Orbital Design of Earth-Oriented Tethered Satellite Formations
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Orbital Design of Earth-Oriented Tethered Satellite Formations1 Steven G. Tragesser" and Ayhan Tuncay ' Abstract A formation of distributed sensors has great potential to enhance Earth surveillance. This paper investigates the dynamics of tethering several subsatellites together in a threedimensional configuration. To keep the system oriented toward Earth, the Likins-Pringle rigid body equilibria are used as a baseline design. A flexible lumped-mass model is used to assess the stability of the tethered system. Three parameters related to the formation size, masses and spin rate are varied in order to find designs that demonstrate desirable dynamic behavior. While none of the designs are Lyapunov stable, formations with a spin axis near the local vertical are well-behaved over time spans of several orbits.
Introduction Orbiting several small spacecraft in close proximity, referred to as formation flying, may dramatically increase the performance of remote sensing platforms. To minimize station keeping maneuvers of the formation, several researchers have proposed using tethers to maintain the satellites' relative positions [1]- [10]. To maintain stability of the tethered system, researchers have proposed either a "hanging" tether (aligned with the local vertical) or a spinning tethered system. The latter is optimal for interferometric applications because the dispersion of the satellites perpendicular to the observation direction can be maximized. This is achieved by aligning the angular momentum vector with the observation direction. An example of this type of application is the Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) mission proposed by NASA. One possible architecture has several collector satellites tethered together, spinning about the observation direction [1], [2]. The system will use optical interferometry in order to image deep space objects. IThis paper was presented as paper AIAA-2002-4641 at the AIAAJAAS Astrodynamics Specialist Conference, Monterey, CA, August 5- 8, 2002. 2Assistant Professor, Department of Aeronautics and Astronautics, Air Force Institute of Technology, WrightPatterson AFB, OH 45433. Currently: Assistant Professor, Department of Mechanical and Aerospace Engineering, University of Colorado, Colorado Springs, CO 80904. Email: [email protected]. 3Graduate Student, Air Force Institute of Technology.
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One of the earliest researchers on spinning tethered formations is DeCou [3], [4]. He investigated the dynamics of a triangular formation of satellites in which the spin rate of the formation is much larger than the orbital rate. The spin axis of these formations remains in approximately the same inertial direction and so this configuration is ideal for deep space observation. Several other researchers have also studied formations applicable to deep space astronomy [5] - [7]. This research considers the use of a tethered formation for terrestrial observation. This work is motivated by interferometric applications in which the satelli
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