Design of formation missions for Earth observation: relative motion model, validation, and application

This paper analyses orbit design for formation missions aimed at interferometric and bistatic SAR observations. To this end, a relative motion model is introduced and discussed, which builds on the orbital parameters approach and includes J2 secular perturbations. Numerical results show that an accuracy of 0.1% can be achieved both in the case of close formations aimed at crosstrack and along-track interferometry, and for large formations designed for bistatic acquisitions and characterized by distances of the order of hundreds of kilometers. In the former case, in fact, a first order approximation can be used with satisfying results, whereas second order terms allow to reach desired accuracy in the latter one. Furthermore, modeling errors are very stable in time. In the case of cross-track interferometry, formation design is performed for three frequency bands, achieving stable height accuracy and height of ambiguity along the whole orbit thanks to vertical and out-of-plane separation. It is shown how can relative trajectory deformation be used to the mission advantage. Some considerations about orbit design for along-track interferometry are also pointed out.