Three SPHERES on International Space Station

The Synchronized Position Hold Engage and Reorient Experimental Satellite (SPHERES) are a series of

miniaturized satellite A small satellite, miniaturized satellite, or smallsat is a satellite of low mass and size, usually under . While all such satellites can be referred to as "small", different classifications are used to categorize them based on mass. Satellites ca ...

s developed by

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's Space Systems Laboratory for

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

and US Military, to be used as a low-risk, extensible test bed for the development of

metrology Metrology is the scientific study of measurement. It establishes a common understanding of units, crucial in linking human activities. Modern metrology has its roots in the French Revolution's political motivation to standardise units in Fran ...

, formation flight, rendezvous, docking and autonomy algorithms that are critical for future space missions that use distributed spacecraft architecture, such as

Terrestrial Planet Finder The Terrestrial Planet Finder (TPF) was a proposed project by NASA to construct a system of space telescopes for detecting extrasolar terrestrial planets. TPF was postponed several times and finally cancelled in 2011. There were two telescope ...

and

Orbital Express Orbital Express: ASTRO and NEXTSat Orbital Express was a space mission managed by the United States Defense Advanced Research Projects Agency (DARPA) and a team led by engineers at NASA's Marshall Space Flight Center (MSFC). The Orbital Express p ...

. Each SPHERES satellite is an 18-sided

polyhedron In geometry, a polyhedron (plural polyhedra or polyhedrons; ) is a three-dimensional shape with flat polygonal faces, straight edges and sharp corners or vertices. A convex polyhedron is the convex hull of finitely many points, not all on th ...

, with a mass of about 4.1 kg and a diameter of about 21 cm. They can be used in the

International Space Station The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...

as well as in ground-based laboratories, but not in the vacuum of

space Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually consider ...

. 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. 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 Program allow students to participate in annual competitions that involve developing software to control SPHERES units. The SPHERES program is expected to continue until 2017, and possibly further. The SPHERES project lead to a newer project called

Astrobee Astrobee is the designation of series of American sounding rockets with 1 - 3 stages. Aerojet-designed family of sounding rockets conceived as a lower-cost replacement of the liquid-propellant Aerobee. Several versions were realized: * The ...

Development

The initial development of SPHERES started in 1999, by a team of students at

Massachusetts Institute of Technology The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the ...

, as part of an

aerospace engineering Aerospace engineering is the primary field of engineering concerned with the development of aircraft and spacecraft. It has two major and overlapping branches: aeronautical engineering and astronautical engineering. Avionics engineering is si ...

program. The concept of the satellite was conceived when Professor David Miller challenged the students to develop a device similar to the combat training remote seen in the 1977 movie '' 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 A reduced-gravity aircraft is a type of fixed-wing aircraft that provides brief near-weightless environments for training astronauts, conducting research and making gravity-free movie shots. Versions of such airplanes were operated by the NAS ...

. After the initial development, the SPHERES program was taken over by MIT's Space Systems Laboratory. In collaboration with

Aurora Flight Sciences Aurora Flight Sciences is an American aviation and aeronautics research subsidiary of Boeing which primarily specializes in the design and construction of special-purpose Unmanned aerial vehicles. Aurora has been established for 20+ years and th ...

, the design was refined and six flight-ready satellites were built, out of which three were delivered to the International Space Station. The SPHERES project is primarily funded by Defense Advanced Research Projects Agency (DARPA).

Specifications

Structure and physical characteristics

Each SPHERES satellite resembles an 18-sided

. 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 cm and has a mass of 4.16 kg including the consumables.

Processing and communication

A Texas Instruments C6701 DSP running at 167 MHz serves as the onboard computer. Flight software and experiment related instructions are written in

C programming language ''The C Programming Language'' (sometimes termed ''K&R'', after its authors' initials) is a computer programming book written by Brian Kernighan and Dennis Ritchie, the latter of whom originally designed and implemented the language, as well as ...

. The satellites can communicate with each other using a 916.5 MHz, 16kbit/s radio link. Communication with the control station (a laptop computer) is done using an 868.35 MHz, 16kbit/s radio link. 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.

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. For rapid determination of position, the ultrasonic time-of-flight information is supplemented with the data from on-board

accelerometer An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is accele ...

s (3x Honeywell QA-750 single-axis accelerometers) and

gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rota ...

s (3x Systron Donner QRS14 single-axis rate gyroscopes).

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. The satellites are able to translate in the micro-gravity environment with 6 degrees-of-freedom, using twelve cold-gas thrusters that use liquid

CO2 Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

as propellant. The liquid CO2 are stored in a small on-board container, similar to those that are used in

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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. The maximum linear acceleration of the satellites is 0.17m/s2, with an accuracy of 0.5 cm. The maximum angular acceleration is 3.5 rad/s2, with an accuracy of 2.5 degrees.

Testing and support facilities

SPHERES program utilizes supporting facilities located at NASA's Ames Research Centre.

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.

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.

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.

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 loss of Space Shuttle Columbia in February 2003, the delivery did not take place until 2006. 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 STS-121 was a 2006 NASA Space Shuttle mission to the International Space Station (ISS) flown by . The main purposes of the mission were to test new safety and repair techniques introduced following the ''Columbia'' disaster of February 2003 as w ...

in July 2006. The final unit was delivered by the Space Shuttle mission

STS-116 STS-116 was a Space Shuttle mission to the International Space Station (ISS) flown by Space Shuttle '' Discovery''. ''Discovery'' lifted off on 9 December 2006 at 20:47:35 EST. A previous launch attempt on 7 December had been canceled due to cl ...

in December 2006. The SPHERES experiment aboard the International Space Station commenced on 18 May 2006.

Experiments

SmartSPHERES

SmartSPHERES experiment equipped the three SPHERES satellite aboard the International Space Station with

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s that were delivered via the Space Shuttle mission

STS-135 STS-135 ( ISS assembly flight ULF7) was the 135th and final mission of the American Space Shuttle program. It used the orbiter ''Atlantis'' and hardware originally processed for the STS-335 contingency mission, which was not flown. STS-135 la ...

. 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's source code enabled the devices to be used as a compact, low-cost, low-power computers. 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 activities Extravehicular activity (EVA) is any activity done by an astronaut in outer space outside a spacecraft. In the absence of a breathable Earthlike atmosphere, the astronaut is completely reliant on a space suit for environmental support. EVA inc ...

, and assist astronauts with their tasks. The SmartSPHERES experiment is managed by the

Intelligent Robotics Group Intelligent Robotics Group (IRG) is a division of the Ames Research Center at Moffett Federal Airfield in California's Silicon Valley. Description The 2009 Director of the Intelligent Robotics Group Terry Fong stated in an interview that See ...

of the Ames Research Center with funding from Enabling Technology Development and Demonstration program of NASA's Exploration Systems Mission Directorate.

SPHERES-VERTIGO

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 Computer vision is an interdisciplinary scientific field that deals with how computers can gain high-level understanding from digital images or videos. From the perspective of engineering, it seeks to understand and automate tasks that the hum ...

, and navigate relative to such objects solely by reference to the generated maps. As part of the experiment, new

Simultaneous Localization and Mapping Simultaneous localization and mapping (SLAM) is the computational problem of constructing or updating a map of an unknown environment while simultaneously keeping track of an agent's location within it. While this initially appears to be a chick ...

(SLAM) algorithms are developed and tested. 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. Technologies developed will be used in future autonomous space vehicles that can operate alone or in groups to map

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s, inspect tumbling satellites or de-orbit

space debris Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) are defunct human-made objects in space—principally in Earth orbit—which no longer serve a useful function. These include derelict spacecr ...

. The experiment is part of the SPHERES Integrated Research Experiments (InSPIRE) program, funded by

DARPA The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Adv ...

DOD SPHERES-RINGS

DOD SPHERES-RINGS (

Department of Defense Department of Defence or Department of Defense may refer to: Current departments of defence * Department of Defence (Australia) * Department of National Defence (Canada) * Department of Defence (Ireland) * Department of National Defense (Philippin ...

SPHERES-Resonant Inductive Near-field Generation System) experiment aims to develop software and hardware capable of Electromagnetic Formation Flight (EMFF) and wireless power transfer in microgravity environment. The experiment uses two hardware assemblies connected to SPHERES satellites, consisting of aluminum

resonant Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...

coils, coil housing with fans, electronics and batteries. 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 In electrical engineering, two conductors are said to be inductively coupled or magnetically coupled when they are configured in a way such that change in current through one wire induces a voltage across the ends of the other wire through el ...

. Software algorithms that avoid collision between satellites are also developed as part of the experiment. 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.

SPHERES-Slosh

Article: SPHERES-Slosh

Use in education

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. 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.

References

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