Accession Number : AD0682308

Title :   INCLUSION OF TIME CONSTRAINTS AND REDUNDANT ACCESS ON SPACECRAFT RETURN PROBABILITIES BY THE CONCEPT OF BOREL SET.

Descriptive Note : Technical rept. Nov 67-Jul 68,

Corporate Author : AEROSPACE CORP EL SEGUNDO CALIF SYSTEMS ENGINEERING OPERATIONS

Personal Author(s) : Chu,S. T. ; Nagy,A. R. , Jr

Report Date : DEC 1968

Pagination or Media Count : 38

Abstract : Because of limitations of weather, sea state, and visibility, planning efforts for the emergency return by abort or escape from orbit to contingency recovery sites must consider factors of local time constraints and redundant access. The first factor provides a means of evaluating the impact of a daylight return requirement; the second permits appraising safer emergency recovery plans when unacceptable weather or sea state conditions exist at the initially selected recovery site. The return probability of spacecraft including these factors involves the determination of coverage belts along the equator that are generated by the loci of ascending nodes of orbits from which the recovery circle can be reached within the local time constraints and with the specified degree of redundancy in access. In general, the coverage belts collectively form a complicated and juxtaposed set. By using the linear Borel set concept, a logic is developed for properly counting and summing these belts to arrive at a general formulation for determining the return probability. Sample results show that the local time constraints have a significant effect upon the return probability. The seasonal variation of available daylight hours can also have pronounced influence on the return probability and the required waiting time for an assured emergency return if the recovery sites are in the same hemisphere. On the other hand, redundant access of the second degree, while having a lower return probability than single access, does not greatly increase the required waiting time for an assured emergency return of a spacecraft. (Author)

Descriptors :   (*SPACE FLIGHT, ABORT), (*ORBITS, *DESCENT TRAJECTORIES), RECOVERY, SET THEORY, VISIBILITY, PROBABILITY, TIME, MANNED SPACECRAFT, RESCUES, SITE SELECTION

Subject Categories : Astronautics
      Spacecraft Trajectories and Reentry

Distribution Statement : APPROVED FOR PUBLIC RELEASE