A Trim Mass Would Be Manipulated by six electromagnets located on the axes of a Cartesian coordinate system.

Systems of caged trim masses manipulated by magnetic fields have been proposed for effecting fine control of the positions and/or orientations of spacecraft. The systems were conceived for use during observations by spaceborne interferometers, the component instruments of which (1) are located on multiple spacecraft flying in formation and (2) are required to be kept aligned with each other within narrow position and orientation tolerances. The proposed systems would make it possible to avoid the spurious effects generated by the spacecraft propulsion systems that would otherwise have to be used for fine position control; the spurious effects would include vibrations, exhaust, and flashes of light, which would be detrimental to the interferometric observations. Terrestrial versions of the proposed systems might be useful for fine horizontal positioning of delicate scientific instruments.

Three caged trim masses would be needed for complete position and orientation control of a spacecraft in three dimensions. Each trim mass would be manipulated by three pairs of opposing electromagnets — one pair for each of three mutually orthogonal axes (see figure). During times when observations were not being performed (e.g., during use of the spacecraft thrusters), the electromagnets would be activated to reset the trim masses to, and hold them at, the central positions within their cages.

This work was done by James Kelley of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Mechanics category. NPO-20570

This Brief includes a Technical Support Package (TSP).
Magnetically Moved Trim Masses for FIne Position Control

(reference NPO-20570) is currently available for download from the TSP library.

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