Langmuir Probes Two cylindrical electrostatic probes of the
Langmuir probe type were used. They consisted of a collector electrode extending from the central axis of a cylindrical guard ring. The guard ring extended from the spacecraft and the probe extended . A 2-
Hz sawtooth voltage of -3 to +5
volts was swept to either of the probes, and the resulting current profile to the probe was telemetered. From this profile, the
electron density,
electron temperature, and mean
ion mass were determined. This experiment performed nominally from launch until 13 August 1968, when solar cell degradation resulting from radiation prevented operation of all systems on the satellite. The probe was not operated after that time. No archival data were produced since the experiment was a back-up for the
Explorer 22 (BE-B) mission, which had been flown successfully.
Laser Tracking Reflectors The passive optical laser experiment, which consisted of nine panels on the spacecraft, was used to determine the spacecraft range and angle. Each panel was covered with 40
quartz cube-corner prisms that provided laser tracking capabilities for optical tracking studies. The ground-based optical transmitter was a pulsed 1-ms
ruby laser. A
photodetector determined whether the laser beam interrupted the spacecraft.
Radio Beacon A radio beacon radiated a plane-polarized signal at 20.005 MHz, 40.010 MHz, 41.010 MHz, and 360.090 MHz, all harmonics of 1.00025 MHz. The plane of polarization of the three lower frequencies underwent an appreciable number of rotations due to electron concentration. The polarization plane of highest frequency did not rotate appreciably. Several methods were used to analyze these rotations and determine the total electron content between the satellite and a ground receiver. The beacons were on until the satellite operation terminated on 6 May 1968. On 13 February 1970, the beacons were again turned on to replace the Explorer 22 (1964-064A - BE-B) beacons which had completely failed by the end of January 1970.
Radio Doppler System Two coherent, unmodulated CW transmitters, operating on frequencies of 162 and 324 MHz, allowed the Tranet Doppler Network to obtain data for studies of dynamic
geodesy. The frequencies were generated from redundant, dual, ultra-stable crystal oscillators operating on a frequency of 5 MHz minus 80 ppm. The system operated as planned. == Results ==