A Gravity Compensated Long Duration Orbit Transfer Guidance with Adaptive Ignition

Design of a closed loop guidance algorithm gets complicated as thrust from the propulsion system decreases considerably. Some of the assumptions made during the guidance algorithm design for an impulsive orbit transfer becomes invalid in case of a low acceleration system where the orbit transfer is achieved by means of a long duration burn. The long duration burn results in considerable loss of energy due to gravity/arc losses. Also in case of an elliptical to circular orbit transfer, the algorithm is very sensitive to its ignition point and a wrong ignition point manifests as severe eccentricity in the achieved orbit and excessive fuel consumption as well. This paper proposes a simple yet effective velocity based Gravity Compensated Long Duration (GCLD) Orbit Transfer guidance algorithm that accounts for the gravity/arc losses during the thrusting phase. The proposed algorithm caters for in-plane and out-of-plane requirements and thereby meets the targeted orbital conditions with minimal deviations. The paper addresses the difficulty of encountering inclination correction at points near the anti-node and it also proposes a kinematic condition based adaptive ignition logic which ensures that the targeted orbital conditions are achieved with reduced fuel consumption.