Abstract
An X-ray/gamma-ray spectrometer has been developed as part of a rendezvous mission with the near-Earth asteroid, 433 Eros, in an effort to answer fundamental questions about the nature and origin of asteroids and comets. During about 10 months of orbital operations commencing in early 1999, the X-ray/Gamma-ray Spectrometer will develop global maps of the elemental composition of the surface of Eros. The instrument remotely senses characteristic X-ray and gamma-ray emissions to determine composition. Solar excited X-ray fluorescence in the 1 to 10 keV range will be used to measure the surface abundances of Mg, Al, Si, Ca, Ti, and Fe with spatial resolutions down to 2 km. Gamma-ray emissions in the 0.1 to 10 MeV range will be used to measure cosmic-ray excited elements O, Si, Fe, H and naturally radioactive elements K, Th, U to surface depths on the order of 10 cm. The X-ray spectrometer consists of three gas-filled proportional counters with a collimated field of view of 5° and an energy resolution of 850 eV @ 5.9 keV. Two sunward looking X-ray detectors monitor the incident solar flux, one of which is the first flight of a new, miniature solid-state detector which achieves 600 eV resolution @ 5.9 keV. The gamma-ray spectrometer consists of a NaI(Tl) scintillator situated within a Bismuth Germanate (BGO) cup, which provides both active and passive shielding to confine the field of view and eliminate the need for a massive and costly boom. New coincidence techniques enable recovery of single and double escape events in the central detector. The NaI(Tl) and BGO detectors achieve energy resolutions of 8.7% and 14%, respectively @ 0.662 MeV. A data processing unit based on an RTX2010 microprocessor provides the spacecraft interface and produces 256-channel spectra for X-ray detectors and 1024-channel spectra for the raw, coincident, and anti-coincident gamma-ray modes. This paper presents a detailed overview of the X-ray/Gamma-ray Spectrometer and describes the science objectives, measurement objectives, instrument design, and shows some results from early in-flight data.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Adler, I., Trombka, J., Gerard, J., Lowman, P., Schmadebeck, R., Blodget, H., Eller, E., Yin, L., Lamothe, R., Gorenstein, P., and Bjorkholm, P.: 1972a, Science 175, 436.
Adler, I., Trombka, J., Gerard, J., Lowman, P., Schmadebeck, R., Blodget, H., Eller, E., Yin, L., Lamothe, R., Osswald, G., Gorenstein, P., Bjorkholm, P., Gursky, H., and Harris, B.: 1972b, Science 177, 256.
Boynton, W. V., Trombka, J. I., Feldman, W. C., Arnold, J. R., Englert, P. A. J., Metzger, A. E., Reedy, R. C., Squyres, S. W., Wänke, H., Bailey, S. H., Brückner, J., Callas, J. L., Drake, D. M., Duke, P., Evans, L. G., Haines, E. L., McCloskey, GF. C., Mills, H., Shinohra, C., and Starr, R.: 1992, J. Geophys. Res. 97, 7681.
Evans, L. G., Starr, R., Trombka, J. I., Brückner, I., Bailey, S. H., Goldsten, J. O., and McNutt, R. L., Jr.: 1996, 'Performance of the Gamma-Ray Detector System for the NEAR Mission and Application to Future Missions', Preprints of the Second IAA International Conference on Low Cost Planetary Missions, IAA-L-0905P, Laurel, Maryland, U.S.A., April 16- 19.
Evans, L. G. and Squyres, S. W.: 1987, J. Geophys. Res. 92, 9153.
Farquhar, R. W., Dunham, D. W., and McAdams, J. V.: 1995, J. Astron. Sci. 43, 353.
Gaffey, M. J., Bell, J. F., and Cruikshank, D. P.: 1989, 'Reflectance Spectroscopy and Asteroid Surface Mineralogy', in Asteroids II, University of Arizona Press, Tucson, pp. 98–127.
Gaffey, M. J., Burbine, T. H., and Binzel, R. P.: 1993, Meteoritics 28, 161.
Goulding, F. S. and Landis, D. A.: 1982, IEEE Trans. Nucl. Sci. 29, 1125.
Hawkins III, S. E., Darlington, E. H., Murchie, S. L., Peacock, K., Harris, T. J., Hersman, C. B., Elko, M. J., Prendergast, D. T., Ballard, R. W., Gold, R. E., Veverka, J., and Robinson, M. S.:' Multi-Spectral Imager on the Near Earth Asteroid Rendezvous Mission', Space Sci. Rev., this volume.
Hayes, J. R.: 1995, 'NEAR Instrument DPU Common Software Requirements Specification', JHU/APL, pp. 7358–9001.
Mandel'shtam, S., Tindo, I. P., Cheremukhin, G. S., Sorokin, L. S., and Dmitriev, A. B.: 1968, Cosmic Res. 6, 100.
McFadden, L. A., Gaffey, M. J., and McCord, T. B.: 1984, Icarus 59, 25.
Mosher, C. H.: 1976, IEEE Trans. Nucl. Sci. 23, 226.
Pieters, C.: 1976, Icarus 28, 105.
Santo, A. G., Lee, S. C., and Gold, R. E.: 1995, J. Astron. Sci. 43, 373.
Schneider, S. E.: 1995, X-ray/Gamma-ray Spectrometer DPU Software Requirements Specification, JHU/APL, pp. 7358–9002.
Trombka, J. I., Boynton, W. V., Brückner, J., Squyres, S. W., Clark, P. E., Starr, R., Evans, L. G., Floyd, S. R., Fiore, E., Gold, R. E., Goldsten, J. O., McNutt, R. L., Jr., and Bailey, S. H.: 1996,' Compositional Mapping with the NEAR X-ray/Gamma-ray Spectrometer', J. Geophys. Res., submitted.
Warren, J. W., Peacock, K., Darlington, E. H., Murchie, S. L., Oden, S. F., Hayes, J. R., Bell III, J. F., and Krein, S. J.: 1997, 'Near Infrared Spectrometer for the Near Earth Asteroid Rendezvous Mission', Space Sci. Rev., this volume.
Wetherill, G. W.: 1985, Meteoritics 20, 1.
Wetherill, G. W. and Chapman, C. R.: 1988, in J. F. Kerridge and M. S. Matthews (eds.), 'Asteroids and Meteorites', Meteorites and the Early Solar System, University of Arizona Press, Tucson, pp. 35–67.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Goldsten, J.O., McNutt, R.L., Gold, R.E. et al. The X-ray/Gamma-ray Spectrometer on the Near Earth Asteroid Rendezvous Mission. Space Science Reviews 82, 169–216 (1997). https://doi.org/10.1023/A:1005052720796
Issue Date:
DOI: https://doi.org/10.1023/A:1005052720796