Explorer 41, also called IMP-G and IMP-5, was a NASA satellite launched as part of the Explorers program. Explorer 41 launched on 21 June 1969 from Vandenberg AFB, California, with a Thor-Delta E1 launch vehicle. Explorer 41 was the seventh satellite launched as part of the overall Interplanetary Monitoring Platform series, though it received the post-launch designation "IMP-5" because two previous flights had used the "AIMP" ("Anchored IMP") designation instead. It was preceded by the second of those flights, Explorer 35 ([A]IMP-E / AIMP-2), launched in July 1967. Its predecessor in the strict IMP series of launches was Explorer 34, launched in May 1967, which shared a similar design to Explorer 41. The next launch of an IMP satellite was Explorer 43 (IMP-I / IMP-6) in 1971.

Explorer 41 (IMP-G) was a spin-stabilized satellite placed into a high-inclination, highly elliptical orbit to measure energetic particles, magnetic fields, and plasma in cislunar space. The line of apsides and the satellite spin vector were within a few degrees of being parallel and normal, respectively, to the ecliptic plane. Initial local time of apogee was about 13:00 hours. Initial satellite spin rate was 27.5 rpm. The basic telemetry sequence was 20.48-seconds. Data transmission was nearly 100% for the spacecraft life except for the interval from 15 November 1971 to 1 February 1972, when data acquisition was limited to the vicinity of the magnetotail neutral sheet.

The instrumentation for this experiment consisted of a parallel-plate electric-field analyzer and two funnel-shaped channel multipliers. The parallel-plate analyzer was used as a discriminatory device. One of the channel multipliers responded to electrons with energies between 2.5 and 7.5-keV, and the other responded to electrons with energies between 7.5 and 12.5-keV. The acceptance cones for the channel multipliers had full-angles of approximately 30° with axes of symmetry 60° off the spacecraft spin axis. Due to high background count rates, only data of low quality were obtained.

This experiment was designed to study solar particle anisotropy and its variation with time. A telescope, consisting of three aligned detectors (A-solid state, B-plastic scintillator, C-Caesium iodide (CsI) scintillator) and a plastic scintillator anticoincidence shield (D), was used to measure protons from 0.8 to 7.0-MeV (counts in A but not in B) and from 35 to 110-MeV (coincident counts in B (dE/dx) and C (total E) but not in D). Pulse-height analysis yielded six-point spectra within each of these two energy intervals. Protons from 7 to 55-MeV (counts in A and B) were also recorded without spectral information. In addition, a proportional counter provided directional measurements of X-rays with energies above 2-keV and electrons above 70-keV. Counts in each particle counting mode were obtained in each of eight octants in the ecliptic plane. X-ray counts were obtained in the solar octant. A complete set of count rates and spectral data was obtained every 81.9-seconds.

This experiment used a dE/dx versus E telescope with thin and thick CsI scintillators (one each) and an anticoincidence plastic scintillation counter. The telescope axis was parallel to the spacecraft spin axis. Counts of particles penetrating the thin CsI scintillator and stopping in the thick CsI scintillator were accumulated for two 4.48-seconds intervals each 2.73-minutes. The relative contribution to the count rate 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 the output of both CsI scintillators 16 times every 2.73-minutes. In addition, counts of electrons between 0.3 and 0.9-MeV stopping in the thin scintillator were also obtained once each 2.73-minutes. The experiment functioned well.

This experiment was designed to measure separately the contributions of solar nuclei and galactic nuclei (Z<14) using a combination solid-state and Cherenkov counter cosmic ray telescope. The detector was designed for energy loss vs range or total energy measurements for protons (differential measurements between 0.8 and 119-MeV and an integral measurement between 119-MeV and 1-GeV). Similar differential energy measurements of He and higher Z nuclei were made between 3 MeV/nucleon and 1 GeV/nucleon. The detector was oriented perpendicular to the satellite spin axis. The detector accumulators were telemetered four times every 20.48-seconds. Each accumulation was 4.8-seconds long (spacecraft initial spin period was about 2.2-seconds). The output from the three 256-channel pulse-height analyzers was obtained every 5.12-seconds and was telemetered along with the detector accumulators. The D3 element of the telescope became noisy on 29 September 1969, and the condition continued until the spacecraft emerged from first shadow on 5 January 1970. Otherwise the experiment performed normally until the spacecraft decayed from orbit on 23 December 1972.

An electrostatic analyzer and an E-cross-B velocity selector normal to the spacecraft spin axis were used to separately determine proton and alpha particle spectra in the solar wind. For each species, measurements in the energy per charge range 310 to 5100-eV were made at 14 points logarithmically equispaced in energy. During individual spacecraft rotations, counts were obtained in each of sixteen 22.5-deg sectors for a given species and energy. The sum of these counts, the sum of the squares of these counts, and the sector number of maximum counting were telemetered to Earth. After successive 61.44-seconds spectral determinations for protons and alpha particles, 15 consecutive readings for protons at 1408 eV were obtained. A period of 3.07-minutes separated two spectra of the same species. The instrument operated intermittently.

This experiment was designed to measure energetic charged particle populations in and beyond the Earth's outer magnetosphere and the dynamic processes that influence these populations. The instrumentation consisted of a 10 cm (3.9 in)-diameter Neher-type integrating ionization chamber and three pairs of Geiger–Müller tubes (GM). The ionization chamber responded omnidirectionally to electrons above 700-keV, protons above 12-MeV, and X-rays above 20-keV. Each pair of GM tubes had one member normal to, and the other parallel to, the spacecraft spin axis. All but one tube had 70° full-width acceptance cones. The members of one pair of GM tubes responded to electrons above 80-keV and protons above 1.5-MeV. The second pair of GM tubes responded to electrons above 45-keV scattered from gold foils. The third tube, normal to the spin axis, responded to electrons above 120-keV, protons above 2.3-MeV, and X-rays from 3 to 20-keV (0.1% efficiency). The other member of the third set of GM tubes responded to electrons above 18 keV and protons above 250 keV. Pulses from the ionization chamber and counts from each of the GM tubes were accumulated for 9.92-seconds and read out four times each 40.96-seconds. The experiment performed normally from launch until the spacecraft decayed from orbit on 23 December 1972, except that the ionization chamber operated intermittently throughout the mission.