Jet-Damping and Misalignment Effects During Solid-Rocket-Motor Burn

The present study provides an assessment of the dynamical processes that take place during the solid-rocketmotor (SRM) burn of a spin-stabilized spacecraft. We discuss the equations of motion for a system consisting of a rigid-body spacecraft and the gases in the SRM combustion chamber without specifying a model for the gas flow. In particular, we exploit the conservation of angular momentum flux from the solid propellant to the combustion gases leaving the system. We obtain a rotational equation that contains the jet-damping and misalignment effects in terms of the mass flow center and the mean exhaust velocity that summarize the action of the gases on the system for any flowfield. Compact analytical models are established that incorporate these effects. Piecewise linear approximations are adopted for the evolution of the system mass properties with respect to time during the SRM burn .W ef ound that this technique is flexible and well suited for realistic time-varying system parameters. We illustrate the application of the model using the actual conditions of the CONTOUR spacecraft during its SRM burn on 15 August 2002. I. Introduction T HE principal effects that influence the pointing stability of a spin-stabilized spacecraft during the burn of a solid rocket motor (SRM) are induced by misalignment and jet-damping torques. The former category is caused by errors in the SRM thrust vector direction and/or center-of-mass (c.m.) offsets induced by spacecraft balancing and alignment errors. The jet-damping torque originates from the resistance of the outflowing gases against a transverse rotation.