LFT modelling for the analysis of relative motion controllers in eccentric orbits

Currently, circular orbit controllers are being developed for rendezvous & docking (RVD) and have acquired a high level of maturity. Nevertheless, the new exploration missions being envisioned, and for which elliptical orbit RVD presents appealingly advantages, indicate the need to explore the validity of these proven circular-orbit controllers for elliptical scenarios as well as the possibility of designing advanced elliptical RVD systems. In order to do this, it is essential to show that modern control techniques and tools (most based on the linear fractional transformation paradigm) developed for time/parameter varying and uncertain systems are mature and relatively straight-forward to use by the space industry. In this article, it is shown in a tutorial manner how these LFT techniques and tools are well suited to address all the pertinent issues while presenting the validation of a circular-orbit controller for elliptical orbits.