Numerical Simulations on the Stable Tether Deployment prior to the Activation of the Conductive Tether System for the Debris Mitigation
- Paper number
IAC-05-C1.4.02
- Author
Mr. Shoichi Yoshimura, Japan Aerospace Exploration Agency (IAT/JAXA), Japan
- Year
2005
- Abstract
An in-house study is being carried out on the on-orbit verification test of the electrodynamic tether(EDT) system for the debris mitigation. Space debris problems including debris mitigation measures are being studied in the various organizations in Japan. The studies have shown that the EDT system would be a potential propulsion system for the debris de-orbit. It has led to a realization that the operation of the EDT system in space should be verified at an early stage. Before the activation of the EDT system, the tether should be deployed stably along the local vertical direction, in order to avoid the rapid growth of instability in the three dimensional libration of the tether system caused by the electrodynamic force. In this study, the deployments of the 5 km/10 km-long conductive tethers before the passage of an electric current have been numerically simulated in the circular orbit of 300 km altitude and 52 degrees of inclination, assuming the second stage(3400 kg) of H2A, Japan’s launching vehicle, as a probable and stable platform of 50 kg sub-satellite. In the simulation, an oscillation-damping tension control law and the following station keeping tension control law have been introduced. The orbital dynamics has been simulated in the Earth’s gravity field including J2 term, adopting the following assumptions: mother satellite and sub-satellite are modeled as the point masses, respectively, and tether as a massless hinge. The main assumptions are: (1) Sub-satellite is ejected earthward. The event of ejection is specified by an addition of the ejection velocity at the instant of ejection. (2) Both deployed length L and deployment rate dL/dt of the tether are known(measured). (3) Tension Tc can not be applied in negative dL/dt even after the tension control began. (4) The level of the applicable tension does not depend on the EDT sections, although EDT is to be composed of the different segments and materials(bare/insulated conductive sections and non-conductive sections). Through the preliminary simulations, the ejection velocities Ve large enough for the 5 km/10 km deployments and the corresponding reeling-out frictions Trf are specified: (1) Ve =1.5 m/s, Trf =0.08 N, and for conceivable larger Trf, (2) Ve =2.0 m/s, Trf =0.10 N, (3) Ve =2.0 m/s, Trf =0.12 N, for both 5 km and 10 km deployments. Being ejected earthward, the sub-satellite leaves away from, below, and ahead of the mother satellite. The deployment rate dL/dt decreases caused by Trf at the initial phase. Then, the gravity gradient force overtakes the other forces such as Coriolis force, and a shape of the blunt corner develops in the relative position history. An in-orbital plane libration angle theta of the tether system takes a maximum value at that corner. When the deployed length L exceeds the specified command length Lc1, the oscillation-damping control is activated. The sub-satellite continues to go ahead for a while, and then begins to go back toward the local vertical direction. When L exceeds another specified command length Lc3, slightly shorter than the target deployment length, the control mode is switched to the station keeping mode. After that, the 5 km/10 km deployments are attained. Then, the sub-satellite moves to the stable in-orbital-plane oscillation mode with small to-and-fro amplitude. The 5 km and 10 km deployments are attained within about 0.65 to 0.84 orbital revolutions. The residual peak-to-peak amplitudes of theta are within about 4.0 degrees for the 5 km deployment, and around 10.0 degrees for the 10 km deployment. The magnitudes of the applied control tension Tc for 5 km/10 km deployments are about 2.7/6.5 N in peak and about 2.5/5.0 N in the stable phase, respectively. The out-of-orbital-plane oscillation angle psi stays within the ranges of –0.15 to 0.16 degrees, one order of magnitude smaller than theta, for both 5 km and 10 km deployments. The contents of this study are plain for the colorful visual appeal of a poster. Author prefers an aural presentation to a poster presentation.
- Abstract document
- Manuscript document
IAC-05-C1.4.02.pdf (🔒 authorized access only).
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