The Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX or Explorer 68) was a NASA solar and magnetospheric observatory and was the first spacecraft in the Small Explorer program. It was launched into low Earth orbit on 3 July 1992 from Vandenberg Air Force Base (Western Test Range) aboard a Scout G-1 launch vehicle. SAMPEX was an international collaboration between NASA and the Max Planck Institute for Extraterrestrial Physics of Germany (which provided the Heavy Ion Large Telescope). The Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX) is the first of a series of spacecraft that was launched under the Small Explorer (SMEX) program for low-cost spacecraft.
Mission The main objectives of SAMPEX experiments were to obtain data for several continuous years on the anomalous components of cosmic rays, on solar energetic particle emission from the Sun, and on the precipitating magnetospheric relativistic electrons. The orbit of SAMPEX has an altitude of 520 × 670 km (320 × 420 mi) and an 82 deg inclination. The spacecraft uses an onboard 3-axis stabilized solar-pointed/momentum bias system with the pitch axis pointed toward the Sun. Solar panels provide power for operations, including 16.7 watts for science instruments. An on-board Data processing unit (DPU) preprocesses the science and other data and stores them in a Recorder/Processor/Packetizer (RPP) unit of about 65 Mb, before transmitting in the S-band at a rate of 1.5 Mbit/s over Wallops Flight Facility (WFF) (or a back-up) station. The command memory can store at least a thousand commands. The science instruments generally point toward local zenith, especially over the terrestrial poles, for optimal sampling of galactic and solar cosmic ray flux. Energetic magnetospheric particle precipitation is monitored at lower geomagnetic latitudes.
Spacecraft
It carries four science instruments: (1) low-energy ion composition analyzer (LICA); (2) heavy ion large telescope (HILT); (3) mass spectrometer telescope (MAST); and (4) proton-electron telescope (PET). Estimated useful lifetime of the spacecraft was about three years; however, the data stream continued to 30 June 2004. In 1997, NASA Goddard transferred operation of SAMPEX to the Flight Dynamics and Control Laboratory (FDCL) housed within the Aerospace Engineering Department of the University of Maryland, College Park.
Instruments The spacecraft carried four instruments designed to measure the anomalous components of cosmic rays, emissions from solar energetic particles, and electron counts in Earth's magnetosphere. Built for a three-year mission, its science mission was ended on 30 June 2004. Mission control for SAMPEX was handled by the Goddard Space Flight Center until October 1997, after which it was turned over to the Bowie State University Satellite Operations Control Center (BSOCC). BSOCC, with funding assistance from The Aerospace Corporation, continued to operate the spacecraft after its science mission ended, using the spacecraft as an educational tool for its students while continuing to release science data to the public.
Experiments
Heavy Ion Large Telescope (HILT) The HILT experiment was designed to measure the charge, energy, and mass of cosmic rays in the energy range of about 8.0-310 MeV/nucleon. Specifically, the energy ranges were: Helium (He): 3.9 - 90 MeV/nucleon; Carbon (C): 7.2 - 160 MeV/nucleon; Oxygen (O): 8.3-310 MeV/nucleon; Neon (Ne): 9.1-250 MeV/nucleon; and, Iron (Fe): 11-90 MeV/nucleon. The instrument consisted of (a) an array of position-sensitive proportional counters at the entrance, followed by (b) an ionization chamber, (c) another array of position-sensitive proportional counters just before, (d) a coplanar, 10-element, solid state array of detectors. The detectors were backed by (e) a large caesium iodide (CsI) scintillation counter which was viewed by four light-sensitive diodes. The geometric factor was as large as 35 cm2-sr. The two position-sensitive counters enabled computation of the exact length of the trajectory along the ionization chamber. Items (a), (b), and (c) were filled with flowing isobutane gas at a pressure of 75 Torr. The 8.5 kg (19 lb) of liquid isobutane was sufficient for a three-year operation. The instrument was basically a dE/dx versus E system; dE/dx was provided by (a), (b), and (c), and E was provided by (d) and (e). The telemetered signals from all the sensors enabled accurate determination of isotopic mass, charge and energy. However, isotopic resolution was poor at the high-energy end of each band, especially for the heavier elements. Species-dependent fluxes were, however, readily computed even at the high energy ends.
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