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Meeting	ACGS Committee Meeting 119 - Fairborn, OH - March 2017
Agenda Location	7 SUBCOMMITTEE B – MISSILES AND SPACE 7.2 Satellite Formation Flying for Future Space Science and Exploration
Title	Satellite Formation Flying for Future Space Science and Exploration
Presenter	S. D’Amico
Affiliation	Stanford University
Available Downloads*	presentation
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Abstract	We propose the design, development, and high-fidelity validation of the Autonomous Nanosatellite Swarming Subsystem (ANS). ANS is an integrated miniaturized Dynamics, Guidance, Navigation, and Control (DGN&C) unit based on Commercial-Off-The-Shelf (COTS) avionics which is distributed and deployed on a swarm of cooperative nanosatellites to enable future military applications such as autonomous on-orbit surveillance, inspection, servicing, and aggregation. Previous on-orbit inspection and servicing missions such as DART (NASA), Orbital Express (DARPA), PRISMA (OHB/DLR/CNES), ANGELS (Air Force), or the planned DEOS (DLR), use a single large servicer spacecraft with active and expensive sensors such as radars or lidars for navigation. More recent low-cost developments such as for CAN-X 4&5 (University of Toronto) or CPOD (Tyvak/NASA) do not exploit the full potential of CubeSats and are fundamentally limited by the adoption of two satellites. These missions feature centralized DGN&C functionalities which are only partially automated in the terminal rendezvous phase, typically requiring heavy involvement from the ground and a-priori information on the target spacecraft’s orbit and/or three-dimensional (3D) model. In addition, traditional spacecraft DGN&C relies on impulsive control using legacy high-thrust monopropellant propulsion technology (e.g., hydrazine or cold-gas). In contrast to the state-of-the-art, the proposed ANS allows multiple nanosatellites to act together as a single large spacecraft thanks to precision centimeter-level radio-frequency/optical relative navigation using low-cost COTS sensors and actuator-agnostic control (from micro-Newton low-thrust to impulsive). ANS-equipped nanosatellites can fuse passive images of an unknown Resident Space Object (RSO) simultaneously taken from multiple viewpoints to achieve stereo vision capabilities with large and reconfigurable baselines. Depending on the target, these capabilities include the real-time on-orbit recovery of the three-dimensional model as well as the relative pose (translational and rotational) of the RSO at close-range (<1km) and absolute orbit determination of the RSO for space surveillance at far-range (1-100km) using angles-only measurements. ANS entails contributions to the state-the-art in the fields of relative astrodynamics, optical/radio-frequency navigation, optimal formation control, and their system integration. Specifically, new accurate and efficient closed-form propagation of the satellite relative motion in the presence of all perturbations of interest allow the design and coordination of swarms with exceptional long-term properties (safety, geometry, boundedness). Additionally, ANS employs for the first time a decentralized navigation architecture based on the deep fusion of optical and radio-frequency (RF) observables from multiple spacecraft that leverages the individual strengths of both measurement types. The measurements are obtained from a distributed customized nanosatellite sensor suite that includes two cameras for vision-based navigation at far-range (100-1km) to close-range (<1km), dual-frequency S-band transceivers for ranging and communication, and a Chip Scale Atomic Clock (CSAC) for precision timing and synchronization. Finally, the minimum propellant optimal control problem can be translated into a minimum length path-planning problem in the new state variables allowing for simpler and computationally faster solutions as compared to the state-of-the-art. In addition to allowing closed-form solutions for impulsive and extended maneuvers, the new problem formulation enables the enforcement of user-defined constraints in both the state and control input parameters. As a result, ANS represents a first-of-a-kind actuator-agnostic distributed control architecture.