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ORS Mk.3 (ERS)


From 1962 the US Air Force launched a series very small technology satellites called ERS (Environmental Research Satellites). The satellites were built by TRW Systems Group for the United States Air Force Office of Aerospace Research (AFOAR). Depending on the shape, these satellites are also referred to as the Tetrahedral Research Satellite (TRS) or Octahedral Research Satellite (ORS).

The basic configuration of the ORS Mk.3 spacecrafts was a regular octahedron measuring 28 cm on a side. Solar cells mounted on each side of the faces provide sufficient electrical power to operate the experiments and the telemetry system when the satellite is illuminated by the sun. No internal battery or command system were provided. The satellite subsystems consisted of electrical power, antenna, telemetry, experiments, and mechanical structure.


  • ORS 3 (ERS 17): Trapped radiation measurements for correlation with Vela data, Cosmic rays, Solar and galactic gamma and X-rays, 5.4 kg, operated for 104 days
  • ORS 4 (ERS 18): investigation of the Van Allen belts; carried six Geiger-Müller counters, low- and high-energy photomultiplier detectors, an X-ray detector, a solid state electron and proton detector and a surface barrier proton detector


  • ORS 3: 153 km × 112964 km × 34.4°
  • ORS 4: 8604 km × 111229 km × 32.8°
Nation: USA
Type / Application: Experimental
Operator: US Air Force (USAF)
Contractors: TRW Systems Group
Equipment: various: see above
Configuration: Octahedron (ORS Mk.3)
Propulsion: None
Power: Solar cells
Orbit: 566 km × 111790 km, 36.88° (#3); 8989 km × 110838 km, 33.31° (#4)
Satellite COSPAR Date LS Launch Vehicle Remarks
ORS 3 (ERS 17) 1965-058C 20.07.1965 CC LC-13 Atlas-LV3 Agena-D with Vela 5, Vela 6
ORS 4 (ERS 18) 1967-040C 28.04.1967 CC LC-41 Titan-3C with Vela 7, Vela 8, OV5 1, OV5 3


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