Jason D. Papastavrou and Michael Athans.Cover title. "This paper has been submitted for publication in the IEEE Transactions on Aerospace and Electronic Systems"--Cover.Includes bibliographical references (p. 17-19).Research was supported by the National Science Foundation (under a subcontract from the University of Connecticut) NSF/IRI-8902755 Research was supported by the Office of Naval Research. ONR/N00014-84-K-0519