Guidance, Navigation, and Control for Formation Flying Using Differential Drag

Abstract

This work is concerned with the development of a scheme and algorithms for guidance, navigation and control, including attitude determination and control, for formation flying of small satellites via differential drag only along low Earth orbits. It includes \'real-life\' features: a high variability air density, an attitude control algorithm for ballistic coefficient modulation, an attitude determination algorithm processing gyroscopes and typical vector measurements, and several relative navigation filters using relative position sensing and based on various air density design models. The realistic GNC/ADC scheme is tested under high integrity conditions. It enables closure of an initial distance of 70 km down to 2 km within eight orbits for two nanosatellites on low Earth orbits similar to the International Space Station. The degradation in the performances as compared to an ideal guidance scheme is due to the high variability of an unknown air density, the relative navigation errors, and the attitude control errors, in order of dominance. The best relative navigation filter appears to be a robust H filter. A comparison of that filter with the various Kalman filters shows a quicker convergence, a lesser sensitivity to the jumps in the air density, a similar steady-state accuracy, albeit with a noisier behavior.