Effects of Propellant Slosh on Touchdown Stability for Landing Vehicles

This paper aims to characterize the effect of propellant slosh using a multistep analytical method for the two-and-over and two-two-and-over passive landing modes. Each touchdown of a landing leg is modeled as an inelastic collision, which is analyzed using generalized impulses and generalized momenta. Simulation results establish conditions at which slosh improves or degrades touchdown stability compared to treating the system as a single rigid body. Because slosh is generally uncontrolled but bounded, this study establishes a rule of thumb for designers to use in adjusting the vehicle height or landing-leg footprint in order to maintain stability in the presence of slosh dynamics when operating close to the stability boundary.