Repeat-ground,track orbit acquisition and maintenance for earth-observation satellites

In this paper, the condition for repeat-groundtrack orbits is investigated. The analysis is based upon a set of orbital elements called epicycle elements. As well as avoiding circular orbit singularity, this analysis allows higher geopotential harmonics to be included up to an arbitrary number until a satisfactory accuracy has been achieved. It allows a repeat-groundtrack condition to be precisely evaluated with a simple and instructive mathematical description. In the second part of the paper, an orbit control strategy is proposed. Its aim is to autonomously maneuver a satellite from any initial condition toward a repeat-groundtrack condition. The emphasis is on a multiple-burn strategy with small velocity increments, which is preferable for small satellites for which the onboard and ground station facilities are limited. An autonomous orbit maintenance strategy to keep the satellite at a repeatgroundtrack condition despite perturbations from atmospheric drag is also presented. Finally, the, experimental results obtained from a 300-kg satellite are shown. Both the orbit acquisition and maintenance demonstrations confirm the performance of the proposed strategies.