The ISEE-2 (International Sun-Earth Explorer-B or ISEE-B) was an Explorer-class daughter spacecraft, International Sun-Earth Explorer-2, was part of the mother/daughter/heliocentric mission (ISEE-1, ISEE-2, ISEE-3). ISEE-2 was a 165.78 kg (365.5 lb) space probe used to study magnetic fields near the Earth. ISEE-2 was a spin-stabilized spacecraft and based on the design of the prior IMP (Interplanetary Monitoring Platform) series of spacecraft. ISEE-1 and ISEE-2 were launched on 22 October 1977, and they re-entered on 26 September 1987.

The program was a cooperative mission between NASA and ESRO (later European Space Agency (ESA)), a memorandum of understanding (MOU) between NASA and the European Space Agency, was signed in March 1975. The program was designed to study the interaction between the Earth's magnetic field and the solar wind. At least 32 institutions were involved, and the focus was on understanding magnetic fields. ISEE-1 and ISEE-3 were built by NASA, while ISEE-2 was built by ESA. All three had complementary instruments supported by the same group of over 100 scientists.

The purposes of the mission were: (1) to investigate solar-terrestrial relationships at the outermost boundaries of the Earth's magnetosphere, (2) to examine in detail the structure of the solar wind near the Earth and the shock wave that forms the interface between the solar wind and the Earth's magnetosphere, (3) to investigate motions of and mechanisms operating in the plasma sheets, and (4) to continue the investigation of cosmic rays and solar flare effects in the interplanetary region near 1 AU. The three spacecraft carried a number of complementary instruments for making measurements of plasmas, energetic particles, waves, and fields. The mission thus extended the investigations of previous IMP spacecraft. The mother/daughter portion of the mission consisted of two spacecraft (ISEE-1 and ISEE-2) with station-keeping capability in the same highly eccentric geocentric orbit with an apogee of 23 Earth radii (R_e). During the course of the mission, the ISEE-1 and ISEE-2 orbit parameters underwent short-term and long-term variations due to solar and lunar perturbations. These two spacecraft maintained a small separation distance, and made simultaneous coordinated measurements to permit separation of spatial from temporal irregularities in the near-Earth solar wind, the bow shock, and inside the magnetosphere. By maneuvering ISEE-2, the inter-spacecraft separation as measured near the Earth's bow shock was allowed to vary between 10 km (6.2 mi) and 5,000 km (3,100 mi); its value is accurately known as a function of time and orbital position.

ISEE-2 was a cylinder at 16 sided of 1.27 m (4 ft 2 in) of diameter and of 1.14 m (3 ft 9 in) in height. ISEE-2 had a thruster to adjust the spacing between the two spacecraft, depending on desired goal. Early results from duo stated that by having two spacecraft, the "spatial and temporal variations in the magnetosphere and solar wind" could be detected.

The spacecraft were spin stabilized, with the spin vectors maintained nominally within 1° of perpendicular to the ecliptic plane, pointing north. The spin rates were nominally 19.75 rpm for ISEE-1 and 19.8 rpm for ISEE-2, so that there was a slow differential rotation between the two spacecraft. The ISEE-2 body-mounted solar array supplied approximately 112 watts at launch. The ISEE-2 data rate was 2048 bit/s most of the time and 8192 bit/s during one orbit out of every five (with some exceptions).

This experiment was designed to determine, by using identical instrumentation on the mother/daughter spacecraft, the spatial extent, propagation velocity, and temporal behavior of a wide variety of particle phenomena. Electrons were measured at 2 and 6 keV and in two bands: 8 to 200 keV and 30 to 200 keV. Protons were measured at 2 and 6 KeV and in three bands: 8 to 200 keV, 30 to 200 keV, and 200 to 380 keV. The 30 keV threshold could be commanded to 15 or 60 keV. Identical instrumentation on each spacecraft consisted of a pair of surface-barrier, semiconductor detector telescopes (one with a foil and one without a foil) and four fixed-voltage electrostatic analyzers (two for electrons and two for protons). Channel multipliers were used as detectors with the fixed-voltage analyzers. The telescopes had a viewing cone with a 40° half-angle, oriented at about 20° to the spin axis.

This experiment was designed to study plasma velocity distributions and their spatial and temporal variations in the solar wind, bow shock, magnetosheath, magnetopause, and magnetotail (within the magnetosphere). One-, two-, and three-dimensional velocity distributions for positive ions and electrons were measured using two 90° spherical electrostatic analyzers with channeltron electron multipliers as detectors. In conjunction with similar instrumentation (1977-102A-01) for the mother spacecraft, protons from 50 eV to 40 keV (and electrons from 5 eV to 20 keV) were measured with 10% energy resolution in two ranges each.

This experiment was designed to study, by means of identical instrumentation on the mother/daughter spacecraft, the spatial and temporal variations of the solar wind and magnetosheath electrons and ions. Protons and electrons in the energy range from 1 eV to 45 keV were measured in 64 contiguous energy bands with an energy resolution (delta E/E) of 0.16. A quadrispherical low-energy proton and electron differential energy analyzer (LEPEDEA), employing seven continuous-channel electron multipliers in each of its two (one for protons and one for electrons) electrostatic analyzers was flown on both the mother and the daughter spacecraft. All but 2% of the 4 pi-sr solid angle was covered for particle-velocity vectors. A Geiger–Müller tube was also included, with a conical field of view of 40° full-angle, perpendicular to the spin axis. This detector was sensitive to electrons with E>45 keV, and to protons with E>600 keV.