Gas-damper attitude stabilization for space tether systems
- Paper number
IAC-06-D4.3.08
- Author
Ms. Ana Blasco, European Space Agency (ESA)/ESTEC, The Netherlands
- Year
2006
- Abstract
The three-dimensional dynamics problem of a rigid body is usually analysed by dividing it into two other problems, the movement of the centre of mass (orbital problem) and the movement of the body relative to the centre of mass (attitude problem). When they are not coupled this approach results useful. Unfortunately, the coupling of theses two problems, even though being small, can result in highlighted effects on the dynamics. When electrodynamic tethers are used to provide thrust, a non-linear resonance appears and it is possible that it pumps energy into the system and it could have an effect on the system attitude dynamics. Depending on the orbital inclination, electrical density of plasma, and orbital parameters this effect can result in non-stabilized attitude motions of the system. In this paper a possible solution to eliminate instabilities of the electrodynamics tethers dynamics using a gas-damper is proposed. The development of tether technology during the last years has opened up an exciting new possibility for spacecraft completely propellantless propulsion. Rockets push against their own exhaust, but a conducting, electrodynamic tether allows a spacecraft to push against the Earth's magnetic field, transferring the rotational angular momentum of the Earth to the orbital angular momentum of the spacecraft. Two important applications of electrodynamic tethers, among others, are those of using them for deorbiting and propulsion. A crucial issue for both of the above applications is the dynamic stability of the tether system. The electrodynamic forces on the tether couple in fact in plane and out of plane oscillations and, especially for light systems, can drive the tethers unstable as has been shown in several numerical simulations. In order to eliminate the energy pumped into the system, completely or partially, the use of a gas-damper energy dissipater is studied in this paper. This mechanical device could be used to control tether oscillations. The standard piston-cylinder type damper with some modifications is used as an energy dissipater. The gas-damper is fixed to one tether end and has a point mass m (piston) with some small perforations. That mass moves along an axis parallel to the main direction. The cylinder contains helium that passes trough the piston perforations during the piston displacements and due to the helium viscosity the system dissipates energy in a controlled way. Also a spring and a classical damper, both with non-linear response fixed to the piston and the cylinder are added to study their influence on the dissipation process. After the analysis of the process using helium, other fluids will be analyzed in order to compare results. Varying the amount of viscous flow, the cylinder dimensions and the number and size of perforations on the piston, the damping coefficient of the gas-damper can be controlled. Parametrical analyses and also numerical simulations are carried out in this paper as a useful tool to optimize the energy dissipation process. It is also interesting to determine the damping ratio at which the total energy dissipated becomes maximum in order to be able to conclude if this gas-damper could be use to control the undesirable tether instabilities. If the results of this proposal are satisfactory enough to control tether instabilities, the gas-damper applied to tether attitude dynamics control could be one step to satisfy the needs of the science community in the areas of space tether attitude dynamics, precise pointing for interferometry, and planetary exploration.
- Abstract document