Mars Launch System and the Rotational Stability of a Prolate, Spin-Stabilized Spacecraft

This paper describes various analyses performed to characterize the rotational stability of the unguided second stage of the Mars Launch System, a key component of the planned Mars Sample Return campaign. The Mars Launch System is a two-stage solid rocket responsible for delivering select Martian samples from the surface of Mars into a tightly constrained orbit for rendezvous with the Earth Return Orbiter. Due to mass and geometry constraints, the second stage of the Mars Launch System would be unguided, prolate, and spin-stabilized. Under torque-free motion, a rotating body experiencing internal energy dissipation will tend towards its minimum-energy state rotating about its axis of maximum moment of inertia. As a prolate vehicle spin-stabilized about its axis of symmetry, any rotational energy dissipation from the Mars Launch System would negatively impact its directional stability. Therefore, it is essential to appropriately characterize and constrain potential sources of rotational energy dissipation and exchange in the system. Requirements on the structural modes of the vehicle can help prevent structural resonance with its rotational dynamics. However, some potential dissipative mechanisms, such as the motion of unconstrained Martian samples inside their collection tubes, are prohibitively difficult to prevent in the vehicle’s design. For these mechanisms, multi-body dynamic models have been developed to help predict the resultant impact of these mechanisms on the vehicle’s attitude stability. The results of analysis thus far have verified the feasibility of the Mars Launch System unguided, spin-stabilized second stage baseline implementation and have allowed guidance, navigation, and control simulations to better model the spacecraft’s stability throughout its burn and payload delivery. The decision to implement Mars Sample Return will not be finalized until the National Aeronautics and Space Administration's completion of the National Environmental Policy Act (NEPA) process. This document is being made available for information purposes only.