Environmental aspects of activities in outer space : state of the law and measures of protection : proceedings of an International Colloquium Cologne, May 16-19, 1988 organized by the Institute of Air and Space Law, University of Cologne in cooperation with the International Institute of Space Law and the Space Law Committee of the International Law Association / BöckstiegelKarl-Heinz, UniversitätKöln.InstitutfürLuft-undWeltraumrecht, ほか