Autonomous Constellation Maintenance System

At present, a large number of surveillance, scientific, and commercial communications constellations are being actively pmsued by DoD, NASA, and the commercial space community. In many cases, these constellations will be made up of "LightSats" or small, low cost spacecraft. F or such systems, operations costs, which are large in traditional systems, can become a dominant element of total system life cycle cost. This implies a need for low-cost autonomous constellation maintenance in o:rder to allow such systems to be economically viable. A low-cost, autonomous approach for precisely maintaining the structure of Earth-orbiting satellite constellations from LEO to GEO is currently under development at Microcosm under contract with the U.S. Air Force Phillips Laboratory+. This work has significant heritage in previous internal and government-funded work at Microcosm. Utilizing hardware already onboard most spacecraft along with navigation and control software developed by Microcosm over the last 5 years, we can maintain each satellite in a constellation to within ±5 km of a desired, predetermined orbital position without requiring complex inter-satellite communication or ground-based commanding. The entire process is canied out onboard by each individual spacecraft. Because the system does not require crosslinks, initial satellites can be deployed directly into the constellation structure and the overall system has very soft failure modes. The net savings in total annual operations costs for a LEO constellation is potentially on the order of 10% to 20% over current practice. The concept ofa regularly scheduled (±0.7 sec) "Civil Orbit" will be introduced to illustrate how it greatly enhances some mission opportunities. This low-cost constellation maintenance system is described here, illustrating its range of • Copyright © 1996 by Microcosm, Inc . functionality and its application to different example constellations. The top-level system architecture is presented, showing the relation between the orbit control system and spacecraft attitude control system. Autonomous orbit control, the key system component which makes autonomous constellation maintenance possible, is also described. Simulation results are presented for the case of two satellites in the same orbit, separated by 10 sec in orbit phase.