Formation flying navigation exploiting inter-satellite radio link strength measurements

Formation flying missions require autonomous relative navigation, with an accuracy depending both on the mission goals and on the capabilities of the involved platform in terms of sensors and computation. The emerging, successful standard of Cubesat spacecraft represents a clear example of a platform introducing severe constraints. This paper aims to investigate the performance attainable by means of a simple solution for the relative navigation of the formations in Low Earth Orbit, especially suitable for moderate cost, moderate performance missions (like the ones exploited by cubesats). The solution builds on the radiofrequency inter-satellite link, and exploits both the received signal strength as well as the received signal shift in frequency. Related hardware is normally available in on board receivers, so that no additional equipment is required. Observables are fed to an estimator (Extended Kalman Filter) which on its turn poses really limited computational burden. The solution can be therefore conveniently intended as an inexpensive back-up or even as the primary solution for missions with rough requirements. Simulations for a number of interesting cases provide an insight about the actual performance to be attained with current hardware and correct filter tuning by means of this simple, traditional technique applied to formation relative navigation.