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Samos (Satellite and Missile Observation System), originally named Sentry or Program (or Project) 101, 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).

The Samos E-1 series carried the E-1 frame readout camera with 1.83 m focal length, 30 m ground resolution, and 161 km × 161 km frame coverage. The Agena stage remained connected to the spacecraft and provided attitude control.

E-1 was mainly a component test payload. It carried also a cosmic ray detector, electric field plasma probe and acoustic and grid micrometeor detectors.

Samos 1, was launched on 11 October 1960. The satellite was destroyed after a second stage Agena failure. The first successful satellite in the series, Samos 2, was launched 31 January, 1961. Beginning with the launch of the second satellite, Samos was highly classified.

The Samos E-1 satellites included Samos F-1 ELINT package, which was housed in front of the optics. It was to be tested with calibration signals early in the mission and then to be ejected to allow the optical E-1 payload to work.

The third flight would have used an Agena-B upper stage. It was cancelled, but the Agena-B and the F-1 payload were converted to the P-102 Group 0-D mission.

Nation: USA
Type / Application: Reconnaissance, photo (film scan type)
Operator: US Air Force (USAF)
Equipment: E-1 camera, F-1 ELINT package
Configuration: Agena-A
Propulsion: Bell 8048
Power: Batteries
Lifetime: 10 days
Orbit: 557 km × 474 km, 97.4
Satellite COSPAR Date LS Launch Vehicle Remarks
Samos-E1 1 (Samos 1) 1960-F13 11.10.1960 Va LC-1-1 F Atlas-LV3 Agena-A with Samos F-1 #1
Samos-E1 2 (Samos 2) 1961 α 1 31.01.1961 Va LC-1-1 Atlas-LV3 Agena-A with Samos F-1 #2
Samos-E1 3 - not launched Va Atlas-LV3 Agena-B with Samos F-1 #3
Further Samos missions:

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