964. Mass Property Control of a Synchronous Meteorological Satellite Scanning Experiment

Paper

Abstract

Spaceflight mission objectives may require both measurement and corrective control of the mass property parameters of
entire spacecraft or subassemblies. A scanning mirror assembly which is part of a Synchronous Orbit Meteorological Satellite is an example where mission objectives required measurement and control of weight, mass center, principal moments of inertia and products of inertia.
The scanning mirror oscillates within the spin stabilized spacecraft and both the scanning motor torque and perturbation of spacecraft attitude and spin rate have to be reduced to low levels. A theoretically ideal solution would be to make the mirror inertia constant about all axes in a plane perpendicular to the oscillation axis. A practically attainable compromise is to locate principal axes preferentially and make the difference between two of them acceptably small.
Methods for making the necessary mass property measurements and deriving and applying minimum weight ballast correction to achieve the necessary mass distribution are discussed. It is noted that mass property control operations are typically subject to practical constraints such as geometry and functional operation of the system and capability of available measurement facilities and fixtures.
Products of inertia can often be measured by spin balancing with more precision than Moment of Inertia measurements. Ambient gravity effects, whether useful or detrimental, require consideration. In many cases, tare properties of holding fixtures, interface fits and alignments, and precision of geometric definition of datum axes may be problem areas. The example described illustrates that achieving mass property control objectives requires appropriate assessment of all pertinent factors.