Librational Stabilization of Electrodynamic Tethers using Time-Delayed Predictive Control

Paper number

IAC-07-C1.2.03

Author

Dr. Paul Williams, Australia

Year

2007

Abstract

Electrodynamic tethers may provide an efficient means for future in-space propulsion. It is possible to manipulate the orbit of a spacecraft by changing the current variation in the tether. Certain current variations provide a means of altering each of the spacecraft orbital elements. However, these variations can induce unstable librational motion of the tether.  The most popular concept for electrodynamic tethers is for deorbiting satellites at the end of their operational life.  In this case, a bare tether is deployed from the satellite to generate deorbiting forces.

One of the key problems for electrodynamic tethers is stabilization of the librational motion.  It is known that even for highly simplified rigid rod models of the system that the tether exhibits periodic solutions for a given current level.  However, these periodic solutions are unstable, with the instability growing as a function of the current level.  Previous research has demonstrated the ability to stabilize the tether around known periodic solutions, which requires a priori knowledge of the solutions.

This paper proposes a new feedback control scheme that is capable of stabilizing the librational dynamics of electrodynamic tethers using only modulations in the electric current.  The feedback does not require knowledge of the reference periodic solution, and as such, stabilizes the tether during orbital transfer.  The feedback controller is based on a time-delayed predictive control law, which chooses the electric current at the current sampling time to minimize the predicted librations of the tether from the librations that were measured during the previous orbit.  The control law is fully nonlinear and demonstrates convergence from large disturbances from the known periodic solution.  Numerical results are presented that demonstrate its applicability when the orbit of the tether system is changing over time.  In particular, the control law is able to handle both circular and elliptical orbits.

Abstract document

IAC-07-C1.2.03.pdf

Manuscript document

IAC-07-C1.2.03.pdf (🔒 authorized access only).

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