Explorer 41
NASA satellite measuring particles and fields in cislunar space.
Explorer 41, also designated IMP-G and IMP-5, was a NASA satellite launched on 21 June 1969 as part of the Explorers program. It was the seventh satellite in the Interplanetary Monitoring Platform series, though it received the post-launch designation IMP-5 because two earlier flights had used the Anchored IMP designation. Its predecessor in the strict IMP series was Explorer 34, launched in May 1967.
Quick Facts
- Names list
- IMP-G
- IMP-5
- Interplanetary Monitoring Platform-5
- Operator
- NASA
- Satcat
- 03990
- Mission duration
- 3.5 years (achieved)
- Spacecraft
- Explorer XLI
- Spacecraft bus
- IMP
- Manufacturer
- Goddard Space Flight Center
- Launch mass
- 175 kg / 386 lb
Facts from the source article.
Spacecraft and mission
Explorer 41, also designated IMP-G, was a spin-stabilized spacecraft designed to study energetic particles, magnetic fields, and plasma in the region between Earth and the Moon. It operated in a highly elliptical orbit with a steep inclination. Its spin axis was oriented nearly perpendicular to the ecliptic plane, while the line connecting its closest and farthest orbital points was almost parallel to it. The satellite initially reached its farthest point from Earth around 1:00 PM local time, spinning at 27.5 rotations per minute. Telemetry data was transmitted in 20.48-second cycles. The spacecraft returned data almost continuously, except for a period between mid-November 1971 and early February 1972 when readings were only taken near the magnetotail's neutral sheet.
Experiments
One experiment used a parallel-plate electric-field analyzer and two funnel-shaped channel multipliers. The parallel-plate analyzer served as a discriminatory device. One channel multiplier responded to electrons with energies between 2.5 and 7.5 keV, the other to electrons between 7.5 and 12.5 keV. Their acceptance cones had full-angles of approximately 30° with axes of symmetry 60° off the spacecraft spin axis. Only low-quality data were obtained due to high background count rates. Another experiment studied solar particle anisotropy and its variation with time. A telescope of three aligned detectors (A solid-state, B plastic scintillator, C CsI scintillator) and a plastic anticoincidence shield (D) measured protons from 0.8 to 7.0 MeV (counts in A but not B) and from 35 to 110 MeV (coincident counts in B and C but not D). Pulse-height analysis gave six-point spectra within each interval. Protons from 7 to 55 MeV (counts in A and B) were recorded without spectral information. A proportional counter provided directional measurements of X-rays above 2 keV and electrons above 70 keV. Counts in each particle mode were obtained in eight octants in the ecliptic plane; X-ray counts came from the solar octant. A complete set of count rates and spectral data was obtained every 81.9 seconds. A third experiment used a dE/dx versus E telescope with thin and thick CsI scintillators and an anticoincidence plastic scintillator. The telescope axis was parallel to the spacecraft spin axis. Counts of particles penetrating the thin CsI and stopping in the thick CsI were accumulated for two 4.48-second intervals each 2.73 minutes. The relative contribution of various species (electrons between 2.7 and 21.5 MeV, nuclei with charge 1 or 2, atomic mass 1, 2, 3 or 4, and energy between 18.7 and 81.6 MeV/nucleon) and energy spectral information were determined by 1024-channel pulse-height analysis performed simultaneously on both CsI outputs 16 times every 2.73 minutes. Counts of electrons between 0.3 and 0.9 MeV stopping in the thin scintillator were also obtained once each 2.73 minutes. This experiment functioned well.
More in NASA Space Probes
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced