1766. The Gyro Dynamic Motion Simulator


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R L Marshner: 1766. The Gyro Dynamic Motion Simulator. 1987.



The GyroDynamic Motion Simulator (GDMS) is a facility that allows an inertially spinning system to move freely under the influence of internally generated moments. This is done by supporting the system on a zero friction gas bearing of hemispherical shape, and providing means to adjust the center of mass of the spinning system to coincide with the center of the gas bearing. The facility must be used under hard vacuum conditions to eliminate aerodynamic drag effects. Internal moments may be generated if a spin stabilized satellite system is non-rigid; for instance, if it includes active on-board personnel or partially filled containers of liquid. In the case of non-manned spin stabilized spacecraft, the internal moments generated by the ‘sloshing’ effect of fluid masses within the spacecraft cause a degradation in the stability. That is, they induce gyroscopic effects (precession and nutation) that can, in theory, eventually threaten the mission of the spacecraft. Since the energy contained by these disturbing motions is derived from the rotational energy of the spinning system, the spin rate of the spacecraft is slowed as the destabilizing energy increases. If the internal disturbances are continual, the result can be a slow but steady loss of spin rate and transfer of spin energy to unstable motions. Since a ‘sloshing’ fluid can easily dissipate energy by thermal changes in the fluid, it’s theoretically possible for the spacecraft to continually lose rpm as the spinning fluid mass tries to dampen the gyrations of the spacecraft. Loss of spin rate itself induces more degradation in stability, so over a long term the process can become catastrophic. The irony in this is that the principal cause of ‘slosh’ degradation is due to the liquid fuel carried for the maintenance of stability (needed to overcome the external influences). Spacecraft designers therefore need to know how much extra stabilization fuel must be carried to account for the destabilizing influence of the fuel itself.


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