Oscillating liquid propellant within a spacecraft's propellant tank is of concern when considering the attitude stability of the vehicle. As the oscillating liquid comes into contact with the sidewalls of the propellant tank, it releases small amounts of kinetic energy on the molecular level. The totality of this energy dissipation produces small forces and torques on the sidewalls of the tank resulting from the "fuel slosh"; namely the oscillating movement of liquid propellant taking place on the surface of the liquid. Fuel slosh, if not properly mitigated, has the ability to threaten the spacecraft's attitude control system (ACS) and compromise the validity of the spacecraft. Thus, initial spacecraft design requirements incorporate propellant management devices (PMD's) such as diaphragms into the propellant tanks. The diaphragms couple to the surface of the liquid and dampen the fuel slosh as it is taking place. However, even with preventative measures such as diaphragms, the adverse effects of fuel slosh can still persist if the propellant tank system is excited at its natural frequency. In this case, the sidewalls of the tank experience amplified forces and moments, rendering the diaphragm useless. Current research is directed at computationally modeling various fuel slosh scenarios which a spacecraft could potentially experience while in orbit. Simulations to be tested include, but are not limited to, different diaphragm materials within the tank, testing at the system's natural frequency, spin-up vs. spin-down maneuvers and propellant depletion scenarios. Upon acquiring sufficient and acceptable results from computational tests, similar models are created for experimental testing in the Embry- Riddle Aeronautical University Fuel Slosh Test Facility. Using the single axis linear actuator and fuel tank set-up in the test facility, experimental simulations are conducted with the intent to replicate the respective computational simulations. The research investigation aims at accurately correlating the results of the computational simulations with the results of the experimental tests. Similar results between the two types of simulations would add validity to computational methods becoming the primary means for modeling fuel slosh in initial spacecraft design. Additionally, by collecting data from a wide range of tests, the ERAU fuel slosh database can be populated with new results and correlations can be made from past and current simulations to better understand fuel slosh and its adverse effects on spacecraft.
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