View source for SPHERES

{{Short description|Free-flying robotic system}}
[[File:Three SPHERES on International Space Station.jpg|thumb|right|400px|SPHERES aboard ISS]]
The '''Synchronized Position Hold Engage and Reorient Experimental Satellite (SPHERES)''' are a series of [[miniaturized satellite]]s developed by [[Massachusetts Institute of Technology|MIT]]'s Space Systems Laboratory for [[NASA]] and US Military, to be used as a low-risk, extensible [[Testbed|test bed]] for the development of [[metrology]], formation flight, [[Space rendezvous|rendezvous]], docking and autonomy algorithms that are critical for future space missions that use distributed spacecraft architecture, such as [[Terrestrial Planet Finder]] and [[Orbital Express]].<ref name=":2" />
Each SPHERES satellite is an 18-sided [[polyhedron]], with a mass of about 4.1&nbsp;kg and a diameter of about 21&nbsp;cm. They can be used in the [[International Space Station]] as well as in ground-based laboratories, but not in the vacuum of [[Outer space|space]]. The battery-powered, self-contained units can operate semi-autonomously, using {{CO2}}-based cold-gas thrusters for movement and a series of ultrasonic beacons for orientation. The satellites can communicate with each other and with a control station wirelessly. The built-in features of the satellites can be extended using an expansion port.<ref name=":3" />
From 2006, three SPHERES units are being used in the International Space Station for a variety of experiments. The SPHERES Guest Scientist Program allow scientists to conduct new science experiments using SPHERES units, and the [[Zero Robotics|Zero Robotics Program]] allow students to participate in annual competitions that involve developing software to control SPHERES units.<ref name=":5">{{Cite web|title = The History of SPHERES|url = http://www.nasa.gov/spheres/the-history-of-spheres|website = NASA|accessdate = 2016-01-09|first = Simeon|last = Kanis| date=3 June 2015 }}</ref>
The SPHERES program is expected to continue until 2017, and possibly further.<ref name=":5" />{{Update inline|date=November 2021}}
The SPHERES project led to a newer project called [[Astrobee (ISS Autonomous Robot)|Astrobee]].<ref>{{Cite web|title = How NASA's Astrobee Robot Is Bringing Useful Autonomy to the ISS|url = https://spectrum.ieee.org/how-nasa-astrobee-robot-is-bringing-useful-autonomy-to-the-iss|website = IEEE SPECTRUM|date = 2017-02-09|access-date = 2018-03-13|first = Evan|last = Ackerman}}</ref>
== Development ==
[[File:Students test SPHERES on NASA KC-135 reduced gravity aircraft (JSC2000-E-09952).jpg|alt=MIT students test the SPHERES satellites aboard NASA's reduced gravity aircraft.|thumb|220x220px|MIT students test the SPHERES satellites aboard NASA's reduced gravity aircraft.]]
The initial development of SPHERES started in 1999, by a team of students at [[Massachusetts Institute of Technology]], as part of an [[aerospace engineering]] program. The concept of the satellite was conceived when Professor David Miller challenged the students to develop a device similar to the [[Technology in Star Wars|combat training remote]] seen in the 1977 movie ''[[Star Wars (film)|Star Wars Episode IV: A New Hope]]'' and more recently in ''[[Star Wars: Episode II – Attack of the Clones]]''. Several prototypes were developed during the course of the program, and were tested in ground laboratories as well as in parabolic flights using NASA's [[reduced gravity aircraft]].<ref name=":4" />
After the initial development, the SPHERES program was taken over by MIT's Space Systems Laboratory. In collaboration with [[Aurora Flight Sciences]], the design was refined and six flight-ready satellites were built, out of which three were delivered to the International Space Station.<ref name=":4" />
The SPHERES project is primarily funded by [[DARPA|Defense Advanced Research Projects Agency (DARPA)]].<ref name=":3" />
== Specifications ==
=== Structure and physical characteristics ===
[[File:SPHERES internal components.jpg|alt=A SPHERES satellite without the plastic shell. Aluminum structure, a control panel, ultrasonic sensors, thrusters, pressure regulator knob and pressure gauge are visible.|thumb|220x220px|A SPHERES satellite without the plastic shell. Aluminum structure, a control panel, ultrasonic sensors, thrusters, pressure regulator knob and pressure gauge are visible.]]
Each SPHERES satellite resembles an 18-sided [[polyhedron]], similar to a [[cuboctahedron]]. The aluminum structure of the satellite is enclosed in a semi-transparent plastic shell. The shell is red, blue, orange or black in color, to help with easy identification. The three satellites in the International Space Station are red, blue and orange. Each unit has a maximum diameter of 22.9&nbsp;cm and has a mass of 4.16&nbsp;kg including the consumables.<ref name=":4">{{Cite web|title = About SPHERES|url = http://ssl.mit.edu/spheres/about.html|website = ssl.mit.edu|accessdate = 2016-01-09|archive-date = 2016-03-05|archive-url = https://web.archive.org/web/20160305152655/http://ssl.mit.edu/spheres/about.html|url-status = dead}}</ref><ref name=":1">{{Cite web|url = http://ssl.mit.edu/spheres/library/SPHERES-Specifications.pdf|title = Spheres Fact Sheet|date = |accessdate = 1 January 2016|website = |publisher = |last = |first = |archive-date = 30 April 2016|archive-url = https://web.archive.org/web/20160430000245/http://ssl.mit.edu/spheres/library/SPHERES-Specifications.pdf|url-status = dead}}</ref>
=== Processing and communication ===
A Texas Instruments C6701 DSP running at 167&nbsp;MHz serves as the onboard computer. Flight software and experiment related instructions are written in [[C (programming language)|C programming language]].<ref name=":2">{{Cite web|url = http://ssl.mit.edu/spheres/resources/gsp/spheres-gsp.pdf|title = The SPHERES Guest Scientist Program|date = |accessdate = 9 January 2016|website = |publisher = |last = |first = |archive-date = 30 April 2016|archive-url = https://web.archive.org/web/20160430000251/http://ssl.mit.edu/spheres/resources/gsp/spheres-gsp.pdf|url-status = dead}}</ref>
The satellites can communicate with each other using a 916.5&nbsp;MHz, 16&nbsp;kbit/s radio link. Communication with the control station (a laptop computer) is done using an 868.35&nbsp;MHz, 16&nbsp;kbit/s radio link.<ref name=":1" /> SPHERES satellites are able to connect to the International Space Station's on-board Wi-Fi network for tasks that require a higher data bandwidth.<ref name=":3">{{Cite web|title = SPHERES FAQ|url = http://www.nasa.gov/spheres/spheres-faq|website = NASA|accessdate = 2016-01-09|first = Simeon|last = Kanis| date=3 June 2015 }}</ref>
=== Sensors and navigation ===
SPHERES satellites determine their position and attitude by using 23 on-board ultrasonic receivers (Murata MA40S4R) and 5 external ultrasonic reference beacons. The ultrasonic time-of-flight measurements from the external beacons to the on-board receivers are used to calculate the satellite's position with respect to the external reference frame.<ref name=":2" />
For rapid determination of position, the ultrasonic time-of-flight information is supplemented with the data from on-board [[accelerometer]]s (3x Honeywell QA-750 single-axis accelerometers) and [[gyroscope]]s (3x Systron Donner QRS14 single-axis rate gyroscopes).<ref name=":2" />
=== Power and actuation ===
SPHERES satellites are powered using two non-rechargeable 12v battery packs. Each battery pack consists of eight 1.5v [[AA battery]] cells that are spot-welded in series.<ref name=":3" />
The satellites are able to translate in the micro-gravity environment with [[Six degrees of freedom|6 degrees-of-freedom]], using twelve cold-gas thrusters that use liquid [[Carbon dioxide|{{CO2}}]] as propellant. The liquid {{CO2}} are stored in a small on-board container, similar to those that are used in [[paintball]] guns. The {{CO2}} is converted to a gaseous state before being ejected through the thrusters for propulsion. Desired thrust is achieved through pulse modulation of thrust solenoids.<ref name=":2" />
The maximum linear acceleration of the satellites is 0.17m/s2, with an accuracy of 0.5&nbsp;cm. The maximum angular acceleration is 3.5 rad/s2, with an accuracy of 2.5 degrees.<ref>{{Cite web|title = SPHERES Satellites|url = http://www.nasa.gov/spheres/spheres-satellites|website = NASA|accessdate = 2016-01-09|first = Simeon|last = Kanis| date=3 June 2015 }}</ref>
== Testing and support facilities ==
SPHERES program utilizes supporting facilities located at NASA's [[Ames Research Center|Ames Research Centre]].
=== 3 DoF Laboratory ===
[[File:SPHERES satellite on air carriages.jpg|alt=A SPHERES satellite is mounted on an air carriage at the 3 DoF laboratory. Visible are two liquid {{CO2}} containers used by the air carriage.|thumb|220x220px|A SPHERES satellite is mounted on an air carriage at the 3 DoF laboratory.]]
The 3 DoF laboratory facilitates simultaneous testing of up to three SPHERES satellites on a flat, nearly friction-less granite surface. The satellites are mounted on air carriages – stands that eject a stream of {{CO2}} to create a cushion of air – allowing the units to translate on X and Y axis, and rotate on Z axis.<ref name=":0">{{Cite web|title = SPHERES Facilities at NASA AMES|url = http://www.nasa.gov/spheres/spheres-facilities-at-nasa-ames|website = NASA|accessdate = 2016-01-09|first = Simeon|last = Kanis| date=3 June 2015 }}</ref>
=== MicroGravity Test Facility (MGTF) ===
The MicroGravity Test Facility (MGTF) facilitates testing of a single mobile SPHERES satellite, using six degrees-of-freedom. In this, the unit is held by a gimbal with 3 DoF, which is suspended from a translation crane with 3 DoF. The laboratory is able to provide a navigational reference frame in a similar configuration as in the International Space Station using five ultrasonic beacons, and the output of cold gas thrusters are analysed to simulate the expected movement in a micro-gravity environment.<ref name=":0"/><ref>{{Cite web|title = NASA - MicroGravity Test Facility|url = http://www.nasa.gov/centers/ames/research/technology-onepagers/microgravity_test_facility_prt.htm|website = www.nasa.gov|accessdate = 2016-01-09}}</ref>
=== Flight Assembly Laboratory ===
The Flight Assembly Laboratory is used to prepare and test consumables – battery packs and liquid {{CO2}} containers – used by the SPHERES units.
Individual cells of the battery packs are tested, spot-welded in series and tested again as a pack. The battery packs are discarded after use.
Spent {{CO2}} containers are returned to the Flight Assembly Laboratory for re-filling and safety testing before being flown back to the International Space Station.<ref name=":0"/>
==Delivery to the International Space Station==
The delivery of SPHERES satellites to the International Space Station were originally planned for 2003. However, due to the [[Space Shuttle Columbia disaster|loss of Space Shuttle Columbia]] in February 2003, the delivery did not take place until 2006.<ref name=":2" />
The first SPHERES unit was delivered to ISS by the unmanned resupply mission [[Progress M-56]] (ISS-21P) during April 2006. The second unit was delivered by the Space Shuttle mission [[STS-121]] in July 2006. The final unit was delivered by the Space Shuttle mission [[STS-116]] in December 2006.<ref>{{Cite web|url = https://www.nasa.gov/pdf/162182main_STS-116_Press_Kit.pdf|title = STS-116 Press Kit|date = |access-date = 13 January 2016|website = |publisher = |last = |first = }}</ref>
The SPHERES experiment aboard the International Space Station commenced on 18 May 2006.<ref name=":4" />
==Experiments==
=== SmartSPHERES ===
[[File:A smartphone-equipped SPHERES satellite.jpg|alt=A smartphone-equipped SPHERES satellite.|thumb|220x220px|A smartphone-equipped SPHERES satellite.]]
SmartSPHERES experiment equipped the three SPHERES satellite aboard the International Space Station with [[Nexus S]] [[smartphone]]s that were delivered via the Space Shuttle mission [[STS-135]]. Each satellite was enhanced through the use of processing power, wireless networking, camera, sensors and the touch sensitive display of the connected smartphone. The availability of the [[Android (operating system)|Android]] operating system's source code enabled the devices to be used as a compact, low-cost, low-power computers.<ref name=":6">{{Cite web|title = NASA's Smartphone-Powered Satellite|url = http://www.nasa.gov/mission_pages/station/main/spheres_smartphone.html|website = NASA|accessdate = 2016-01-10|first = NASA|last = Administrator| date=14 December 2015 }}</ref><ref>{{Cite web|title = Smart SPHERES Are About to Get A Whole Lot Smarter|url = https://www.nasa.gov/mission_pages/station/research/news/smart_spheres|website = NASA|accessdate = 2016-01-10|first = Kristine|last = Rainey| date=9 April 2015 }}</ref>
The experiment studies the use of SPHERES satellites to conduct autonomous and remotely operated environmental and inventory surveys aboard the Space Station, with the aim of reducing the astronaut's time spent on routine tasks. Knowledge gained will also help the development of future space vehicles that could perform [[Extravehicular activity|extravehicular activities]], and assist astronauts with their tasks.<ref name=":6" />
The SmartSPHERES experiment is managed by the [[Intelligent Robotics Group]] of the Ames Research Center with funding from Enabling Technology Development and Demonstration program of NASA's Exploration Systems Mission Directorate.<ref name=":6" />
=== SPHERES-VERTIGO ===
[[File:SPHERES-VERTIGO experiment on ISS (ISS034-E-056096).jpg|alt=A SPHERES satellite equipped with add-on VERTIGO goggles.|thumb|220x220px|A SPHERES satellite equipped with add-on VERTIGO goggles.]]
The SPHERES-VERTIGO (SPHERES-Visual Estimation and Relative Tracking for Inspection of Generic Objects) experiment aims to develop software and hardware that can generate three-dimensional maps of cooperative or non-cooperative objects using [[computer vision]], and navigate relative to such objects solely by reference to the generated maps.<ref name=":7">{{Cite web|title = NASA - Synchronized Position, Hold, Engage, Reorient, Experimental Satellites - VERTIGO|url = http://www.nasa.gov/mission_pages/station/research/experiments/869.html|website = www.nasa.gov|access-date = 2016-01-11}}</ref>
As part of the experiment, new [[Simultaneous localization and mapping|Simultaneous Localization and Mapping]] (SLAM) algorithms are developed and tested.<ref name=":7" />
To facilitate SPHERES-VERTIGO experiment, each SPHERES satellite aboard the ISS are equipped with an add-on "goggle" – a device connected to SPHERES using the expansion port, and carries a stereo camera, ultrasonic sensors, a single-board computer, high-speed communication facilities and batteries.<ref name=":7" />
Technologies developed will be used in future autonomous space vehicles that can operate alone or in groups to map [[asteroid]]s, inspect tumbling satellites or de-orbit [[space debris]].<ref name=":7" />
The experiment is part of the SPHERES Integrated Research Experiments (InSPIRE) program, funded by [[DARPA]].<ref name=":7" />
=== DOD SPHERES-RINGS ===
[[File:SPHERES-RINGS on ISS (ISS037-E-025868).jpg|alt=Two SPHERES satellites with the RINGS add-ons are being used in an experiment by NASA astronaut Michael Hopkins.|thumb|220x220px|Two SPHERES satellites with the RINGS add-ons are being used in an experiment by NASA astronaut Michael Hopkins.]]
DOD SPHERES-RINGS ([[United States Department of Defense|Department of Defense]] SPHERES-Resonant Inductive Near-field Generation System) experiment aims to develop software and hardware capable of [[Electromagnetic formation flight (EMFF)|Electromagnetic Formation Flight]] (EMFF) and wireless power transfer in microgravity environment.<ref name=":8">{{Cite web|title = NASA - Department of Defense Synchronized Position, Hold, Engage, Reorient, Experimental Satellites-RINGS|url = http://www.nasa.gov/mission_pages/station/research/experiments/916.html|website = www.nasa.gov|access-date = 2016-01-11}}</ref>
The experiment uses two hardware assemblies connected to SPHERES satellites, consisting of aluminum [[Resonance|resonant]] coils, coil housing with fans, electronics and batteries.<ref name=":8" />
Individual SPHERES units are maneuvered with respect to each other by generating controlled attractive, repulsive and shear forces using the electromagnetic coils. The same coils are used to wirelessly transfer power between SPHERES satellites through resonant [[inductive coupling]]. Software algorithms that avoid collision between satellites are also developed as part of the experiment.<ref name=":8" />
Knowledge gained through the experiment will help the development of propellant-free, plume-free clustered space vehicles, increase their operating lifetime, reduce spacecraft mass and associated operating risks.<ref name=":8" />
=== SPHERES-Slosh ===
Article: [[NASA_Launch_Services_Program#Slosh_fluid_dynamics_experiments|SPHERES-Slosh]]
=== SPHERES-Halo===
An expansion to the SPHERES satellites that forms a ring (halo) around the satellite to provide six expansion port attachment sites. Two were flown to the ISS.
=== SPHERES-Universal Docking Ports ===
Docking mechanism that enables two SPHERES satellites to attach rigidly together. Six were flown to the ISS.
== Use in education ==
=== Zero Robotics ===
{{Main|MIT Zero Robotics|l1=Zero Robotics}}
Zero Robotics is an annual international competition conducted by MIT, where participating student teams program the SPHERES satellites to solve a specific challenge. The competition is held under two tiers; the middle school tournament and the high school tournament.<ref name=":9">{{Cite web|title = What is Zero Robotics?|url = http://zerorobotics.mit.edu/what-is-zr/|website = zerorobotics.mit.edu|access-date = 2016-01-31}}</ref>
The initial rounds of the competition are conducted via simulations. The finalists' programs are loaded into SPHERES satellites aboard the International Space Station, and are executed by astronauts. The event is broadcast live to MIT, Europe and Australia.<ref name=":9" />
== See also ==
* [[AERCam Sprint]]
* [[Artificial intelligence]]
* [[Micro-g environment]]
* [[Robotics]]
* [[Electromagnetic Formation Flight]]
* [[Scientific research on the International Space Station]]
* [[Spherical robot]]
== References ==
{{Reflist}}
== External links ==
{{Commons category|SPHERES (satellite series)}}
* [http://www.nasa.gov/spheres SPHERES website] at NASA.gov
* [http://ssl.mit.edu/spheres/index.html SPHERES website] {{Webarchive|url=https://web.archive.org/web/20060815051652/http://ssl.mit.edu/spheres/index.html |date=2006-08-15 }} at MIT.edu
* [http://ssl.mit.edu/spheres/ISSdb/ts.php SPHERES Test Sessions] {{Webarchive|url=https://web.archive.org/web/20140203234045/http://ssl.mit.edu/spheres/ISSdb/ts.php |date=2014-02-03 }}
* [http://ssl.mit.edu/newsite/research/project.php?catagory=SPHERES SPHERES page] {{Webarchive|url=https://web.archive.org/web/20140126024734/http://ssl.mit.edu/newsite/research/project.php?catagory=SPHERES |date=2014-01-26 }} at MIT.edu
* [http://ssl.mit.edu/ MIT Space Systems Lab]
* [http://aurora.aero/ Aurora Flight Sciences]
* [https://www.theregister.co.uk/2010/04/20/iss_spheres_upgrades/ "Space Station lightsabre-sparring hoverdroids to be upgraded"] at ''[[The Register]]''
[[Category:International Space Station experiments]]
[[Category:Massachusetts Institute of Technology]]
[[Category:Space robots]]
[[Category:Small satellites]]
[[Category:Satellite series]]