SPHERES Tether Demo (SPHERES Tether Demo) - 11.22.16

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

ISS Science for Everyone

Science Objectives for Everyone
Space debris can collide with other orbiting objects and endanger satellites or manned spacecraft. Catching and removing debris eliminates this threat, but capturing material in orbit poses many technical challenges. The Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) Tether Demo studies the dynamics of a tethered capture object and a “space tug” chase vehicle, improving computer programs needed for removing space debris as well as capturing scientific samples from other planets.
Science Results for Everyone
Information Pending

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

OpNom: SPHERES Tether Demo

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

Information Pending

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
Scientific Discovery

ISS Expedition Duration
September 2015 - March 2016; September 2016 - February 2017

Expeditions Assigned

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • SPHERES Tether Demo tests methodologies and strategies to de-tumble and stabilize the complete system for target removal are to be tested using different algorithms programmed into the SPHERES spacecraft GNC.
  • The results are to be used to feed computer models of the complete system to calibrate/confirm the computer model, which could then be scaled to larger flight-sized systems, with the potential to repeat these tests again with the lessons learned.
  • The demonstration enables further understanding of the tethering system dynamics, which has yet to be studied in detail, for the development of a net capture system. This allows the potential for the development of control mechanisms for captured items, and raising the overall technical readiness level of the net capture system.


A series of tests are performed with the combined Chaser-Tether-Target System with the following variables:
  • Variation in tether tension/slack between the chase vehicle and the capture target.
  • Variation in chase vehicle and capture target velocities.
  • Variation in tether alignment between the chase vehicle and the capture target.
  • Potentially the variation of Target initial characteristics, e.g. attitude, tumbling rates.
  • Development of control algorithms and adoption of different control strategies to stabilize target for accurate removal.

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Space Applications
Before humans travel to Mars and other distant destinations, scientists plan to use robots to collect samples from planetary surfaces and return them to Earth. This investigation improves the research and development for a capture system that can retrieve these samples. The investigation also supports development of an emergency capture system for use during spacewalks, collecting lost tool kits or other stray items. Results from SPHERES Tether Demo can also improve efforts to design systems that can capture and repair satellites in the crowded sun-synchronous and geosynchronous orbit ranges.

Earth Applications
Satellites that break down or reach the end of their lives become space junk, but a capture and tether system could allow satellites to be repaired instead of replaced, lowering costs for telecommunications companies and many other users on Earth. Results from this investigation could also improve efforts to capture a near-Earth asteroid for detailed study, engaging the public in scientific exploration.

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Operational Requirements and Protocols

The scientific observations are carried out by means of 2 SPHERES satellites which are interconnected by a tether at about 18” distance apart. One SPHERES acts as the Chaser, while the other represents the Target. Two different tether materials are used: Monofilament Nylon and Kevlar, which provide different elasticity, and thereby different responses during towing process. For each tether, four baseline runs are performed under varying configurations, as well as several back-up runs as crew time permits. Experiment runs are performed sequentially, if required, providing some spacing to avoid freezing of the SPHERES jets.
Privatized High Definition (HD) video is recorded for the actual experiment runs; however, set-up and overall scenery is available as public video. In addition, positional and acceleration data from both SPHERES is to be made available for off-line investigation. No return of samples is planned.

Six hours have been requested for a full day of SPHERES Tether Demo, attended by 2 crew:
Hours 0 – 2 involves crew orientation, a big picture of the goals, and a procedure walk through. This is followed by the un-stow and set-up of 2 SPHERES, a check of fuelling, battery status, initiation of ground link, and installation of Tether Demo to both SPHERES.
Hours 2 – 5 involve 4 Tether Demo runs with monofilament Nylon tether in different configurations. 30 minutes are required for tether assembly exchange from monofilament to Kevlar Assy. 4 Tether Demo runs are done with Kevlar tether in different configurations. Back-up runs can be accomplished, if crew time permits.
Hours 5 – 6 involve removal and stow of Tether Demo hardware from SPHERES, followed by the deactivation and stow of SPHERES.

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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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A rendering of the SPHERES satellite with Tether Demo attachment.

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