Predicting the orbital lifetimes of Earth satellites

Abstract

Accurate prediction of the lifetimes of satellites decaying naturally under the action of air drag is one of the most difficult problems of orbital dynamics. Lifetime estimation is also a matter of practical importance when a satellite perceived as ‘dangerous’ is about to decay. The time when the satellite finally plunges into the lower atmosphere is affected by eight identifiable types of variation in upper-atmosphere density, by odd zonal harmonics in the gravitational field, and by possible changes in the mode of rotation of the satellite. We began predicting satellite lifetimes in October 1957, and we have since 1958 published a Table of satellites where lifetime estimates are given for all satellites, rockets and other major components (but not fragments). More than 10000 such predictions have been made. This paper summarizes the prediction methods used.