Explorer 26
Explorer 26 was a NASA satellite launched on 21 December 1964, as part of NASA's Explorer program. Its primary mission was to study the Earth's magnetic field. Spacecraft Explorer 26 was a spin-stabilized, solar-cell-powered spacecraft instrumented to measure trapped particles and the geomagnetic field and weighing . Experiments It carried five experiments: Solid-State Electron Detector, Omnidirectional and Unidirectional Electron and Proton Fluxes, Fluxgate Magnetometers, Proton-Electron Scintillation Detector, and Solar Cell Damage. The Solar Cell Damage experiment was intended to quantify the degradation of solar cell performance due to radiation, and evaluate the effectiveness of glass shields at preventing this degradation. A 16-channel PFM/PM time-division multiplexed telemeter was used. The time required to sample the 16 channels (one frame period) was 0.29 seconds. Half of the channels were used to convey eight-level digital information. The other channels were used for analog information. During ground processing, the analog information was digitized with an accuracy of 1/800th of full scale. One analog channel was subcommutated in a 16-frame-long pattern and used to telemeter spacecraft temperatures, power system voltages, currents, etc. A digital solar aspect sensor measured the spin period and phase, digitized to 0.036 seconds, and the angle between the spin axis and Sun direction to about 3° intervals. Fluxgate Magnetometers The purpose of this experiment was to measure the magnitude and direction of the Earth's magnetic field over the spacecraft orbit. Three orthogonal components were measured by a boom-mounted biaxial magnetometer during each spacecraft revolution. Each axis had a range of plus and minus 2000 nT and an accuracy of 5 nT. The sampling rate was 3.13 Hz. The experiment provided useful data from launch until 30 June 1965, after which spacecraft tumble rendered field direction determination impractical. Omnidirectional and Unidirectional Electron and Proton Fluxes Omnidirectional fluxes of 40- to 110-MeV protons and of electrons greater than about 4 MeV were separably measured by a plastic scintillator. A second plastic scintillator with an 8° half-angle aperture and a look direction perpendicular to the spacecraft spin axis separably measured protons above 5.2 MeV and electrons above 0.5 MeV. The ability to distinguish between the particle types was due to the presence of two discrimination levels associated with each detector. High-quality data transmission from this experiment was essentially continuous from launch until about the middle of 1966, and then intermittent. Proton-Electron Scintillation Detector This experiment was designed to measure the directional fluxes and spectra of low-energy trapped and auroral protons and electrons. It employed a 5-mg-thick powder phosphor scintillator with a 1000-A aluminum coating. Additional absorbers were inserted in the detector aperture by a 16-position stepped wheel. The aperture was pointed at 45° to the spin axis. Due to the thinness and type of phosphor, the detector in the pulse mode would respond only to low-energy ions, and, therefore, essentially measured the flux of protons that penetrated the absorbers and stopped in the phosphor. Both the pulse counting rate and the phototube current were telemetered once each frame period. Sixteen readings were telemetered in