Dynamics Of Spinning Multi-Tethered Satellite Formations Containing A Central Body
- Paper number
IAC-05-C1.4.01
- Author
Mr. Ary Pizarro-Chong, McGill University, Canada
- Coauthor
Prof. Arun Misra, McGill University, Canada
- Year
2005
- Abstract
The concept of formation flying, with two or more satellites in a cluster, has been well investigated. Its applications are many, and entail scientific, military and civil objectives. Missions involving such systems (e.g., TechSat 21, ST5 Nanosat) are planned for the next few years. The satellites in these clusters are free-flying, which may place high demands on its attitude control system in terms of station-keeping as well re-configurability. Another concept, where the satellites are connected by tethers, could be advantageous. Multi-tethered systems have been the subject of a few studies, and the research has not been as involved. Multi-tethered formations could take many forms, including, for example, open-chains, rings and stars. In the present paper, we present research conducted on formations that contain a central body. The following description pertains to the simplest kind of formation, which can named hub-and-spoke (HAS). Here we have a central body (hub), from which stem N tethers (spokes), each having a satellite at its end. The closed-hub-and-spoke (CHAS) configuration is the same as that described previously, but the peripheral satellites are also connected in pairs with a tether. A double-pyramid-type configuration is also studied; this consists of a middle plane of ring satellites in a CHAS configuration, with one satellite above (anchor) and one below the middle plane. The anchors are also connected to every satellite in the middle plane. An assumption, which is probably realistic and practical in terms of control, is that the central body undergoes a circular orbit (in our research, at LEO). Under this simplifying assumption, it becomes possible to separate the orbital motion from the local motion. The tethers are assumed to be massless and to remain straight, but they are subject to elastic deformation and to structural damping. The equations of motion are derived using the Lagrangian approach. We examine configurations having between 3 and 5 bodies in addition to the central body. We look at spinning formations since the only stable non-spinning configuration is the one where all tethers are aligned along the local vertical. The planes of rotation which are examined are the orbital plane and the Earth-facing plane which is normal to the orbit. Analytical investigations were done along with numerical simulations. For rotation in the orbital plane, it was found it is possible for the hub-and-spoke formation (nominally in the orbital plane) to be stable, but the initial conditions must be chosen suitably. The CHAS configuration is nonetheless stable, since it compensates appropriately for the differences in the open formation. For rotation in the Earth-facing plane, neither a HAS nor a CHAS configuration (nominally in the normal plane) is stable. However, as was suggested in previous research, it is possible to have a configuration which is “elongated” along the local vertical (and thus uses the dumbbell as a basis for its stability), but spins in the normal plane. It was found that having a CHAS configuration (containing five bodies) in this manner is not stable because after some time, the ring satellites do not keep their relative angular distance. However, having a double-pyramid-type configuration of at least six bodies increases the stability of the configuration, as each satellite is connected by several tethers in a way that tends to avoid instability.
- Abstract document
- Manuscript document
IAC-05-C1.4.01.pdf (🔒 authorized access only).
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