Impulse-Momentum in Spacecraft Landing: Analysis and Experiment

Impulse-momentum methods of analysis developed for rigid body impacts are applied in this paper to predict forces acting in a simplified spacecraft model during a touchdown impact. This paper presents both analytic and experimental effort for a complex, multi-body impacting system that include friction and deformable elements. Specifically, we analyze a vertically moving guided mass representing a landing spacecraft to which is attached a telescopic, energy-absorbing leg. The landing gear, which is used in our study, employs crushable material in the leg, strut, and foot plus surface friction to absorb the landing shock. The experimental setup consists of simplified landing system, and accelerometers for the dynamic measurement. Acceleration data collected via data acquisition system is converted to the crushing, normal and tangential velocities. The results showed good agreement between the analysis and experiment for the first phase of motion. The derivation of limiting condition equations for all possible alternatives for the second phase is incomplete. We conclude that the challenges of deriving and testing for all motion phase ending events make the impulse-momentum method inferior to straight-forward dynamic simulation as a design tool.