Autonomous orbit determination using pulsars and inter-satellite ranging for Mars orbiters

In this paper, an innovative method for autonomous orbit determining combining X-ray pulsar measurement and inter-satellite ranging during Mars orbiting phase is presented. The use of X-ray pulsar measurement which can provide the baseline direction information for the satellites, combined with a high-precision inter-satellite relative range measurement can improve orbit determination accuracy. Firstly, the observability of the navigation system is analyzed. The results show that the observability of the navigation system is improved after adding pulsar measurement information and the state of the orbit direction is observable. Secondly, there are many restrictions on the observation of pulsars, such as the invisibility caused by the planetary occultation and avoiding zone due to the solar radiation. And the spatial orientation, target characteristics, the observation time and the measurement update frequency of the pulsars affect the navigation performance. Therefore, in order to improve the observability of the whole system, considering both the observation duration and the geometric configuration of the information source, an observability index reflecting the measurement information quality is proposed, then the observable target selection and observation scheduling are optimized. Finally, under the dynamic environment of Mars, the Unscented Kalman filter algorithm is used to simulate the autonomous pulsar assisted orbit determination for the typical orbit of relay navigation satellite and Sun-synchronous orbit. The simulation results show that, based on the optimized observation scheme, the proposed method can achieve high precision autonomous orbit determination. This method is suitable for rapid trajectory determination after orbit insertion and long-term autonomous maintenance of small constellations.