Explorer 27

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Explorer 27
Depiction of Explorer 27 in orbit
COSPAR ID1965-032A
SATCAT no.01328Edit this on Wikidata
Mission duration~8 Years
Spacecraft properties
PowerSolar Panels
Start of mission
Launch date29 April 1965 (1965-04-29)
Launch siteWallops Flight Facility
End of mission
Last contact20 July 1973 (1973-07-21)
Orbital parameters
Reference systemGeocentric
Perigee altitude932.3 km (579.3 mi)
Apogee altitude1,311.3 km (814.8 mi)
Period107.6 minutes
Radio Beacon, Langmuir probe

Explorer 27 (or BE-C or Beacon Explorer-C or Beacon-C) was a satellite, launched in 1965, designed to conduct scientific research in the ionosphere.[1] It was powered by 4 solar panels. One goal or the mission was to study in detail the shape of the Earth by way of investigating variations in its gravitational field.[2] It was the third and last of the Beacons in the Explorers program. The satellite was shut off in 1973 because its transmission band was going to be used by higher-priority spacecraft.


Explorer 27 carried four instruments, located on the main bus. They included a Langmuir probe, used to measure the temperature or the surrounding space, a Radio Beacon to test new means of ground-to-space communication, a Doppler navigation experiment, a passive laser reflector to allow tracking. A three-axis magnetometer measured the orientation compared to the local magnetic field due to the Earth, and there was also a Sun sensor. A bar magnet and damping rod caused the satellite spin to match up with the magnetic field direction.[1]

The radio transmitter operated on 162 and 324 MHz. However it was turned off on 20 July 1973 because it was interfering with other satellites.[1] The passive laser reflectors continue to be used due to the low inclination.[3]


  1. ^ a b c "NASA - NSSDCA - Spacecraft - Details". nssdc.gsfc.nasa.gov.
  2. ^ "Explorer Series of Spacecraft". NASA. Retrieved April 12, 2018.
  3. ^ "International Laser Ranging Service: Beacon-C". ilrs.cddis.eosdis.nasa.gov. Retrieved 2018-04-19.

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