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STEP 4 (P95-1)


STEP 4 (Space Test Experimental Program 4) was a technology demonstration satellite flown under the Space Test Program (STP).

It hosted three DoD payloads:

  • Digital Ion Drift Meter (DIDM) to study ion drift,
  • Electromagnetic Propagation Experiment (EMPE) to aid study radio propagation through the ionosphere, and
  • Orbiting Ozone and Aerosol Measurement (OOAM) to study ozone and water vapour in the middle atmosphere.

After reaching orbit, the solar panels failed to deploy properly, and there has been little or no uplink or downlink contact with the spacecraft. The mission was declared a failure soon after launch.

Nation: USA
Type / Application: Experimental
Operator: USAF STP (Space Test Program)
Contractors: TRW, CTA → Orbital Sciences Corporation (OSC) (Bus)
Equipment: DIDM, EMPE, OOAM
Configuration: LEOStar
Propulsion: ?
Power: 4 deployable fixed solar arrays, batteries
Mass: 403 kg
Orbit: 430 km × 500, 45, was to be m
Satellite COSPAR Date LS Launch Vehicle Remarks
STEP 4 (P95-1) 1997-063A 22.10.1997 WI, L-1011, RW04/22 Pegasus-XL


Further STP missions: