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P.E. Clark, M.E. Murphy (Catholic University of America), T.P. McClanahan (NASA/GSFC)
Scientific results from current work combined with technological developments in instrumentation and computing are advancing the use of X-ray spectrometry for remote planetary exploration. Remote X-ray spectrometry now plays a key role in the exploration of: 1) the Moon, the intended target of the ESA Smart-1 mission; 2) the large, S-class asteroid Eros, now the target of the NEAR mission; and 3) Mercury, the intended target of the Messenger mission. Missions have also been proposed for other small bodies. At present, primary requirements for remote X-ray spectrometry are: 1) The target has little or no atmosphere. 2) An X-ray source, generally the sun, is monitored onboard. 3) The source generates a sufficient signal/noise. This constraint is much less stringent for the intrinsically low cosmic ray induced background solid state detectors which are now replacing proportional counters. 3) The spacecraft trajectory has readily deducible target viewing geometries. Detailed knowledge of the source, spacecraft, target body, footprint positions and characteristics (e.g., roughness, degree of illumination, shadowing), as well as adequate (and possibly lengthy) signal integration times must be available. This necessitates more careful determination of acceptable trade-offs in spacecraft and instrument pointing capability, tracking frequency, fuel for active pointing, and cost than allowed by exclusively cheaper/ faster/ better approaches. Considerable improvements in data handling have resulted from our recent experience with large data volume and complex viewing geometries, including: 1) high speed interactive graphics capability for near real-time data monitoring; 2) the integration of models for source X-ray production with spatial information and real-time observations; 3) the incorporation of recently released high energy spectral analysis packages with background removal and peak detection assumptions that are flexible enough to be appropriate; and 4) the development of an interactive compositional database (Nittler et al, 2000) for analogous planetary materials which greatly enhances interactive modeling capabilities.
The author(s) of this abstract have provided an email address for comments about the abstract: Pamela.Clark@gsfc.nasa.gov