Sub-optimal, two-burn, mid-level thrust, LEO-GEO transfer mechanization and error analysis

The results of additional work performed at INTELSAT in the area of LEO-GEO transfer are presented. Previous work had produced an algorithm for the synthesis of two-burn, mid-level thrust, LEO-GEO transfer, the definition of the basic requirements of a constant rate steering law to approximate nominal trajectories, and the simulation of trajectories. This paper presents the details of an attitude control system concept for the implementation of the constant rate steering law and an analysis of the effects of the control system errors. The control system mechanization is centered around a set of three, single-axis, strap-down, orthogonal rate-integrating gyros, and a processor for the storage of pre-computed input commands and for the integrations required to re-orient the vehicle prior to each burn. The error analysis, based on an Intelsat VI application example, shows the GEO insertion errors resulting from the control system attitude errors at the beginning of each burn and from the rate errors.