Explorer 47 (IMP-H or IMP-7), was a NASA satellite launched as part of the Explorers program. Explorer 47 was launched on 23 September 1972 from Cape Canaveral, Florida, with a Thor-Delta 1604. Explorer 47 was the ninth overall launch of the Interplanetary Monitoring Platform series, but received the launch designation "IMP-7" because two previous "Anchored IMP" flights had used "AIMP" instead.

Explorer 47 continued the study begun by earlier IMP spacecraft of the interplanetary space and magnetotail regions from a nearly circular orbit, near 37 Earth radii. This 16 sided drum-shaped spacecraft was 157 cm (62 in) in height and 135 cm (53 in) in diameter, with propulsion Star-17A.

Explorer 47 was designed to measure energetic particles, plasma, electric fields and magnetic fields. The spin axis was normal to the ecliptic plane, and the spin period was 1.3 seconds. The spacecraft was powered by solar cells and a chemical battery. Scientific data were telemetered at 1600 bit/s (with a secondary 400 bit/s rate available).

Explorer 47 was launched on 23 September 1972, at 01:20:00 UTC, from Cape Canaveral, Florida, with a Thor-Delta 1604 launch vehicle.

Three solid-state detectors in an anticoincidence plastic scintillator observed electrons between 0.2 and 2.5-MeV, protons between 0.3 and 500-MeV, alpha particles between 2.0 and 200-MeV, heavy particles with atomic numbers ranging from 2 to 5 with energies greater than 8-MeV, heavy particles with Z values ranging between 6 and 8 with energies greater than 32-MeV, and integral protons and alpha of energies greater than 50-MeV/nucleon, all with dynamic ranges of 1 to 1E+6 particles per (cm² s sr). Five thin-window Geiger–Müller tubes observed electrons of energy greater than 15-keV, protons of energy greater than 250-keV, and X-rays with wavelengths between 2 and 10 A, all with a dynamic range of 10 to 1E+8 particles per (cm² s sr). Particles and X-rays (primarily of solar origin) were studied, but the dynamic range and resolution of the instrument permitted cosmic rays and magnetotail particles to be observed.

This experiment was designed to measure solar and galactic electrons, positrons, and nuclei, and to separate isotopes from hydrogen through oxygen. The energy ranges covered were 0.16 to 5-MeV (electrons), 0.16 to 2-MeV (positrons), and about 1 to 40-MeV/nucleon for nuclei. The instrument was a telescope consisting of 11 colinear, fully depleted, silicon surface-barrier detectors inside a plastic scintillator anticoincidence shield. Four of the top five sensors were annular while the remainder were solid disks. This arrangement gave narrow geometry (anticoincidence in annular sensors) and wide geometry modes with half-angle acceptance cones of about 24° and 36°. The telescope axis was perpendicular to the spacecraft spin axis. Data returned consisted of 8-sectored and spin-integrated count rates for 8 different coincidence/anticoincidence modes and 2 parameter pulse-height analyses for 32 particles every 20.48-seconds. The coincidence mode chosen for pulse-height analysis in any 0.64-seconds interval was fixed by a five-level priority system. The principal contributors to each coincidence mode rate were: (1) 0.16- to 5-MeV electrons and 1- to 43-MeV/nucleon nuclei, (2) 1- to 5-MeV electrons and 13- to 43-MeV/nucleon nuclei, (3) neutrals and gamma rays, (4) 0.2- to 1-MeV electrons, (5) 1- to 3-MeV electrons, (6) 1.2- to 2.4-MeV/nucleon nuclei, (7) 4- to 13-MeV/nucleon nuclei and (8) electrons above 3-MeV and nuclei above 30-MeV/nucleon.

The purposes of this investigation were: (1) to study the propagation characteristics of solar cosmic rays through the interplanetary medium over the energy ranges indicated below, (2) to study electron and proton fluxes throughout the geomagnetic tail and near the flanks of the magnetosphere, and (3) to study the entry of solar cosmic rays into the magnetosphere. The instrumentation consisted of a three-element telescope employing fully depleted surface-barrier solid-state detectors and a magnet to deflect electrons. Two sidemounted detectors were used to measure the deflected electrons. The experiment was designed to measure: (1) proton fluxes from 30-keV to >8.6-MeV in six ranges; (2) electron fluxes from 30-keV to >450-keV in three ranges; (3) charged particles with E>15-keV; (4) alpha particles >0.5-MeV, >1.6-MeV, 2.2 to 8.8-MeV and 8.8 to 35-MeV; and (5) charged particles of Z>2 and E>5-MeV.

This experiment was designed to determine the composition and energy spectra of low-energy particles associated with solar activity and interplanetary processes. The detectors used were: (1) an electrostatic analyzer (to select particles of the designated energy per charge) combined with an array of windowless solid-state detectors (to measure the energy loss) and surrounded by an anticoincidence shielding, and (2) a particle telescope consisting of a silicon surface-barrier detector and a flat two-chamber proportional counter enclosed in an anticoincidence scintillator cup. The experiment measured particle energies from 0.1 to 2 MeV per charge in 12 bands and uniquely identified positrons and electrons as well as nuclei with charges of Z from 1 to 8 (and charge group resolution for Z between 9 and 28). Two 1000-channel pulse-height analyzers, one for each element of the telescope, were included in the experiment payload. The telescope failed on 25 November 1972, when the window on the proportional counter weakened and burst due to exposure to UV radiation.