Sub-optimal, two-burn mid-level thrust, LEO-GEO transfer practical control schemes

The results are described of an algorithm developed at INTELSAT to: (1) synthesize sub-optimal, two-burn, mid-level thrust, LEO-GEO transfer trajectories, (2) define practical steering laws to approximate the nominal trajectories, and (3) simulate their performance. Capabilities of the algorithm include: independently selectable constant thrust levels for the two burns, constant acceleration, staging, fixing the mass at either ends of the transer. Figures of inefficiency versus ideally impulsive transfer are plotted for a reference constant thrust case over a range of initial accelerations. The diagram indicates that acceptable inefficiencies are attainable in the initial acceleration range above 0.1 g. A comparison with an optimal two-burn low-thrust transfer indicates negligible degradation in efficiency. The results of an application to INTELSAT VI are included.