Emerald: A low-cost spacecraft mission for validating formation flying technologies

Spacecraft formation flying is a proposed technology with vast performance implications ranging from enhanced mission capabilities to radical reductions in operations cost. To explore this concept and to enable its realization, Stanford University and Santa Clara University have initiated development of a simple, low cost, two-satellite mission known as Emerald. The Emerald mission has four primary goals. First, it will verify component-level technologies necessary for advanced formation flying missions. This will include the test of low-power Global Positioning System (GPS) receivers for position sensing, simple radio modems for inter-satellite communication, and experimental microthrusters for position control. Second, it will integrate the operation of these payloads in order to experiment with simple closed loop relative position control. Third, it will validate the formation flying concept by using coarse on-orbit relative position sensing and control to improve a scientific investigation of lightning-induced atmospheric phenomena. Fourth, it will extend low-cost satellite development techniques critical to fielding multi-spacecraft fleets. The bus design for the Emerald spacecraft will be based on Stanford's Satellite Quick Research Testbed (SQUIRT) microsatellite design. This consists of a 15 kilogram structure, a modular 12 inch tall by 18 inch diameter hexagonal configuration, a 68332-based flight processor, a single battery, solar panels, and simple attitude and thermal control. A Space Shuttle launch in 2001 has been tentatively selected for the launch of this mission. Emerald will be developed as part of the Defense Advanced Research Projects Agency (DARPA) and Air Force Office of Scientific Research (AFOSR) University Nanosatellite Program, an element of AFOSR's TechSat 21 Program. This paper discusses the Emerald mission objectives and approach, the conceptual design of the Emerald spacecraft, and the programmatic structure of this joint Stanford University-Santa Clara University project.