Space Truss Zero Gravity Dynamics

Abstract : This technical report describes two truss experiments flown on the NASA KC-135 Reduced Gravity Aircraft. The purpose of these experiments was to investigate large space structure dynamics, ground test methods, and passive and active damping. A 2-meter truss was first flown to determine the rigid body dynamics in the aircraft during zero-gravity. The second flight's objective was to measure structural modes of a 12-meter truss, which represented a space structure component. Typically five to ten seconds of zero gravity data were recorded for each parabolic arc. Flight test results are compared with ground testing in which a low restraint spring mechanism was used to suspend the truss. Good correlation between ground and flight test results was achieved; the major differences were caused by suspension system friction, which coupled the frame modes with the bending and torsion modes.