Explorer 50, also known as IMP-J or IMP-8, was a NASAsatellite launched to study the magnetosphere. It was the eighth and last in a series of the Interplanetary Monitoring Platform.
Explorer 50 was a drum-shaped spacecraft, across and height, with propulsionStar-17A, instrumented for interplanetary and magnetotail studies of cosmic rays, energetic solar particles, plasma, and electric and magnetic fields. Its initial orbit was more elliptical than intended, with apogee and perigee distances of about 45 earth radii and 25 earth radii. Its eccentricity decreased after launch. Its orbital inclination varied between 0° and about 55° with a periodicity of several years. The spacecraft spin axis was normal to the ecliptic plane, and the spin rate was 22.3 rpm. The data telemetry rate was 1600 bps. The spacecraft was in the solar wind for 7 to 8 days of every 12 days orbit. Telemetry coverage was 90% in the early years, but only 60-70% through most of the 1980s and early 1990s. Coverage returned to the 90% range in the mid to late 1990s. The objectives of the extended Explorer 50 operations were to provide solar wind parameters as input for magnetospheric studies and as a 1 AU baseline for deep space studies, and to continue solar cycle variation studies with a single set of well-calibrated and understood instruments. In October, 2001, Explorer 50 was terminated as an independent mission. The last useful science data from Explorer 50 was acquired on 7 October 2006.
Instruments
MAG. This instrument studied of the interplanetary space, geomagnetic tail, and boundary magnetic fields. The resolution per sensor is ± 0.3 nT.
GAF. This instrument utilizes two wire antennas to measure DC electric fields in the solar wind and magnetosheath.
IOE. The instrument consists of a Low-Energy Proton and Electron Differential Energy Analyzer and a Geiger tube.
PLA. The objective is to study the positive ions and electrons in the solar wind, transition region, and magnetotail. Parameters derived on a routine basis are protonvelocity, number density, and temperature. ;Energetic particles
EPE. EPE is a solid-state telescope which measures fluxes of ions in four energy channels ranging from 0.05 MeV - 0.20 MeV to 2.1 MeV - 4.5 MeV, and electrons in the ranges 30-90 keV and 100-200 keV.
EECA. This instrument consists of 2 detector systems. An electrostatic deflectionspectrometer measures the energy per charge of incident ions in several ranges between 100 keV and 1000 keV.
CPME. The instrument is a solid-state telescope measuring fluxes of protons in 11 energy channels between 0.29 and 140 MeV, and alpha particles in 6 channels between 0.64 and 52 MeV/n. Time resolution for the measurement cycle is 10.24 seconds.
