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'SPHERES' Tether Slosh Science Session #4 Scheduled For Mid-September
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'SPHERES' Tether Slosh Science Session #4 Scheduled For Mid-September

The fourth Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) Tether-Slosh investigation, dedicated to improving our understanding of how liquids behave when there is little to no gravity, will be carried out on the International Space Station (ISS) in mid-September 2018. Accurate prediction of coupled fluid slosh and launch vehicle or spacecraft dynamics (e.g., nutation/precessional movement about various axes, attitude changes, etc.) requires Computational Fluid Dynamics (CFD) models calibrated with low-gravity, long-duration slosh data. To explore the coupling of liquid slosh with the motion of an unconstrained tank in microgravity, the Florida Institute of Technology (FIT) has teamed up with the Massachusetts Institute of Technology (MIT) and NASA’s Kennedy Space Center to perform a series of slosh dynamics experiments in the ISS using the Ames SPHERES platform. The SPHERES testbed provides a unique, free-floating instrumented platform on ISS that can be utilized in a manner that would solve many of the limitations of the current knowledge related to propellant slosh dynamics on launch vehicle and spacecraft fuel tanks.

In the third SPHERES Tether-Slosh Science Session on August 9th, the crew ran a total of 17 tests with two different fluid tanks: a liquid-filled tank and a solid tank of same mass. While the test plan contained a variety of possible tests, the experiment focused specifically on tests 2 and 4 of the Test Plan to provide a good basis for the evaluation of fluid-induced dynamics. Test 2 showed expected dynamics with the liquid-filled tank and particularly changes in the .dynamics that were predicted in simulation when run with the solid tank. This qualitative evaluation is very promising and will be confirmed by analysis of the extensive data sets collected. Test 4 was run to evaluate the performance of closed-loop control of the tethered system and performed expected motions only in part of the runs, seeming more consistent with the solid mass tank. Proper performance evaluation will have to be based on the data, possibly leading to control strategy improvements that will be implemented in the final test. The telemetry and video data acquired during Tether-Slosh Science 3 will be analysed and compared with CFD simulations to highlight in the experimental setup the presence of effects already predicted in simulation. The evaluation of how the fluid and solid tanks affected the closed-loop control of the tethered system will inform future development of control strategies in the fourth and final test session of the program.

BACKGROUND: SPHERES are bowling ball-sized spherical satellites with power, propulsion, computers, and navigation that can be used for inspections, maintenance, spacecraft assembly, and other intravehicular operations. The ISS has been using three of them to conduct science and test a diverse array of hardware and software for more than a decade.

The SPHERES Tether Demonstration project onboard ISS will help with understanding tethering dynamics to capture loose objects and “space tug” chase vehicles in zero gravity. With this new capability, researchers will be able to improve computer programs and modeling needed for free-flying satellites to remove space debris and capture scientific samples from planetary objects on future deep space missions. The SPHERES Tether is a new integrated payload designed and developed by Airbus Defense & Space (Airbus DS) in collaboration with NASA and the Massachusetts Institute of Technology (MIT).

The SPHERES Slosh investigation examines the way liquids move inside containers in a microgravity environment. The phenomena and mechanics associated with such liquid movement are still not well understood and are very different than our common experiences with a cup of coffee on Earth. Rockets deliver satellites to space using liquid fuels as a power source, and this investigation plans to improve our understanding of how propellants within rockets behave in order to increase the safety and efficiency of future vehicle designs.

NASA PROGRAM FUNDING: Advanced Exploration Systems (AES) program, Human Exploration and Operations Mission Directorate (HEOMD)

ARC SPHERES TEAM: Jonathan Barlow, Jose Benavides, Jose Cortez, Robert Hanson, Simeon Kanis, Aric Katterhagen, Don Soloway, and Andres Vargas

POINT OF CONTACT: Jose Benavides, jose.b.benavides@nasa.gov

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