Differential drag-based multiple spacecraft maneuvering and on-line parameter estimation using integral concurrent learning

In this paper, a set of low Earth orbiting spacecraft consisting of multiple chasers and a single cooperative or unknown target, is considered for rendezvous and along-orbit formation maneuvers. Each maneuverable spacecraft can change its experienced atmospheric drag acceleration by extending/retracting dedicated surfaces. A Lyapunov-based adaptive controller is designed using an Integral Concurrent Learning (ICL)-based adaptive update law and the Schweighart-Sedwick equations of relative motion to regulate the in-plane relative states of each target-chaser pair. The controller is designed to compensate for uncertainties in atmospheric density, drag or ballistic coefficient and the velocity relative to the atmosphere of each spacecraft in the fleet. When the system is sufficiently excited, the controller also provides estimation of the uncertain parameters. Numerical simulations using nonlinear dynamics for each spacecraft and the NRLMSISE-00 atmospheric density model, are conducted to validate the performance of the controller.