SATELLITE-OBSERVATIONS AND INSTRUMENTATION FOR MEASURING ENERGETIC NEUTRAL ATOMS

Direct measurements of energetic neutral atoms (ENA) and ions have been obtained with the cooled solid state detectors on the low-altitude (220 km) three-axis stabilized S81-1/ stimulated emissions of energetic particles (SEEP) satellite and on the spinning 400 km X 5.5 R(e) (where R(e) is Earth radii) Combined Release and Radiation Effects Satellite (CRRES). During magnetic storms ENA and ion precipitation (E > 10 keV) are evident over the low-altitude equatorial region based on data from the SEEP (ONR 804) spectrometers and CRRES ion mass spectrometer (IMS-HI) (ONR 307-8-3) ion composition and ENA instrument. The IMS-HI neutral atom spectrometer covers the energy range from 20 to 1500 keV with a geometrical factor of 10(-3) cm2 sr and uses a 7-kG magnetic field to screen out protons less than about 50 MeV. During the strong magnetic storm of 24 March 1991 the first ENA and ion mass composition measurements were obtained of ring current particles below the inner belt and these fluxes are compared to the IMS-HI flux measurements in the ring current. Recently, an advanced spectrometer, the Source/Loss-cone Energetic Particle Spectrometer (SEPS), has been developed to image electrons, ions, and neutrals on the despun platform of the POLAR satellite (approximately 1.8 X 9 R(e)) for launch in the mid 1990s as part of NASA's International Solar Terrestrial Physics/Global Geospace Science (ISTP/GGS) program. To improve particle imaging by increasing sensor spatial resolution and sensitive area, a 256-element solid state pixel array having 6.25 CM2 area has been developed for SEPS along with three new low-power application-specific integrated circuit (ASIC) microcircuits.