The unpredictable behavior of liquid propellant inside a spacecraft's fuel tank is of great concern when considering the attitude stability of the space vehicle. The dynamic motion of the propellant, known as fuel slosh, is responsible for applying small forces and torques within a spacecraft's fuel tank, which can cause attitude and rate perturbations, nutation growth and ultimately compromise the mission. Fuel movement within the tank can also lead to an uncertainty as to the location of the spacecraft's center of gravity, and thus be problematic for accurate spacecraft attitude control. In order to control the unsteady motion of the liquid propellant, most fuel tanks are integrated with propellant management devices (PMD's), which work to control propellant position, dampen the fuel slosh and eliminate these unfavorable internal forces within the spacecraft. PMD's are often made from thin, visco-elastic materials that conform to the liquid propellant surface and deform as the liquid deforms. In order to gain a better understanding of the propellant motions and to develop more accurate, predictive analyses of spacecraft and launch vehicle dynamics, NASA's Launch Services Program (LSP) at NASA's Kennedy Space Center (KSC) has been sponsoring slosh research for the past decade. Laboratory testing using diaphragm PMD's is often costly and time consuming and is minimized whenever possible. As an alternative source of "test" data, computational fluid dynamics-based fuel slosh models are desired as they minimize the time and costs associated with an experimental test. They also allow data generation under environmental conditions not readily available in the laboratory, such as zero-gravity. Methods have been developed to extract parameters from the CFD generated data for use in simplified mechanical analog models such as the standard pendulum slosh model. This research begins with simplified computational and experimental models and intends to develop accurate, validated modeling methods for all combinations of propellant tank sizes and shapes, diaphragm/PMD types and shapes, fill levels and propellant types.
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