Mission description

ISEE 1 And 2 were launched together on 22 October 1977 and followed the same highly elliptical geocentric orbit (23 R_E by 270 km), with a small but variable separation between the two to separate spatial from temporal effects in the observations associated with measurements by a single spacecraft on thin boundaries which may be in motion. Such boundaries include the bow shock and the magnetopause. During the course of the mission, both ISEE 1 and 2 orbit parameters underwent short-term and long-term variations due to solar and lunar perturbations. By maneuvering the ISEE 2, the inter-spacecraft separation as measured near the Earth's bow shock was allowed to vary between 10 km and 5000 km. Its value is accurately known as a function of time and orbital position. The spacecraft were spin stabilized, with the spin vectors maintained nominally within 1 degree of perpendicular to the ecliptic plane, pointing north. The spin rate was nominally 19.8 rpm (19.75 for ISEE-1), so that there was a slow differential rotation between the two spacecraft. The ISEE 2 body-mounted solar array supplied approximately 112 W at launch. The data rate was 2048 bps most of the time and 8192 bps during one orbit out of every five (with some exceptions).

The satellites passed through the magnetosphere and into the magnetosheath during each orbit.

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 and mechanisms operating in the plasma sheets;
4. to continue the investigation of cosmic rays and solar flare effects in the interplanetary region near 1 AU.

Both spacecraft re-entered the Earth's atmosphere during orbit 1518 on 26 September 1987. Seventeen of 21 on-board experiments were operational at the end.

Detector description

The KED experiment was designed to identify and to study plasma instabilities responsible for acceleration, source and loss mechanisms, and boundary and interface phenomena throughout the orbital range of the mother/daughter satellites. A proton telescope and an electron spectrometer were flown on each spacecraft to measure detailed energy spectra and angular distributions.

The KED instrument utilized solid state detectors and magnetic analysis to measure the angular, energy, and intensity distributions of protons (ions) greater than 24 keV and electrons greater than 20 keV. KED on ISEE 2 consisted of five sensors mounted at various angular positions with respect to the spacecraft spin axis. The two sensors are a WAPS (Wide Angle Particle Spectrometer) similar to the one located on the WIM instrument and a Narrow Angle Particle Spectrometer (NAPS). NAPS utilizes a homogenous magnetic field to seperate the electrons from the ions. The ions traverse the field unaffected and are detected in a similar fashion as the WAPS. The KED instrument provides less detailed angular resolution with a multiple sensor head, but higher time resolution (4,16, or 32 samples per spin, dependent on bitrate and mode).

Figure 1. Sketch of the KED instrument [From Williams et al., 1978]

The KED instrument was designed and constructed by The Max-Planck-Institut fur Aëronomie (MPAE) with input and assistance provided by The Institute fur Reine und Angewandte Kernphysik, University of Kiel (KIEL) and The NOAA Space Environment Laboratory (SEL).