Satellite Reliability Estimation: Past and Present Procedures

Abstract

The satellite designer is particularly concerned with the reliability of certain “mission-critical” subsystems, since it is currently impractical to repair spacecraft in orbit. To insure long life the most reliable, space-qualified components must be selected and generally speaking, redundant subsystems must be provided even though the best available components are used. While many scientific or experimental spacecraft are required to perform a sequence of complex functions repeatedly over limited periods of time, the nature of the commercial satellite communications business demands a high probability of success for continuous operations over missions lasting many years. The earliest INTELSAT series of spacecraft had modest design life objectives ranging from 1 1/2 to 3 years. Starting with INTELSAT IV a 7-year life requirement was established as a design goal. This more stringent standard has continued with INTELSAT IV-A, INTELSAT V, and the INTELSAT V-A satellites, all (except the V-A) currently in commercial service for international communications. To achieve this standard, mathematical reliability models are employed to ascertain the soundest configurations, coupled with a very rigorous program of screening and burn-in of parts as well as severe derating (mechanical, thermal or electrical stress, and radiation, etc). Finally, any items which are subject to known wear-out or deterioration mechanisms must have a design life of at least 10 years.