Low-Gravity Fluid Dynamics Research on the International Space Station

Modern rocket science is concerned with improving the safety, reliability and performance of space exploration missions. A key challenge within the rocket science community is the accurate prediction of coupled fluid slosh and launch vehicle or spacecraft dynamics. Typically thermal-fluid engineers working on rocket science problems use Computational Fluid Dynamics (CFD) models calibrated with low-gravity, long duration slosh data and these data will improve the ability of rocket scientists and mission planners to develop higher performance and safer space propulsion vehicles.

The Florida Institute of Technology liquid slosh dynamics research team has previously performed a series of liquid slosh experiments in microgravity using NASA’s zero-g aircraft for rocket science applications. However, the “zero-g” aircraft platform provides only 20s of reduced gravity, and the interaction between the test tank and the aircraft’s acceleration during the climb phase of each parabola introduces complex dynamic effects. It would be ideal to start a “zero-g” experiment with the liquid as close as possible to stationary/parallel to the bottom of the tank. Slosh compensation techniques based on real-time acceleration feedback have been described in robotic applications, where pitch compensation is based on applying the acceleration necessary to make the total acceleration vector perpendicular to the bottom of the tank at any point in time. Compensation of the 2-D acceleration in the vertical plane (pitch) as the aircraft climbs would require control of two axes of motion, namely the pitch of the tank relative to the aircraft’s frame, and a translation along the aircraft’s main axis. Successful pitch compensation would allow reaching the zero-g portion of the parabola with the liquid as close as possible to stationary relative to the tank. If that could be achieved, several seconds of low gravity would be available, enabling the study of slosh during maneuvers of interest such as docking or nutation.

To explore the coupling of liquid slosh with the motion of an unconstrained tank in zero gravity, Florida Tech has teamed up with Massachusetts Institute of Technology (MIT) and NASA’s Kennedy Space Center’s (KSC) Launch Services Program (LSP) to perform a series of slosh dynamics experiments in the International Space Station (ISS)) using the SPHERES platform. The data collected from the experiments will continue to push the frontiers of rocket science.