The KH-4 (Keyhole-4) was fourth version in the Corona-program to build an optical reconnaissance satellite. Only the first two satellites were launched under the name Discoverer, before this designation was dropped.
The KH-4 payload introduced a second camera to provide stereoscopic imaging. The Corona-M or Mural camera consisted of two C''' (Corona triple-prime) cameras inherited from KH-3. The cameras were mounted with 30 degrees separation angle. The two cameras are referred to as fore (for forward looking) and aft (for rear looking). KH-4 also carried a 4 cm index camera, with a focal length of 38 mm, a ground resolution of 162 m, and frame coverage of 308 km × 308 km. The Film was returned by a single General Electric return vehicle (SRV, Satellite Return Vehicle). The Mural-camera was built by Itek Corporation and had a ground resolution of 7.5 m.
The satellite was based on the Agena-D upper stage, which provided attitude control in orbit. The film return capsule carried its own small solid-fuel retro motor to deorbit at the end of the mission with mid-air recovery of the returning capsule by a specially equipped aircraft.
Earlier KH-4 missions were based on the Agena-B stage.
Secondary Payloads
Some missions featured piggy-back payloads, which remained connected to the Agena-D stage.
- KH-4 7 carried the Taki 2 (Aftrack 23) ELINT payload (?) and the GRD-N-Payload No. 4 (HSRP 8)
- KH-4 10 carried an Aerospace Corp Package (Starfish package ?)
- KH-4 11 carried the RM 3 radiometer payload for background measurements for the MIDAS program
- KH-4 13 carried the RM 4 radiometer payload (identical to RM 3) for background measurements for the MIDAS program
- KH-4 16 carried the Red Vino 1 (Aftrack 28/Mission 7203) ELINT payload
- KH-4 17 carried the Taki 3 (Aftrack 29/Mission 7204) ELINT payload and the Aerospace 4-Color TAEP for the MIDAS program
- KH-4 18 carried the New Jersey 2 (Aftrack 30/Mission 7205) COMINT payload
- KH-4 19 carried the Red Vino 2 (Aftrack 31/Mission 7206) ELINT payload and the LPARL Aurora 1963a Research Module
- KH-4 21 carried the Wild Bill 3 (Aftrack 32/Mission 7207) ELINT payload to search for signals from the HEN HOUSE ABM/AES radar at Sary Shagan and the EROS reflector experiment
- KH-4 24 carried the RM 5 radiometer payload for background measurements for the MIDAS program
- KH-4 25 carried the Long John 2 (Aftrack 35/Mission 7219) ELINT payload
- KH-4 26 carried the Long John 1 (Aftrack 36/Mission 7218) ELINT payload
Two missions carried small satellites into orbit.
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