Explorer 12
First S-3 series satellite studying solar wind and cosmic rays.
Explorer 12, also known as EPE-A, Energetic Particles Explorer-A, and S3, was a NASA spacecraft tasked with investigating the solar wind, cosmic rays, and Earth's magnetic field. It launched on August 16, 1961, as the first in the S-3 series, which later included Explorers 14, 15, and 26. A power failure ended its transmissions on December 6, 1961.
Quick Facts
- Names list
- EPE-A
- Energetic Particles Explorer-A
- Explorer XII
- NASA S-3
- Operator
- NASA
- Harvard designation
- 1961 Upsilon 1
- Satcat
- 00170
- Mission duration
- 365 days (planned); 112 days (achieved)
- Spacecraft
- Explorer XII
- Spacecraft bus
- S-3
- Manufacturer
- Goddard Space Flight Center
Facts from the source article.
Instruments
Explorer 12 was built to investigate space physics, so it carried instruments like a cosmic-ray detector, a particle trapper, and a magnetometer. Its ten particle detection systems measured protons and electrons and how they relate to magnetic fields. A 16-channel time-division multiplexed telemeter sampled all channels every 0.324 seconds; half transmitted eight-level digital data, the other half analog. One analog channel, subcommutated over 16 frames, relayed spacecraft temperatures and power system voltages and currents. A digital solar aspect sensor measured spin period and phase to 0.041 seconds and the spin axis angle relative to the Sun within about 3 degrees.
Experiments
The experiment measured flux and energy spectra of charged particles and cosmic rays, using a shielded Anton type 302 omnidirectional Geiger–Müller tube detecting protons above 23 MeV and electrons above 1.6 MeV, an electron magnetic spectrometer with three thin-windowed Anton type 213 directional Geiger–Müller tubes sensitive to electrons from 40 to 100 keV, and three directional cadmium sulfide crystals for total flux of protons from 1 keV to 10 MeV and electrons from 200 eV to 500 keV. Counts accumulated for 10.24 seconds and were telemetered every 79 seconds. The Cosmic-Ray Experiment included a double scintillation counter measuring 55- to 500-MeV protons in six intervals and protons above 600 MeV, a single scintillator measuring 1.4- to 22-MeV protons at five thresholds and electrons above 150 keV, and a GM counter telescope for protons above 30 MeV, with a complete set every 6.8 minutes. An electrostatic analyzer with a current collector, designed to detect protons from 100 eV to 20 keV, apparently malfunctioned before injection into orbit and returned no useful data.
Mission
Explorer 12 functioned well after reaching orbit, with all instruments working normally. Its transmitter stopped on December 6, 1961, after relaying 2,568 hours of real-time data. Over its 112-day mission, it completed 102 orbits, gathering data about 80 percent of the time. The satellite yielded important geophysical findings on radiation and magnetic storms. It began spinning at 28.0 rpm, with its axis pointing at right ascension 48 degrees and declination -28 degrees; the spin gradually increased to 34.3 rpm.
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