Abstract. The FAST satellite mission investigates plasma electron beams, electrostatic shocks, ion beams and conics, processes occurring in the low altitude auroral acceleration density cavities, and numerous wave modes including auroral region, where magnetic field-aligned currents couple global kilometric radiation, ion cyclotron waves and VLF auroral hiss magnetospheric current systems to the high latitude ionosphere. and saucers. The time resolution of these measurements was In the transition region between the hot tenuous magnetospheric typically limited first by the spacecraft spin period, and ultimately plasma and the cold, dense ionosphere, these currents give risc to by telemetry capacity. In recent years, numerous sounding rocket parallel electric fields, particle beams, plasma heating, and a host experiments have revealed a broad range of important of wave-particle interactions.

The scientific objective of the NASA Small-class Explorer Mission SAMPEX are summarized. A brief history of the Small Explorer program is provided along with a description of the SAMPEX project development and structure. The spacecraft and scientific instrument configuration is presented. The orbit of SAMPEX has an altitude of 520 by 670 km and an 82" inclination. Maximum possible power is provided by articulated solar arrays that point continuously toward the sun. Highly sensitive science instruments point generally toward the local zenith, especially over the terrestrial poles, in order to measure optimally the galactic and solar cosmic ray flux. Energetic magnetospheric particle precipitation is monitored at lower geomagnetic latitudes. The spacecraft uses several innovative approaches including an optical fiber bus, powerful onboard computers, and large solid state memories (instead of tape recorders). Spacecraft communication and data acquisition are discussed and the space-and ground-segment data flows are summarized. A mission lifetime of 3 years is sought with the goal of extending data acquisition over an even longer portion of the 11-year solar activity cycle.

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