"Hardware-in-the-loop Experiments of Precise Spacecraft Relative Navigation using Carrier-Phase Differential GPS"
Dr Jonathan P. How, Associate Professor at the Department of Aeronautics and Astronautics of Massachusetts Institute of Technology
Formation flying is an enabling technology for many future space science missions, but this approach can only be used if the relative states of the vehicles in the fleet can be precisely determined in real-time. This presentation will discuss recent results from hardware-in-the-loop experiments that demonstrate relative navigation for formation flying spacecraft. The approach uses Carrier-Phase Differential GPS, which provides an ideal navigation sensor for formation flying applications because it provides a direct measure of the relative positions and velocities of the vehicles in the fleet. A decentralized algorithm for formation estimation is presented, using an Adaptive Extended Kalman Filter to achieve unprecedented levels of accuracy. The experiments were performed using four modified GPS receivers in the NASA Goddard Formation Flying Testbed facility. Results from these hardware-in-the-loop tests show accuracies on the order of ~1cm position and <0.5mm/s velocity for a 1 km elliptical (passive aperture) formation. These results validate (i) the use of very simple dynamics models in the estimator, (ii) the selection of a decentralized estimation architecture, and (iii) the use of an adaptive EKF to estimate the noise levels in the system. The presentation will also discuss how we plan to demonstrate these algorithms and hardware on Orion using two microsatellites designed and built by students at MIT and Stanford.