Explorer 12 (EPE A) [NASA]

EPE (Energetic Particles Explorer) were a series ofspin-stabilized, solar-cell-powered spacecraft instrumented to measure cosmic-rayparticles, trapped particles, solar wind protons, and magnetospheric and interplanetarymagnetic fields.

Explorer 12 was instrumented to measure cosmic-ray particles, trappedparticles, solar wind protons, and magnetospheric and interplanetary magnetic fields. Itwas the first of the S 3 series of spacecraft. A 16-channel PFM/PM time-divisionmultiplexed telemeter was used. The time required to sample the 16 channels (one frameperiod) was 0.324 s. Half of the channels were used to convey eight-level digitalinformation, and the other channels were used for analog information. During groundprocessing of the telemetered data, the analog information was digitized with an accuracyof 1/100th of full scale. One analog channel was subcommutated in a 16-frame-long patternand was used to telemeter spacecraft temperatures, power system voltages, currents, etc. Adigital solar aspect sensor measured the spin period and phase, digitized to 0.041 s, andthe angle between the spin axis and sun direction to about 3-deg intervals. The spacecraftfunctioned well until 6 December 1961, when it ceased transmitting data apparently as aresult of failures in the power system. Good data were recorded for approximately 90% ofthe active lifetime of the spacecraft. The initial spin rate was 28.0 rpm, and the spinaxis direction was right ascension 48 deg, declination -28 deg. The direction was nearlyconstant with time, and the spin rate slowly increased with time to 34.3 rpm. Apogeedirection varied from about 1200 h to 0600 h local time.

• Electrostatic Analyzer of Solar Plasma
• Fluxgate Magnetometers
• Charged Particles
• Solar Cell Damage Experiment
• Proton-Electron Scintillation Detector
• Cosmic Rays

Explorer 14 was instrumented to measure cosmic-ray particles,trapped particles, solar wind protons, and magnetospheric and interplanetary magneticfields. It was the second of the S 3. A 16-channel PFM/PM time-division multiplexedtelemeter was used. The time required to sample the 16 channels (one frame period) was0.323 s. Half of the channels were used to convey eight-level digital information, and theothers were used for analog information. During ground processing of the telemetered data,the analog information was digitized with an accuracy of 1/100th of full scale. One analogchannel was subcommutated in a 16-frame-long pattern and was used to telemeter spacecrafttemperatures, power system voltages, currents, etc. A digital solar aspect sensor measuredthe spin period and phase, digitized to 0.041 s, and the angle between the spin axis andsun direction to about 3-deg intervals. The spacecraft functioned well except for theperiod from January 10 to 24, 1963, and after 11 August 1963, when the encodermalfunctioned terminating the transmission of usable data. Good data were recorded forapproximately 85% of the active lifetime of the spacecraft. The spacecraft was coning(37-deg maximum half-angle) until 10 January 1963. After 24 January 1963, it wasspin-stabilized at a rate of 10 rpm. This rate slowly decreased to 1 rpm on 8 July 1963.Initially, the local time of apogee was 0700 h.

• Proton Analyzer
• Fluxgate Magnetometers
• Trapped Particle Radiation
• Cosmic Rays
• Solar Aspect Sensor
• Electrolytic Timer Experiment
• Solar Cell Damage Experiment
• Proton-Electron Scintillation Detector

Explorer 15 was instrumented to study the artificial radiation beltproduced by the Starfish high-altitude nuclear burst of July 1962. The backup payload forExplorer 14 was modified and used for Explorer 15. The instrumentation included three setsof particle detectors to study both electrons and protons, and a two-axis fluxgatemagnetometer to determine magnetic aspect. A 16-channel PFM/PM time-division multiplexedtelemeter was used. The time required to sample the 16 channels (one frame period) was0.323 s. Half of the channels were used to convey eight-level digital information, and theothers were used for analog information. During ground processing of the telemetered data,the analog information was digitized with an accuracy of 1/100th of full scale. One analogchannel was subcommutated in a pattern 16 frames long and was used to telemeter spacecrafttemperatures, power system voltages, currents, etc. A digital solar aspect sensor measuredthe spin period and phase, digitized to 0.041 s, and the angle between the spin axis andthe sun direction to about 3-deg intervals. During launch the spacecraft failed to despin.The spin rate ranged from 72.9 to 73.2 rpm during the life of the spacecraft. The spinaxis pointed at right ascension 80.97 deg and declination 20.9 deg.

• Electron and Proton Solid-State Detectors
• Angular Distribution
• Proton-Electron Scintillation Detector
• Fluxgate Magnetometers
• Directional and Omnidirectional Energetic Protons and Electrons

Explorer 26 was instrumented to measure trapped particles and thegeomagnetic field. A 16-channel PFM/PM time-division multiplexed telemeter was used. Thetime required to sample the 16 channels (one frame period) was 0.29 s. Half of thechannels were used to convey eight-level digital information. The other channels were usedfor analog information. During ground processing, the analog information was digitizedwith an accuracy of 1/800th of full scale. One analog channel was subcommutated in a16-frame-long pattern and used to telemeter spacecraft temperatures, power systemvoltages, currents, etc. A digital solar aspect sensor measured the spin period and phase,digitized to 0.036 s, and the angle between the spin axis and sun direction to about 3-degintervals. The spacecraft systems functioned well, except for some undervoltage turnoffs,until 26 May 1967, when the telemeter failed. The initial spin rate was 33 rpm, and thespin axis direction was right ascension 272.8 deg and declination 21.5 deg. The spin ratedecreased with time to 2 rpm on 9 September 1965. For the balance of its life, thespacecraft was coning or tumbling at a rate of about 1 rpm.

• Solid-State Electron Detector
• Omnidirectional and Unidirectional Electron and Proton Fluxes
• Fluxgate Magnetometers
• Proton-Electron Scintillation Detector
• Solar Cell Damage

A back-up satellite of the Explorer-12 is on display in the Space Science exhibition station at the Steven F. Udvar-Hazy Center in Chantilly, VA.

References:

• NSSDC Master Catalog:Explorer-12
• NSSDC Master Catalog:Explorer-14
• NSSDC Master Catalog:Explorer-15
• NSSDC Master Catalog:Explorer-26

• Explorer Program

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