1668. Mass Property Control of a Spin Stabilized Spacecraft With Restrictive Mission and Weight Constraints

Paper

Abstract

The San Marco D/L spacecraft has needed special analytical techniques and developmental tasks to achieve an acceptable mass property configuration for its mission. It will be launched and orbit in the equatorial region to conduct upper atmosphere studies. The primary experiment measures the drag effects on a light spherical shell coupled to a relatively massive center body and requires precise mass property control of both the shell and the center body. The centroids must coincide with each other and with the center of pressure of the shell and precise spin balancing is needed for launch and orbital stability. The spacecraft also has deployable antennas oriented along the nominal spin axis, which require accurate alignment, with compensation for antenna curvature. Accurate spin balance and adequate excess of spin axis moment of inertia over pitch axis moment of inertia are necessary to preclude the possibility of nutation induced antenna buckling.
When preliminary mass property measurements showed large products of inertia, an unfavorable spin to pitch inertia ratio, and a very low weight margin, a variety of corrective measures were developed and are detailed in this paper. Inertia booms and a yo-yo despin system were developed as add-on units; spin balance measurements about all three geometric axes were used to define weight minimized correction within the outer shell envelope, and boom tip mass differentials were optimized for the most favorable inertia ratio margin achievable within mission weight constraints. Weight versus orbital lifetime trade-offs were also considered.
The optimum solution for the use of boom tip mass differentials to reduce transverse inertia ellipse eccentricity to a minimum for the tip mass location constraint imposed by configuration geometry has general-purpose application for mass property control.