Finite thrust transfers

The purpose of this paper is to analyze orbit transfer strategies, assuming a propulsion module of finite and constant thrust capable of delivering multiple burns. Several thrust-steering laws are considered for the transfer between circular orbits (coplanar and noncoplanar) and apogee boost motor firing: (1) fuel-optimum unconstrained thrust direction applying Pontryagin's Maximum Principle, (2) inertially fixed thrust direction, (3) thrust direction constant in orbital frame, and (4) constant rotation of thrust vector around a fixed rotation axis. The suboptimum strategies (2) to (4) often prove to be competitive with strategy (1) in terms of fuel consumption. The attitude control laws resulting from strategies (2) to (4) are in general better suited for practical implementation. The performance losses due to finite thrust are relatively small for both transfer classes considered.