle (SRV). The control section included the command system, the orbit-adjust module, an attitude-control subsystem, a back-up stabilization system (BUSS), and the power supply.
The next 14 satellites of the KH-8 Block 2 series (KH-8 23 to 36) featured two SRVs.
The camera system was strip camera coupled to an optical system a focal length of 4.46 m. In the optical system the ground image is reflected by a steerable flat mirror to a 1.21 m diameter stationary concave primary mirror. The primary mirror reflects the light through an opening in the flat mirror and through a Ross corrector. At perigeum, the main camera imaged a 6.3 km wide ground swath on a 223.8 mm wide moving portion of film through a small slit aperture. The ground resolution was as small as 0.1 m or better, near the theoretical physical e resolution limit imposed by atmospheric turbulence.
The Astro-Position Terrain Camera (APTC) contained three cameras: a 75 mm focal length terrain frame camera, and two 90 mm focal length stellar cameras. The terrain frame camera takes exposures of Earth in direction of the vehicle roll position for attitude determination. The stellar cameras observed in 180° opposite directions and took images of star fields.
This series introduced the improved Titan-3(23)B Agena-D launch vehicle. The last five used the stretched Titan-3(24)B Agena-D version.
On KH-8 25, the recovery of the second SRV failed. KH-8 27 suffered a failure of the command system and the second SRV was not recovered. KH-8 35 was lost due to a pneumatic regulator failure during ascent.
The KH-8 Block-2 satellites were succeeded by the improved KH-8 Block 3 satellites featuring a new high performance roll joint.
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