Synchronized Position Hold, Engage, Reorient, Experimental Satellites


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Facility Summary

This content was provided by Andres Martinez, and is maintained in a database by the ISS Program Science Office.

Brief Summary

Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) are bowling-ball sized satellites that provide a test bed for development and research into multi-body formation flying, multi-spacecraft control algorithms, and free-flying physical and material science investigations. Up to three self-contained free-flying satellites can fly within the cabin of the International Space Station (ISS), performing flight formations, testing of control algorithms or as a platform for investigations requiring this unique free-flying test environment. Each satellite is a self-contained unit with power, propulsion, computers, navigation equipment, and provides physical and electrical connections (via standardized expansion ports) for PI provided hardware and sensors.

Facility Manager(s)

  • Andres Martinez, Ames Research Center, Mottett Field, CA, United States
  • Facility Representative(s)

    Information Pending


    NASA Ames Research Center, Moffett Field, CA, United States

    Sponsoring Space Agency

    National Aeronautics and Space Administration (NASA)

    Sponsoring Organization

    Human Exploration and Operations Mission Directorate (HEOMD)

    ISS Expedition Duration

    September 2010 - March 2014

    Expeditions Assigned


    Previous ISS Missions

    SPHERES on the ISS began during Expedition 8 and testing with one satellite was performed early during Expedition 13. The second satellite was delivered to ISS on STS-121 which allowed testing of the two satellite configuration beginning in August 2006. The third satellite was delivered on STS-116, and the three satellite configuration testing began during ISS Expedition 14.
    Investigations either completed or in work for this facility include:


    • SPHERES-Slosh


    • SPHERES-Zero-Robotics

    • SPHERES-Smartphone


    • SPHERES-Interact



  • Onboard
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    Facility Overview

    • SPHERES consists of three self-contained, free flying satellites for use inside the ISS.

    • SPHERES can test algorithms related to relative attitude control and station-keeping between satellites, re-targeting and image plane filling maneuvers, collision avoidance and fuel balancing algorithms, as well as an array of geometry estimators used in various missions.

    • The SPHERES facility acts as a free-flying platform that is capable of accommodating varying mounting features and mechanisms in order to test and examine the physical or mechanical properties of materials in microgravity.

    • Individual satellites communicate with each other and an ISS laptop through a low-power 900 MHz wireless link.
    SPHERES provides a platform for conducting physical sciences investigations (e.g., liquid behavior studies), free-flying spatial analysis (e.g., visual inspection/navigation), multi-body formation flying and various multi-spacecraft control algorithm model verification and analysis. This facility consists of three self-contained satellites (i.e., SPHERES). Each satellite is an 18-sided polyhedron that is 0.2 meter in diameter and weighs 3.5 kilograms. Individual satellites contain an internal propulsion system, power, avionics, software, communications, and metrology subsystems. The propulsion system uses carbon dioxide (CO2), which is expelled through the cold gas thrusters. SPHERES satellites are powered by AA batteries. The metrology subsystem provides real-time position and attitude information. To simulate ground station-keeping, a laptop is used to transmit navigational data and formation flying algorithms. Once data is uploaded, the satellites will perform autonomously and hold the formation until a new command is given. Thus acting as a test-bed for formation flying by satellites and testing the theories and calculations that coordinate the motion of multiple bodies maneuvering in microgravity.

    Sessions are nominally about four hours long and they consist of three main phases: Setup, Run Tests, and shutdown. Setup takes approximately 1.5 hours and prepares the facility for the test session by deploying beacons within a module, adding tanks and batteries to the satellites and configuring the SSC computer with an antenna and the SPHERES GUI (software). Once the equipment is setup, it is ready to run tests. We typically allow approximately two hours for running tests. The tests for each session are defined ahead of time with a detailed test plan. SPHERES data generated during the tests is stored real-time on the SSC T:\ drive. The ground can access the data and return it to any team or group using SPHERES within a few days. At the conclusion of the day's tests, it requires approximately 30 minutes for the crew to deconfigure and stow the equipment.

    Should the satellites run out of CO2 or batteries during a test session, those items can be replaced real time.

    SPHERES is only allowed in the USOS, and is currently operating in the JEM, bays 4 and 5. Operations are not permitted in the Russian segment due to concerns with infrared interference. Position information is known by setting up a series of five beacons in the work area which the satellites use to perform ranging via ultrasound and infrared pulses.

    SPHERES provides a test bed for many space applications. From a fundamental level, the SPHERES provides testing and validation of spacecraft control, multi-spacecraft coordinated flight and free flying spatial analysis inside the relatively benign, yet microgravity environment of the ISS. Successful algorithms from these experiments can be directly applied to tasks such as cooperative and non-cooperative docking, non-destructive inspection, and precision flight planning. All of these algorithms are vital for safe and reliable operation of future SPHERES designs inside and outside of the host spacecraft such as the ISS.

    SPHERES also allows us to explore higher level applications such as autonomous free-flying robotics and remote telepresence. These applications require high levels of sensing, localization, mapping, planning, and execution. Advancements in these areas will enable future crewmembers to focus their efforts on science and less on monitoring and spacecraft maintenance. Much like robot vacuum cleaners and lawn mowers are helping humans on the earth, one can easily imagine spacecraft where a host of free-flying robots help crewmembers achieve successful missions in space.

    Finally SPHERES provides a test platform for physical and material science investigations requiring this unique free-flying test environment.

    Lessons learned from SPHERES experiments in orbit can be applied to many Earth applications. The control algorithms for free-flying objects in space can be adapted to terrestrial free flyer platforms like unmanned air vehicles (UAVs) and autonomous underwater vehicles (AUVs). In the case of air vehicles, quadcopter aircraft designs have demonstrated movement through their environment much like the SPHERES moves on the ISS. Many of the robotics sensing, mapping, and planning algorithms can be adapted to such aircraft. Underwater remotely operated vehicles are regularly used for inspection and docking tasks in the extreme depths of our ocean. Experimental results and lessons learned from SPHERES on the ISS can help inform how AUV operators can better complete their difficult underwater tasks from remote and safe locations on the surface.


    Facility Operations

    Information Pending

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    Results/More Information

    Results Publications

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    Ground Based Results Publications

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    ISS Patents

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    Related Publications

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    Related Websites

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    image NASA Image: ISS16E014220SPHERES Satellites flying in formation
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    image NASA Image: ISS017E015131 - Astronaut Greg Chamitoff posing with SPHERES during a test run - Expedition 17and 18.
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    image ISS Commander Scott Kelly ?juggles? the SPHERES satellites during a test session during Increment 25.
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    image Astronaut Mike Fossum executes the first SPHERES Test Session with the Smartphone during Increment 29. Image courtesy of NASA.
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    image SPHERES Satellite with Expansion Port, capable of supporting additional hardware.Image courtesy of NASA.
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    image NASA Image: ISS018E005212 - Astronaut Greg Chamitoff programming a SPHERES test run during Expedition 17and 18.
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