Dedicated Slosh Dynamics Experiment on ISS using SPHERES (Advanced Space Operations in CR)

At the Kennedy Space Center (KSC) the Launch Services Program is leading an effort to conduct an experiment aboard the International Space Station (ISS) to validate computational fluid dynamics (CFD) models. As spacecraft missions get longer and more ambitious, it becomes increasingly important that we fully understand the location and movement of liquids inside the propellant tanks of these vehicles. It is essential to understand how the movement of the liquid propellant will affect the trajectory of the vehicle. Current CFD models should predict these dynamics, but because test data is lacking, the accuracy of the models is not well understood. The slosh experiment aboard the ISS sets out to acquire this type of data. 

The Synchronized Position, Hold, Engage, Reorient, Experimental Satellites – VERTIGO (SPHERES-VERTIGO) developed by the Massachusetts Institute of Technology (MIT)—are free-floating, soccer-ball-sized robots with their own propulsion and power. They are used aboard the ISS to study formation flight and other control system algorithms. For this experiment, these same SPHERES will be programmed with thruster firings that will emulate common maneuvers carried out by launch vehicles and spacecraft. This motion will impart energy to the fluid inside the experiment, which will measure its effects.  The ISS provides the perfect environment to conduct liquid behavior studies in microgravity. This investigation is planned to collect valuable data on how liquids move around inside of a container when external forces are applied to that container – this simulates how rocket fuels move around inside their tanks when motor thrusts are used to push the rocket through space. The slosh experiment takes advantage of hardware already on the ISS. The primary slosh experiment component is a clear, pill-shaped Lexan tank in the middle of the assembly. This tank is shrouded by a tan box designed to prevent the ISS ambient lights from interfering with the cameras. Also in the middle, is the center hub made of aluminum. This center hub has two arms to hold two high-resolution cameras. These cameras will collect video of the fluid inside the tank. The center hub assembly is connected to a larger frame, which connects to the two SPHERES units through a clamp system. VERTIGO computers attached to the SPHERES units will collect the data from the cameras and the onboard inertial measurement units. These computers are already on the ISS and will be used by the slosh experiment as storage and power for the cameras and accelerometers.