Depiction of Explorer 27 in orbit
|Mission duration||~8 Years|
|Start of mission|
|Launch date||29 April 1965|
|Launch site||Wallops Flight Facility|
|End of mission|
|Last contact||20 July 1973|
|Perigee altitude||932.3 km (579.3 mi)|
|Apogee altitude||1,311.3 km (814.8 mi)|
|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. 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. 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.
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. The passive laser reflectors continue to be used due to the low inclination.