Attitude Guidance Strategy Analysis for Geosynchronous Orbit SAR Satellite

Compared to Low Earth Orbit (LEO) synthetic aperture radar (SAR) satellites, geosynchronous orbit (GEO) SAR satellites have the advantages of wide swath, fast revisit, and continuous observation. Due to the influences of Earth rotation and satellite orbit parameters, such as inclination and eccentricity, the Doppler center frequency of the satellite borne SAR imaging is always non-zero while the attitudes of three axis remains nearly zero, resulting in degraded SAR image retrieval quality. The Yaw-Pitch two-dimensional attitude guidance strategy proposed by existing researches can achieve zero Doppler center frequency. But when the Yaw-Pitch guidance strategy applied to GEO satellites, the yaw angle significantly varies. Take the GEO orbit with 16° inclination for example, the yaw angle fluctuations from −82° to + 82°, causing great engineering design problems especially in energy, layout, etc. This paper proposes a Pitch-Roll two-dimensional attitude guidance strategy, which also achieves zero Doppler center frequency by realizing the same target pointing as the Yaw-Pitch guidance strategy. The pitch and roll angles variation range achieved by this method is much smaller, which is more favorable for engineering implementation.