2300. Mass Properties Control Requirements for Step Mission 4

Paper

Abstract

The Space Test Experiment Platform (STEP) Mission 4 is a spinning spacecraft that depends on control of its mass properties in order to achieve the desired pointing. Test operations are performed during spacecraft integration to align the following three axes to the spacecraft geometric axis: Mass principal axis of the spacecraft body. Mass principal axis of the deployed wings. Momentum axis of the momentum wheel. The spacecraft includes an Inertial Properties Adjustment Device (IPAD) that can compensate for small residual errors in the axis alignments by making in-flightadjustments of a movable weight. The error terms associated with each test operation were first identified On a qualitative basis. The tests include a spin balance of the spacecraft body. They also include mass properties and shape measurements of the deployed wings that are not installed for the spin balance of the spacecraft body. Some of the errors could be quantified with high confidence. Others were engineering estimates with lower confidence. The final allocation of allowable errors and sizing of the minimum IPAD weight was made to meet the following constraints: Provide high confidence that the IPAD capacity will be sufficient. Provide test operations that are cost-effective and reliable.