service-free all the time. In the latter case, we expect a rapid worsening in the optical properties to some extent (by loss of reflectivity and defocusing due to blistering) in the very beginning of operation, and subsequently a relatively long stable phase of operation. To overcome such effects and hence increase the foil performance and lifetime, we propose the following: 1. The mirror foil could have an Al coverage of at least 0.1 /xm thickness, corresponding to the maximum penetration depth of the solar particles. Thus, the possibly diastrous carbonization effects are largely avoided. This results, however, in an increase of the foil weight by at least 'At, and hence is a higher price. Therefore, this proposal seems to be reasonable only for small mirror areas. 2. After the setin of blistering, after complete foil carbonization, and later (typically every 10 years), the mirror should be covered with a thin fresh Al layer in situ. This could be easily accomplished by flying a furnace with evaporating Al along the foil surface at a certain distance. By this, the initial reflectivity is restored (smoothing of the blistered/flaked areas), and eventual brittle foil surface areas (flakes) are sintered together by the freshly evaporated material. Acknowledgement — We thank Dr. J.T. Chen for valuable discussions. We are obliged to Mr. Jesionek for his assistance in the foil irradiation experiment. REFERENCES 1. D. Fink, Uberblick uber die Meteoritenforschung, Stand 1983, HMI-report, HMI-B 138, 1974. 2. J.P. Biersack and L.G. Haggmark, A Monte Carlo Computer Program for the Transport of Energetic Ions in Amorphous Targets, Nucl. Instr. Meth. 174, 257, 1980. 3. J.P. Biersack and J.F. Ziegler, The Calculation of Ion Ranges in Solids with Analytical Solutions, in: “Ion Implantation Techniques” (ed. H. Ryssel, H. Glawischnig), Springer Series in Electrophysics 10, 157, 1982. 4. J.F. Ziegler, J.P. Biersack and U. Littmark, Empirical Stopping Powers for Ions in Solids, Proc, of the US-Japan Seminar on Charged Particle Penetration Phenomena, ORNL-report CONF-820131 82, 1982. 5. D. Fink, J.T. Chen, J.P. Biersack, M. Stadele, K. Tjan, S. Schlosser, C. Stumpff, Distribution of Light Ions and Foil Destruction after Irradiation of Organic Polymers, Proceedings of the MRS Europe Conference, Strassbourg, France, June 5-8, 1984. 6. D. Fink, J.P. Bieresack, J.T. Chen, M. Stadele, K. Tjan, M. Behar, C.A. Olivieri, F.C. Zawislak, Distributions of Light Ions and Foil Destruction after Irradiation of Organic Polymers, J. Appl. Phys. (in press). 7. T. Venkatesan, D. Edelson and W.L. Brown, Ionization Induced Decomposition and Diffusion in Thin Polymer Films, Nucl. Instr. Meth. 229 (Bl), 281, 1984. 8. M.C. Wintersgill, Ion Implantation in Polymers, Nucl. Instr. Meth. 229 (Bl), 595, 1984. 9. J. Davenas, X.-L. Xu and J.P. Thomas, Comparative Study of the Stability towards Ionic Irradiation of (CH)X and LiF, presented at the 2nd Inti. Conf, on Radiation Effects in Insulators, Albuquerque, N.M., May 30-June 3, 1983 (unpublished). 10. D. Fink, J.P. Biersack, M. Stadele, K. Tjan, R.A. Haring. A.E. de Vries, Experiments on the Sputtering of Group VI elements, Nucl. Instr. Meth. 229 (Bl), 275, 1984. 11. S.A. Richardson, P.L.F. Hemment and K.G. Stephens, Electrical and thermo-optical Properties of Ion Implanted Dielectric Films Used for Spacecraft Thermal Insulation, presented at the 2nd Inti. Conf, on Radiation Effects in Insulators, Albuquerque, N.M., May 30-June 3, 1983 (unpublished). 12. V. Shrinet, U.K. Chaturvedi, S.K. Agrawal and A.K. Nigam, A Simple Set-Up for In-Situ Observation of the Critical Dose of Blistering During Ion Implantation in Polymers, Nucl. Instr. Meth. 229 (Bl), 617, 1984.
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