Reentry vehicle trim resulting from ablation coupled with motion

Reentry vehicles have been found to experience sudden changes in angle of attack, producing trajectory dispersions during significant ablation of the nosetip and heatshield. An explanatory wind tunnel experiment was performed to isolate the separate and combined effects of nosetip and afterbody ablation for a reentry configuration undergoing complex three degree of freedom (DOF) motion. Analyses of the data were performed by both a body fixed coordinate system and a rate gyro analysis method. A summary of test results is presented with an analysis of both a typical and an exceptional test run: ablating, camphor nosetips produced smoothly growing trims; erratic trim buildup occurred where both decreasing and increasing trim jumps were demonstrated; camphor noses with initial distortions produced smooth, rapidly growing trims, but not in the plane of the holes, and camphor afterbodies produced small constant trims; nonablating noses with gouges simulating boundary layer transition movement onto the nosetip produced small, constant trims. Results did not show, however, that the coupled three DOF motion and nosetip shape charge could explain the transient behavior observed in flight tests.