SPHERES Tether Slosh (SPHERES Tether Slosh) - 01.16.19

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
SPHERES Tether Slosh combines fluid dynamics equipment with robotic capabilities aboard the International Space Station to investigate automated strategies for steering passive cargo that contain fluids. In space, the fluid fuels used by spacecraft can slosh around in unpredictable ways making space maneuvers difficult. SPHERES Tether Slosh uses two Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) robots tethered to a fluid-filled container covered in sensors to test strategies for safely steering spacecraft such as dead satellites that might still have fuel in the tank.
Science Results for Everyone
Information Pending

The following content was provided by Hans Juergen Zachrau, and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom: SPHERES Tether Slosh

Principal Investigator(s)
Hans Juergen Zachrau, Airbus DS Space Systems, Inc., Webster, TX, United States

Philipp Behruzi, Ph.D., Airbus, Bremen, Germany
Daniel Kirk, Ph.D., Florida Institute of Technology, Melbourne, FL, United States

Airbus DS Space Systems, Inc, Webster, TX, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
National Laboratory (NL)

Research Benefits
Earth Benefits, Space Exploration, Scientific Discovery

ISS Expedition Duration
September 2017 - March 2019

Expeditions Assigned

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • SPHERES Tether Slosh aims to actively steer a passive body in space containing liquid.
  • The presence of liquid creates disturbance and unbalance, especially with changes in a liquid’s (CoG) center of gravity.
  • A reliable prediction of liquid disturbance and unbalance are necessary in scenarios such as that of the passive removal of a satellite where the towing spacecraft may contain large amounts of liquid thus requiring unique maneuvers.
  • The International Space Station (ISS) environment enables testing of SPHERES Tether Slosh and based on results software may be verified or updated.


SPHERES Tether Slosh investigates slosh dynamics in microgravity while allowing crew members to perform repetitive and different scenarios during one session, a major step forward in mathematical model development and validation. A simulation tool called Final Phase Simulator (FiPS®) is available, however, it lacks experimental validation with on-orbit flight experiments. FiPS® is the back bone for evaluating ballistic flight phases which include propellant sloshing. Generally, the tool is used for Sloshing assessments in launcher upper stages, satellites (e.g. high pointing accuracy missions), and are proposed for simulating missions concerning debris removal, e.g. for deorbiting stranded satellites. Further applications with respect to sloshing in airplane wing tanks are presently under consideration.
The FiPS® tool includes all important aspects of orbit flight which are the rigid body dynamics being disturbed by the liquid sloshing in the tanks (center of gravity shift and disturbing sloshing forces), as well as guidance, navigation and control which need to control and balance the disturbances. The tool is able to simulate the anticipated flight scenarios and is aimed to evaluate the feasibility of a debris removal mission. For this purpose, proper flight experimental data is needed.

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Space Applications
The sloshing liquid in the tank of spacecraft is a disturbance accounted for by the maneuvering of SPHERES satellites connected to the uncontrolled slosh tank. Test findings are of value for any kind of uncontrolled spacecraft where disturbances and uncertainties in respect to the CoG need to be taken into account. The test is a step towards developing a technology to deorbit passive objects in space.

Earth Applications
The interactions between sloshing liquid and rigid body dynamics and control are a challenge from ships to spacecraft. Simulation tools which predict these challenges are under development. SPHERES Tether Slosh tests these tools in a challenging environment, improving them for application in space and on Earth alike.

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Operational Requirements and Protocols
During operations, the SPHERES Tether Slosh interfaces with the SPHERES Facility in the applicable SPHERES ISS modules. Various test scenarios are envisioned which are all based on the following configuration: (1) two SPHERES pull the liquid filled SLOSH tank, which is connected to both SPHERES via a Kevlar tether. The liquid behavior inside the tank is monitored similar to the past tests carried out by NASA/Florida Institute of Technology (FIT); however, these use a tether and are not hard-mounted. Several experimental profiles are foreseen by maneuvering the slosh tank through the SPHERES working volume; (2) applying the same scenario as above, but utilizing a solid tank to investigate the difference of maneuvering a solid mass compared to a sloshing body.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

Information Pending

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Related Websites

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