Resumen
Cooperative orbit determination (OD) using inter-spacecraft optical measurements is an important technology for space constellation missions. In this paper, the observability of a two-spacecraft cooperative OD system is investigated. The influence of geometric configuration on the observability is analyzed, and two special unobservable configurations are identified. Then, an approach to improve the observability by involving an additional spacecraft is proposed. Comparative analysis of system observability shows that an extra spacecraft in the system could change the coplanar and symmetric configuration and improve the observability of the cooperative OD system. Monte-Carlo simulations are carried out, and results verify the observability improvement conclusion.