Computer Science – Performance
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsa23a1463f&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SA23A-1463
Computer Science
Performance
[0355] Atmospheric Composition And Structure / Thermosphere: Composition And Chemistry, [0358] Atmospheric Composition And Structure / Thermosphere: Energy Deposition, [0394] Atmospheric Composition And Structure / Instruments And Techniques
Scientific paper
The Wind and Temperature Spectrometer (WATS), developed at NASA-GSFC and NRL, is currently flying aboard the Atmospheric Neutral Density Experiment (ANDE). The primary mission objective of ANDE is validation and improvement of spacecraft drag and thermospheric models by measurement of the total atmospheric density. Drag determination also requires accurate measurements of neutral wind, temperature, and composition (O/N2 ratio). WATS provides the unprecedented capability to simultaneously measure all of these parameters in situ, by analyzing the angular and energy distribution of the gas stream passing its entrance aperture. WATS imposes very low power and size requirements on the host spacecraft, and is suitable for integration with small satellite platforms such as CubeSat. After passing through a pair of mutually-perpendicular collimating slits, neutrals are ionized by electron impact and energy analyzed by a crossed Small Deflection Energy Analyzer (SDEA) pair. The angular distribution of ions exiting the SDEA pair is measured by a microchannel plate (MCP) detector with linear spatial readout. The peak of this distribution indicates the neutral stream velocity vector in spectrometer coordinates, while the energy distribution yields the magnitude of this vector. Specification of the full neutral wind follows from knowledge of the satellite pointing angle. The width and shape of the angular distribution allows determination of the neutral temperature. Additionally, the high satellite velocity allows mass separation of the major thermospheric constituents by energy analysis. For example, at 7500 m/s, O and N2 have kinetic energies of 4.7 and 8.2 eV, respectively, and are readily resolved by the SDEA. This paper describes theoretical and experimental efforts aimed to characterize WATS performance, validate instrument and component functionality, augment sensor calibration, and improve data analysis. Much of this work has involved ion trajectory simulations (SIMION 3D) to characterize the operational parameters and performance of the crossed SDEA pair. Due to the intersecting SDEA volume and resulting potential field perturbations, energy analysis of low-angle ions traveling near the instrument axis requires greater voltages than predicted for a single SDEA. Additionally, the SDEA configuration in WATS includes an open drift region between the ion source aperture and analyzer entrance, which promotes ion beam divergence and yields less-than-ideal energy resolution. We present a promising deflection lens design predicted to collimate incident ion beams and significantly improve energy resolution. Also presented is experimental performance data for a novel low-power thermionic cathode (BaO-coated tungsten wire) that acts as the source of ionizing electrons in WATS. Additionally, ongoing laboratory experiments aim to characterize angle-dependent SDEA performance testing using a monoenergetic ion beam.
Dyer Justin S.
Fenn Dan
Finne T. T.
Herrero F.
Jones Heath
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