Orion: a Microsatellite Testbed for Formation Flying

A revolution in spacecraft guidance, navigation and control technology has started with GPS to autonomously provide spacecraft position, attitude and time information. This new technology is being applied to spacecraft constellations to achieve the precision formation flying required for many proposed science and commercial missions. These innovations will also result in significant reductions in weight, power consumption, and cost for future spacecraft attitude and orbit determination systems. Carrier-Phase Differential Global Positioning System (CDGPS) techniques can be used to autonomously track and then control the relative position and attitude between spacecraft. This sensing technology will enable the development of a virtual spacecraft bus where several spacecraft fly in close formation so that they can accomplish a common mission. This paper describes the capabilities being developed by merging the microsatellite and the CDGPS research at Stanford University. The focus of this cooperative laboratory effort at Stanford is on the Orion project, which will provide a low-cost microsatellite testbed to demonstrate precision formation flying. Introduction and Motivation Several future space science missions are driving the need for small, low cost satellites that can fly in formation and perform collaborative observations. Our approach to the spacecraft guidance, navigation and control uses Carrier-Phase Differential Global Positioning System (CDGPS) techniques to autonomously track and then control the relative position and attitude between the spacecraft in the formation. GPS can provide both vehicle position and timing information, and thus should result in significant reductions in weight, power consumption, and cost of future spacecraft attitude and orbital determination systems. This will also provide significant improvements in the capability of future microsatellites, and will allow them to be used in very complex missions. Recent results have demonstrated that Carrier-Phase Differential GPS (CDGPS) techniques can be used to autonomously track and then control the relative position and attitude between several spacecraft [18]. This sensing technology can be used to develop a virtual spacecraft bus using automatic control of a cluster of micro-satellites to replace the monolithic bus of current Earth Sciences Enterprise (ESE) satellites (such as Landsat-7) [3,6]. Many future space applications would benefit from using this formation flying technology to perform distributed observations, including earth mapping (SAR, magnetosphere), astrophysics (stellar interferometry), and surveillance. The goal is to accomplish these science tasks using a distributed array of many simpler, but highly coordinated, vehicles (e.g., microsatellites). The Space Systems Development Laboratory established in 1994 has been developing low cost microsatellites. The Aerospace Robotics Laboratory and the Space Systems Development Laboratory are now combining efforts to develop the technologies and hardware for a fleet of low-cost spacecraft to demonstrate precision formation flying. This combined effort is the NASA Goddard Space Flight Center sponsored Orion Project. Space Systems Development Laboratory The goal of the Space Systems Development Laboratory (SSDL) is to de-emphasize the large-scale method of thinking and replace it with the philosophy that space-faring vehicles can be designed and built to be smaller, faster, and cheaper, while still undertaking contributive tasks and experiments. Such satellites need to be small, lightweight, modular, and still offer full hardware support (power, CPU, attitude