thin, space-qualified materials. This issue is not being addressed in current research programs. Data gathered to date indicate that the radiation tolerance of such thin-film materials is equal to or better than any other known photovoltaic materials. While much of the radiation data is preliminary or incomplete, it appears that in some high radiation orbits, thin-film materials may be the preferred technology even at present efficiency and specific power levels. Data on the behaviour of these devices in space are scanty. Even the efficiency information is extrapolated from terrestrial measurements, and needs to be verified in a rigorous manner using a spectrum calibrated for the specific material. For several missions, including solar-electric propulsion, a manned Mars mission, and lunar exploration and manufacturing, thin-film photovoltaic arrays may be a mission-enabling technology. ACKNOWLEDGEMENTS We would like to thank Ken Zweibel of SERI (whose review article on the use of thin- film cells for space [40] we highly recommend) for helpful discussions, and Kim Mitchell of ARCO Solar for providing several of the figures used here. REFERENCES [1] Flood, D.J. & Brandhorst Jr., H. (1988) Current Topics in Photovoltaics, Volume 2. [2] Baraona, C.R. (1986) Space Photovoltaic Research and Technology 1986, NASA Conference Publication 2475, Oct., 321-332. [3] Green, M.A., Wenham, S.R. & Blakers, A.W. (1987) 19th IEEE Photovoltaic Specialists Conference, 6-12. [4] Tobin, S.P. et al. (1989) 4th International Photovoltaic Science and Engineering Conference, Sydney, Australia, 14-17 February. [5] Ogasawara, N. et al. (1987) Tech Digest of the International PVSEC-3, Tokyo, Japan, 477-479. [6] ASEC (1987) Review of Mantech Program, December; see also P. Iles (1987) Manufacturing Technology for GaAs Solar Cells, Final Report, AFWAL-TR-87- 4092, Nov. [7] Ochi, S. et al. (1987) Tech Digest of the International PVSEC-3, Tokyo, Japan, 755-758. [8] Tobin, S.P. et al. (1988) IEEE Electron Dev. Lett., EDL-9(5), 256-258. [9] Vernon, S.M. et al. (1988) Space Photovoltaic Research and Technology, 179-189. [10] Tobin, S.P. et al. (1988) 20th IEEE Photovoltaic Specialists Conference, 405-410. [11] Khemthong, S. & Iles, P.A. (1988) Space Photovoltaic Research and Technology Conference, NASA Lewis, 19-21 April, 294-298. [12] Landis, G.A. (1988) 20th IEEE Photovoltaic Specialists Conference, 708-712. [13] Keavney, C.J. & Spitzer, M.B. (1988) Appl. Phys. Lett., 52, 1439-1440. [14] Weinberg, L, Schwartz, C.K. & Hart Jr., R.E. (1988) Space Photovoltaic Research and Technology Conference, NASA Lewis, 19-21 April, 17-26. [15] McClelland, R.W., Bozler, C.O. & Fan, J.C.C. (1980) Appl. Phys. Lett., 37, 560.
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