Samos-E4

Samos-E5 [USAF]
Samos-E4 similar

Satellite and Missile Observation System), originally named Sentry, was the second program that evolved from WS 117L and aimed at developing a heavier reconnaissance satellite that would be launched by an Atlas booster instead of the Thor used to launch the project Discoverer (Corona).

Samos E-4 was a film-return mapping payload for the USAF Aeronautical Chart and Information Center. It would have used the return capsule of the Samos E-5 high resolution satellite. The mapping camera had a 15.2 cm focal length with a f/5.6 lens and the stellar indexing camera had a 7.6 cm focal length. From a 145 km perigee, the ground resolution would have beenn on the order of 45 m.

Four payloads were produced, but they were put in storage and never flown. The E-4 program was cancelled and replaced with the concurrently developed KH-5 Argon, a mapping payload in the Corona program.