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Slosh -Microgravity Fluid Slosh
September 22, 2013



SLOSH Experiment Overview



Brief Summary


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 engine designs.


Principal Investigator(s)


  • Paul Schallhorn, Aerospace Supervisor, Kennedy Space Center, FL, United States
  • Co-Investigator(s)/Collaborator(s)
  • Jacob Roth, Kennedy Space Center, FL, United States



Kennedy Space Center, , FL, United States
Massachusetts Institute of Technology, Cambridge, MA, United States

Sponsoring Space Agency

National Aeronautics and Space Administration (NASA)

Sponsoring Organization

Technology Demonstration Office (TDO)

Research Benefits

Information Pending

ISS Expedition Duration:

September 2013 - March 2015

Expeditions Assigned


Previous ISS Missions

Information Pending


Experiment Description

Research Overview

  • The SPHERES-Slosh investigation planned for the International Space Station (ISS) is dedicated to improving our understanding of how liquids behave when there is little to no gravity. Such an understanding is important because our most powerful rockets use liquid fuels to bring satellites into orbit.

  • Today, our best computer models still have not been carefully checked against actual experimental data on the behavior of liquids in microgravity. Unless our models are checked against real data, it is not possible to fully trust these models during rocket design and the planning of important space missions.

  • 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 data collected and the information learned from the analysis of that data impacts our ability to improve the performance of rockets and spacecraft. The data is used to check computer simulations about how rockets work, ultimately leading to rockets and spacecraft that are more reliable, safer and cost effective.

  • Finally, this investigation is being shared with middle school and high school students and teachers in a planned outreach program to continue to inspire the next generation of scientists and engineers.


Accurate prediction of coupled fluid slosh and launch vehicle or spacecraft dynamics (e.g., nutation/precessional movement about various axes, attitude changes, ect.) requires Computational Fluid Dynamics (CFD) models calibrated with low-gravity, long duration slosh data. Recently completed investigations of reduced gravity slosh behavior have demonstrated the limitations of utilizing parabolic flights on specialized aircraft with respect to the specific objectives of the experiments. Although valuable data was collected, the benefits of longer duration low-gravity environments were clearly established. The proposed research provides the first data set from long duration tests in zero gravity that can be directly used to benchmark CFD models, including the interaction between the sloshing fluid and the tank/vehicle dynamics.

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 International Space Station using the SPHERES platform. The Synchronized Position Hold Engage Reorient Experimental Satellites (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. The six degree of freedom (6-DOF) motion of the SPHERES free-flyer is controlled by an array of cold-flow CO2 thrusters, supplied from a built-in liquid CO2 tank. These SPHERES can independently navigate and re-orient themselves within the ISS. The intent of this project is to design an externally mounted tank to be driven inside the ISS by a set of two SPHERES devices. The tank geometry simulates a launch vehicle upper stage propellant tank and the maneuvers replicate those of real vehicles. The design includes inertial sensors, data acquisition, image capture and data storage interfaces to a single-board computer on board the flight article assembly. The design also includes mechanical and electronic interfaces to the existing SPHERES hardware, which include self-contained packages that can operate in conjunction with the existing SPHERES electronics.



Space Applications

The basic fluid slosh research and quantification that this project allows brings about a better fundamental understanding of low gravity fluid behavior. This understanding avoids problems like those seen on NROL-22, a National Reconnaissance Office satellite mission, where different fluid location predictions disagreed and forced a long launch delay before the differences could be reconciled. This inability to predict the fluid behavior can, at times, endanger the mission or at the very least, require excessive caution and helium reserves. A better understanding of fluid slosh could not only decrease uncertainty, but by extension, increase efficiency, reduce overhead, and increase payload up-mass.

Earth Applications

This project has a peripheral bearing on the average citizen of earth. In all, the propellant understanding produces a measurable increase in certainty of satellite life and functionality thus preserving satellite functions that the average citizen of earth relies on (e.g., telecommunications). Also, more abstractly, the results should provide a novel look at general fluid physics in a previously untested environment thus allowing the current physical laws and models to be checked and either confirmed or questioned. While we do not expect to find any new fundamental physics, the new environment broadens the scope of environments for which we have data to confirm our theories.



Operational Requirements

The SPHERES-Slosh investigation is required to operate in the volume of space currently available to SPHERES on the ISS. In addition, the testing requires the operational availability of any 2 SPHERES modules themselves with the appropriate amount of propellant and battery power. A single test session is defined to either remain within a specified time period (1 hour) or run until either the onboard data memory is full or one of the SPHERES runs out of propellant. It is currently estimated that ten test sequences are possible before any of these criterion are met, though this number is likely to decrease for longer test sequences, and also when crewmember operational and test sequence operational efficiency data is processed and understood. The current baseline is for test sessions to be separated by a minimum of one week, particularly for the early test sessions, so the data can be reviewed and future sessions altered if necessary to explore unforeseen phenomena. To complete the minimum goals of the project, it is estimated that 15 test sessions are required. The first two sessions are used for diagnostics and capability checks while the remainders are to perform a number of repeated maneuvers in order to examine the statistical behavior of each attempted maneuver. The only other major requirement is that the data be down-linked as soon as practical after every session using standard methods as currently employed by other on-ISS payloads. The data is stored in on-payload memory while awaiting down-link availability.

Operational Protocols

The SPHERES-Slosh investigation is computer controlled and requires only minimal interaction with the ISS crew. Depending on packaging and re-supply space requirements, some simple assembly may be required. Once the package is on station, an ISS crewmember takes the hardware out of the storage container and assembles a few pieces using simple lock-in-place hinges and rails. Once this operation is complete, the SPHERES units (already on station) are attached on both ends of the assembly. The SPHERES are attached using hand tightened screws that rigidly attach the test tank. Besides this, the ISS crewmember also connects any peripherals (cameras, IMU?s, hard drives, etc?) to the on-board computer using snap-in type connectors.

Once the unit is fully assembled, it is ready for research operations to begin. This simply involves an ISS crewmember powering on all units. This includes both SPHERES units, the on-board computer, and the SPHERES Laptop computer. Once all units are up and running, the entire assembly is placed in the center of the ISS module and allowed to free float. The ISS crewmember runs the software on the SPHERES Laptop which commands the SPHERES to perform a pre-specified set of maneuvers. After the test run is complete (5 minutes approx.), the unit is reoriented to the center of the module and a new test begins. Provided our allotted mission time allows, these tests continuously run until the on-board memory is full, or the CO2 propellant aboard the SPHERES runs out. Initial estimates show this to occur after about ten test sequences (1 hour approx). At this point, the crewmember attaches the hard drives to the SPHERES Laptop computer and downloads all of the test data for transmission back to earth.


Related Links


Florida Institue of Technology



Paul Schallhorn, Aerospace Supervisor,

SLOSH interfaced with 2 SPHERES
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Page Last Updated: September 25th, 2014
Page Editor: Darryl LeVasseur