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Explorer S55



Explorer (S-55), also known as Meteoroid Sat A, was launched using a Scout 5 rocket from the Wallops Flight Facility. Its mission was to evaluate the launch vehicle, and investigate micrometeoroid impact and penetration. The mission failed because the third stage failed to ignite at about 110 km altitude, and the spacecraft did not achieve orbit, falling back into the Atlantic Ocean.

The S-55 satellite was the fourth Altair stage of the launch vehicle. It had a diameter of 61 cm (24 in.), a length of 193 cm (76 in.), and a mass of 85 kg (187 lbs.). Four whip antennas extended from the nose section, and two separate telemetry transmitters, at 136.86 and 136.20 MHz could be turned on for a minute at a time by ground command. At these times it would read out from a data storage unit. A beacon also operated continuously at 136.86 MHz, powered by mercury batteries. Power was supplied by solar cells mounted on the side of the nose section, charging nickel-cadmium batteries.

The payload consisted of six experiments. The first comprised 160 half-cylinder cells, pressurized with nitrogen and made of varying thickness of beryllium-copper. The second had 60 triangular foil gauge detectors mounted under stainless steel skins. The third had 46 copper wire grids wound on melamine cards. The fourth consisted of two cadmium-sulfide cells mounted in aluminized glass flasks. Piezoelectric crystal impact transducers made up the fifth experiment, and the sixth had five groups of p-on-n solar cells with various protective coverings.

Alternate Names

  • S 55
  • Meteoroid Satellite A
  • Micrometeorite Explorer
  • ExplorerS55

Facts in Brief

Launch Date: 1961-06-30
Launch Vehicle: Scout
Launch Site: Wallops Island, United States
Mass: 84.8 kg

Funding Agency

  • NASA-Office of Space Science Applications (United States)


  • Planetary Science

Additional Information

Questions and comments about this spacecraft can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail

Selected References

  • Micrometeoroid satellite S-55, NASA, N-90,006, Wash., D.C., June 1961.
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