The ISEE-1 (International Sun-Earth Explorer-A or ISEE-A) was an Explorer-class mother spacecraft, International Sun-Earth Explorer-1, was part of the mother/daughter/heliocentric mission (ISEE-1, ISEE-2, ISEE-3). ISEE-1 was a space probe used to study magnetic fields near the Earth. ISEE-1 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.
Mission
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 (Re). 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 and ; its value is accurately known as a function of time and orbital position.
The program was a cooperative mission between NASA and European Space Research Organisation (ESRO) (later European Space Agency (ESA)) 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.
Spacecraft ISEE-1 was a cylinder at 16 sided of of diameter and of in height. 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-1 body-mounted solar array provided approximately 175 watts initially and 131 watts after three years, at 28 volts during normal operation. The ISEE-1 data rate was 4096 bit/s most of the time and 16384 bit/s during one orbit out of every five (with some exceptions).
Experiments DC and low frequency electric fields, double-probe (0.19-1900 Hz) This experiment was intended to study quasi-static electric fields and low-frequency plasma waves in the plasmasphere, magnetosphere, magnetosheath, and solar wind. The double-probe floating-potential technique was applied using long-wire antenna probes with an effective electric field baseline of . The DC differential voltage was measured 8 or 32 times per second, depending on bit rate. In addition, the DC field was measured at selected azimuthal angles relative to the Sun and the magnetic field, and the peak value of delta-v and its azimuthal angles were measured. Low-frequency waves were measured in eight frequency bands as follows: 0.19 to 0.6, 0.6 to 1.9, 1.9 to 6, 6 to 19, 19 to 60, 60 to 190, 190 to 600, and 600 to 1900 Hz. The DC-mode measurements had a two-step, variable-gain amplifier controlled from the ground. The resolution in the highest gain state was 0.5E-6 V/m. The AC measurement electronics consisted of two amplifier sections. One amplifier was used for low-frequency channels, and one for high-frequency channels. Gain lines for each amplifier were independently controllable from the ground. In the highest-gain mode, each analyzer channel had a sensitivity of 0.04E-6 V/m (rms). The experiment could be run in either a Sun-sensor synchronized or a free state as controlled from the ground. In addition, the AC portion could be run in an averaging mode, or an alternating averaging and peak-amplitude-detection mode keyed to the telemetry readout sequence.
Electron and Proton Fluxes in the Outer Magnetosphere (1.5-300 keV) This experiment was designed to determine, by using identical instrumentation (see ISEE-2) 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 cylindrical 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.
Energetic Ion Mass Spectrometer (0-17 keV/q; 1 AMU to > 150 AMU) The objective of this investigation was to determine the ion composition and energy spectra of the plasma within the magnetosphere, magnetosheath, and solar wind, and to determine the angular distribution of the plasma in the magnetosheath. An energetic ion mass spectrometer was flown that had an electrostatic energy analyzer followed by a combined cylindrical electrostatic/magnetic mass analyzer. A combination of electron multipliers was used as the detector. The energy-per-unit-charge range measured was from 0 to 17 keV/Q. The mass-per-unit-charge range measured extended from 1 to 150 u/Q.
Fast Plasma Experiment (FPE) and Solar Wind Ion Experiment (SWE) This experiment was designed, in conjunction with a similar instrument (1977-102B-01) provided by G. Paschmann of Max Planck Institute for flight on the daughter spacecraft, to study the plasma velocity distribution and its spatial and temporal variations in the solar wind, bow shock, magnetosheath, magnetopause, magnetotail, and magnetosphere. The FPE consists of three high efficience 90° spherical section electrostatic analyzers using large secondary emitters and discrete dynode multipliers to detect analyzed particles. Two of them, viewing in opposite directions, produce complete 2D velocity distribution measurements of both protons and electrons every spacecraft revolution. A third FPE analyzer with a divided emitter measures 3D distributions at a slower rate. Protons from 50 eV to 40 keV and electrons from 5 eV to 20 keV were measured The experiment operated in two ranges, with energy resolution for the several steps in each range of 10% of the center energy level. The Solar Wind Experiment (SWE) measures solar wind ions. It is composed of two 150° spherical section analyzers using the same set of plates. The two acceptance fans are tilted with respect to each other so that 3D characteristics of the ion distributions can be derived. The ion experiment had degraded by April 1980 and the density values are suspected to be too low in later years. To protect the instrument, this experiment was turned off whenever the spacecraft was below . The Fast Plasma Experiment (FPE) had degraded by January 1978.
Gamma-Ray Bursts (Time History) This experiment was designed to recognize and record the time history of gamma-ray bursts. Two sensors were used: a -diameter, CsI scintillator system and a 6-cm2, solid-state (Cadmium telluride (CdTe)) array. An intensity increase in either of the sensors could cause a trigger signal to occur, freezing the circulating memory of the immediate past counting-rate history and filling another memory with the counting rates for 1 minute following the trigger signal. The time of the trigger signal and its location in the temporal history were also stored in memory. All stored information was then read out at a very low bit rate during the succeeding several hours. Three trigger signals were used based on total counts in 4 ms, 32 ms, and 256 ms. Six memories were used, three before and three after the trigger signal, yielding storage of 1/64, 1/8, and 1 minute of data each to provide detailed rise-time information.
Low Energy Cosmic Ray Experiment This instrument, carried on both ISEE-1 and ISEE-3, was designed to measure solar, interplanetary, and magnetospheric energetic ions in numerous bands within the energy range 2 keV/charge to 80 MeV/nucleon, and electrons in four contiguous bands from 75 to 1300 keV. At the lower energies, charge states of heavy ions in the high-speed (> ) solar wind were determined. In the range 0.3 to 80 MeV/nucleon, the energy spectra, anisotropies, and composition of energetic ions were determined. In the limited range 0.4 to 6 MeV/nucleon, simultaneous determination of ionic and nuclear charge was possible. The instrument consisted of three different sensor systems. "ULECA" (ultralow-energy charge analyzer) was an electrostatic analyzer with solid-state detectors. Its energy range was approximately 3 to 560 keV/charge. "ULEWAT" (ultralow-energy wide-angle telescope) was a double dE/dx vs E, thin-window, flow-through proportional counter/solid-state detector telescope covering the range 0.2 to 80 MeV/nucleon (Fe). "ULEZEQ" (ultralow-energy Z, E, and Q) was a combination of an electrostatic analyzer and a dE/dx vs E system with a thin-window proportional counter and a position-sensitive solid-state detector. The energy range was 0.4 to 6 MeV/nucleon. Data was obtained in 45° sectors.
Low-Energy Proton and Electron Differential Energy Analyzer (LEPEDEA) 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.
Medium Energy Particles Experiment (METE)