Dynamic Analysis of a Light Structure in Outer Space: Short Electrodynamic Tether
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The SET (short electrodynamic tether) is an extremely flexible deployable structure. Unlike most other tethers that orbit with their axis of smallest moment of inertia pointing towards the Earth's center (natural position), the SET must orbit with its axis of smallest inertia normal to the orbit plane. The Faraday effect allows the SET to modify its orbit in this position. This is due to the interaction of the Earth's magnetic field with the tether, which is an electric conductor. In order to maintain the aforementioned operating position, the SET is subjected to a spin velocity around its axis of smallest inertia. If the system were rigid, the generated gyroscopic pairs would guarantee the system's stability.
The tether is not perfectly straight after deployment. This fact could make the rotation of the structure unstable. The problem is similar to the instability of unbalanced rotors. The linear study of unbalanced systems predicts the structural instability once a certain critical velocity is exceeded. Instability is due to internal damping forces. The spin velocity of the SET is greater than the critical velocity. Nevertheless, certain works that include the geometric nonlinearities show a stable behavior under such conditions. The object of this paper is to try to verify these results for the SET.
The SET consists of a 100-meter tether with a concentrated mass at its end. The system has been modeled using the floating reference frame approach with natural coordinates. The substructuring technique is used to include nonlinearities in the system.
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