Angles-Only Onboard Initial Relative Orbit Determination with Auxiliary Satellite

Onboard initial relative orbit determination (IROD) by using angle measurements is the key to Space Situational Awareness. The camera offset measurement method is one of the most used IROD methods when only the angle measurement is available, which can overcome the range-observability problem caused by signal-camera measurement. However, the camera offset method cannot estimate the relative-position/-velocity when the chaser-target distance is much larger than the camera offset value, which is often below five meters. To overcome this problem, an auxiliary satellite treated as the chaser’s camera with known offset is proposed in this paper, which is suitable for satellites without cameras, and the IROD algorithm is also conducted correspondingly. The Tschauner–Hempel relative orbital motion dynamics and measurement model are given first. Then the IROD algorithm is yielded as a compact form by using the state augmentation least square method. Finally, a two-body satellite’s orbit dynamics model is built to generate simulation data, and three scenarios are studied to verify the convergence of the proposed IROD algorithm. Simulation results validate the proposed IROD algorithm converges quickly, and the measurement time corresponding to the lowest relative-position estimation error is related to the distance among the target, the chaser and the auxiliary satellite.