HR: 1400h
AN: SA33A-02    [Abstracts]
TI: Measuring Atomic and Molecular Species in the Upper Atmosphere up to 1000 km with the Free-Fall Mass Spectrometer and the Small Deflection Energy Analyzer
AU: * Herrero, F
EM: fred.herrero@nasa.gov
AF: NASA Goddard Space Flight Center, Detector Systems Branch Code 553, Greenbelt, MD 20771, United States
AU: Nicholas, A
EM: andrew.nicholas@nrl.navy.mil
AF: Naval Research Laboratory, Space Science Division Code 7607 4555 Overlook Avenue, Washington, DC 20375, United States
AB: Atomic oxygen (O), the major constituent of the Earth's thermosphere above 200 km altitude is both a driver and a tracer of atmospheric motions in the thermosphere and plays a pivotal role in interactions with the ionosphere through ion-drag and chemical reactions. At altitudes above 400 to 500 km, the energies and composition may reveal interactions with the magnetosphere. In addition, satellites in low-Earth orbit require knowledge of O densities to address engineering issues in low-Earth-orbit missions. The major difficulties in O measurements involve ambiguities due to the recombination of O in the sensor surfaces to yield O2 which is then measured with a mass spectrometer; similar difficulties exist for atomic hydrogen H and nitrogen N. In this paper we describe the use of our new charged particle spectrometers to measure relative densities and energies of the neutral and ion constituents in the upper atmosphere and into the exosphere to about 1000 km altitude. Neutral atoms are ionized before striking internal surfaces and surface-accommodated atoms and molecules are discriminated from incident ones according to their energies. Our ion source sensitivity is about 1.3x10-4/s per microAmp electron beam current for a number density of 1/cm3. Thus, operating with 1 mA emission (about 0.2W cathode power), signals of 100/s with integration period of 1 second correspond to a neutral atom density of about 103/cm3 with 10% variance. At very high altitudes, the lowest densities occur with the coldest thermopause - a 750K thermopause having an O density of about 150/cm3 at 1000 km, much higher densities for H and He, and much lower for O2 and N2. Total power for the spectrometer suite is less than 0.5 W with a mass of about 0.5 kg, based on our current versions. We plan to propose development of the sensor suite for two missions; one at 400 km and one at 830 km.
DE: 0328 Exosphere
DE: 0394 Instruments and techniques
DE: 2419 Ion chemistry and composition (0335)
DE: 2716 Energetic particles: precipitating
DE: 2736 Magnetosphere/ionosphere interactions (2431)
SC: SPA-Aeronomy [SA]
MN: 2007 Joint Assembly