Flight algorithms for autonomous tracking and navigation of distributed space systems using inter-satellite bearing angles
Keywords: Engineering.
Aeronautics and Astronautics.

Immense growth in usage of the space environment renders conducting mission operations between multiple resident space objects an increasingly necessary capability. Nevertheless, the application of distributed space systems to objectives such as space domain awareness, space debris management, satellite servicing, and planetary exploration presents new demands regarding the robustness and accuracy of navigation architectures and their overall autonomy, scalability, and flexibility. These demands must be met from the dual perspectives of mission design and on-orbit implementation. In response, this research investigates optical angles-only techniques for distributed space system navigation, in which observer spacecraft obtain bearing angles of target space objects using on-board cameras. Navigation subsequently becomes self-contained within the system with equal applicability to passive versus active targets and Earth-orbiting versus deep space missions. Less advantageously, bearing angles do not provide explicit target range information and are affected by optical visibility constraints, producing challenging observability conditions with complex dependencies on state and measurement properties. As a result, there are significant gaps to be bridged between the application of individual angles-only navigation algorithms in theory, thus far limited applications of angles-only navigation in flight, and the practical application of angles-only navigation to future distributed missions. These gaps are addressed by first developing a flexible approach for analyzing angles-only system observability. A system graph topology representation is combined with analytic and numeric methods to produce robust estimates of system navigation performance which are directly relatable to mission requirements. The method is fused with an optimization framework to enable intelligent, automatic optimization of distributed space system designs for angles-only navigation. In concert, a new tracking method is developed to enable acquisition of multi-target angles-only measurements in flight, using only sequences of monocular camera images. Multi-hypothesis methods and domain-specific kinematic modeling are leveraged to produce accurate target tracks with or without a-priori target state knowledge. The tracking method is integrated with batch and sequential orbit determination algorithms to formulate a complete architecture for distributed, autonomous angles-only navigation. The architecture is extended and generalized to perform navigation for distributed space systems in highly varied formation geometries and orbit environments. Performance of the architecture is verified across a suite of high-fidelity simulations with software- and hardware-in-the-loop. Finally, the architecture is integrated as part of the NASA Starling technology demonstration mission, which intends to be the first in-flight demonstration of autonomous angles-only navigation for a spacecraft swarm. Initial flight results for single observer/single target, single observer/multi-target and multi-observer/multi-target systems display promising navigation performance in support of future distributed space missions.