Minimize ISS Utilization: SPHERES

ISS Utilization: SPHERES (Synchronized Position Hold Engage Re-orient Experiment Satellites)

SPHERES is an experimental testbed to demonstrate the dynamics of formation flight (FF) in satellite systems. The program was developed and installed at the SSL (Space Systems Laboratory) of MIT (Massachusetts Institute of Technology) to provide the USAF (United States Air Force) and NASA with long-term, replenishable, and upgradable test capabilities for the validation of high risk metrology, control, and autonomy technologies. DARPA (Defense Advanced Research Projects Agency) is a major sponsor of the SPHERES program which started in the late 1990s. 1) 2) 3) 4) 5) 6)


Figure 1: Illustration of a SPHERES three nanosatellites (image credit: MIT/SSL)

The nanosatellites were originally designed by MIT students (under a program funded by MIT, DARPA and NASA), and built by Payload Systems Inc. of Cambridge, MA. The first operational prototype was completed in the winter 2000 and tested in the laboratory. Two additional units were fabricated in the spring of 2000. Initial flight test experiments, evaluating both testbed and control algorithm performance, were conducted (in 2000, 2001 and 2003) onboard NASA's KC-135 aircraft (three flight campaigns). The idea of SPHERES system testing and research on ISS (with its sustained zero-g environment) for a broader spectrum of applications was a natural consequence after the successful flight campaign demonstrations. 7) 8) 9) 10) 11) 12)

The overall objectives include the demonstration of the following functions: Autonomous rendezvous, docking, and reconfiguration” algorithms, testing of relative attitude control and station-keeping between satellites, re-targeting and image plane filling maneuvers, collision avoidance and fuel balancing algorithms, and an array of geometry estimators used in various missions. A main goal of SPHERES is to support research in distributed aperture control for such applications as telescope arrays - by substituting several smaller, separated mirrors for one large mirror. The SPHERES program technologies are critical to the operation of distributed satellite and docking missions such as TPF (Terrestrial Planet Finder) of NASA and OE (Orbital Express) of DoD.


Figure 2: Illustration of the structure of the SPHERES nanosatellite (image credit: MIT/SSL)

SPHERES nanosatellites:

The SPHERES satellites are self-contained with on-board propulsion, processing, RF communication, and metrology. In addition, the testbed has four metrology transmitters that provide global metrology reference and a laptop computer that acts as a “ground station” and provides experiment control.

All SPHERES satellites are identical in structure and internal composition. The SPHERES satellite design is modular. The design of the individual subsystems can be easily integrated into another project which use different configurations due to their simple interfaces and operational independence. The modularity enables a wide spectrum of flexibility in the use of the facility. The SPHERES system consists of the following basic elements: 13) 14)

• Three experimental self-contained 20 cm diameter free-floating nanosatellites (each with a dry mass of 3.55 kg, wet mass of 4.16 kg) which perform the various algorithms. The self-contained nanosatellites that are 18-sided polyhedrons.

• Five small ultrasound beacon devices are located in the SPHERES work envelope, they are acting as the navigation system (metrology beacon system). The ultrasound transmitter beacons measure their respective positions and attitudes in relation to one other and to the defined volume. Each beacon is self-contained and uses two standard Duracell Ultra AA batteries.

• The nanosatellites communicate with each other and an ISS laptop through a low-power wireless (RF) link.

Each of the nanosatellites contains an internal cold gas propulsion system, power, avionics, software, communications and metrology subsystems. The propulsion system uses carbon dioxide (CO2) which is expelled through thrusters. The SPHERES nanosatellites are powered by AA batteries. The metrology subsystem provides real-time position and attitude information. To simulate ground station keeping, a laptop is being used to transmit navigational data, and formation flight algorithms.


22 cm

Dry mass, wet mass

3.55 kg, 4.3 kg (with tank and batteries)


0.2 N

Power, battery lifetime

13 W, 2 hours (replaceable)

Linear acceleration, angular acceleration

0.17 m/s2 (max), 3.5 rad/s2 (max)

CO2, internal pressure level

170 gram, 59 - 3.45 bar (high & low pressure of storage tank)

RF communications (UHF band)

916.5 MHz (± 1MHz), 868.35 MHz (± 1MHz)

Table 1: Overview of SPHERES satellite parameters


Figure 3: Overview of the propulsion subsystem (image credit: MIT/SSL)


Figure 4: Various subsystem locations of SPHERES (image credit: MIT/SSL, Payload Systems Inc.)


Figure 5: Alternate view of a covered SPHERES satellite (image credit: MIT/SSL)

PADS (Position and Attitude Determination System). The objective of PADS is to provide real-time position and attitude information to each nanosatellite. PADS consists of: 15) 16)

• Ultrasonic beacons attached to the work envelope “walls” and ultrasonic receivers located onboard each nanosatellite (the beacon locations define the operational volume or the outer perimeter of the work envelope). The ultrasonic beacons provide low-rate (1-2 Hz) satellite position and attitude information relative to the work envelope.

• IMUs (Inertial Measurement Units) consisting of accelerometers and rate gyroscopes located on board each nanosatellite.


Accelerometers (Q-Flex 750)

Gyroscopes (BEI Gyrochip II)

Measurement range

±25.6 mg



12.5 µg/count

0.0407º s-1 count-1


300 Hz

300 Hz


< 7 µg rms (for 0 to 10 Hz)
< 70 µg rms (for 10 to 500 Hz)

0.05º/s (Hz)1/2 (for 0 to 100 Hz)

Table 2: Performance parameters of the accelerometers and gyroscopes

Time-of-flight ranging (operational scenario):

- “Master” satellite requests a global reading by emitting an IR flash

- Satellites turn off thrusters to listen for the ultrasonic pulses

- Beacons respond to IR flash with ultrasonic pulses

- Receivers on the satellite record the times when the ultrasonic pulses are received

- Satellites compute ranges based on the time of flight of the pulse

- Satellites calculate position and attitude from ranges.


Figure 6: Schematic of ultrasound device positioning for work envelope definition (image credit: MIT/SSL)


Figure 7: Block diagram of PADS (image credit: MIT/SSL, Payload Systems Inc.)


Figure 8: A hierarchical view of the GN&C architecture used on the SPHERES testbed 17) 18)



SPHERES on ISS (International Space Station):

The SPHERES payload was scheduled to fly on Shuttle flight (STS-114) in July 2003 to be installed on ISS (International Space Station). However, SPHERES experienced several times long delays due to the loss of Shuttle Columbia (STS-107) and its crew of 7 astronauts on Feb. 1, 2003. The accident resulted into the largest investigation ever by NASA. As a consequence of the investigation, the ISS build-up phase came to a complete halt. The very next Shuttle flight (STS-114) took place on July 26, 2005, ending 2 1/2 years of Shuttle grounding.

The first sphere of three of the SPHERES payload was taken to the US Laboratory (Unity) of the ISS on April 24, 2006. The ISS service flight was provided by a Soyuz-U launch vehicle with the Progress M-56 payload from Baikonur, Kazakhstan. Two additional spheres of SPHERES are scheduled to reach the space station, as payloads of a Shuttle mission, by the end of 2006. The micro-gravity environment of the ISS allows for maneuvers in 6 DoF (Degree of Freedom). The allocated test space (work envelope) in the US Lab has dimensions of about 1.5 m x 1.5 m x 2.m. 19) 20)

The ISS testbed provides a risk-tolerant environment capable of testing unknown algorithms and recovering from failures at low costs compared to that of a full mission. The program provides near-real-time human control and observability for guest scientists in a ground station, and in addition a manipulation capability by operators in the ISS.

The SPHERES testbed consists of two parts; a ground testbed located at MIT/SSL, and a flight testbed in the ISS that is being operated by astronauts as an interactive laboratory. The ISS provides unique opportunities for:

- Supervised and interactive experimentation

- Immediate assessment of test results

- Space research in a risk-tolerant environment

- Experimentation in three dimensional microgravity dynamics.

The SPHERES elements on ISS can maneuver in six degrees of freedom, communicate with each other and with the laptop control station, and determine their positions, velocities, attitudes, and angular rates with respect to an ISS-fixed or labfixed reference frame. 21)

Maneuvers are performed using a cold-gas propulsion system. Each thruster assembly consists of a solenoid-actuated valve with a micro-machined nozzle. Twelve thruster assemblies are positioned in pairs to provide complete attitude and position control. The propellant is stored in removable tanks. Each tank is expected to provide approximately 30 minutes of active operation in microgravity under normal operation on the ISS.

The SPHERES program on the ISS is led by MIT/SSL and Aurora Flight Sciences, and supported by the DoD/DARPA (Defense Advanced Research Projects Agency) and STP (Space Test Program) as well as by NASA.


Figure 9: CAD rendering of SPHERES (image credit: MIT/SSL)

Each sphere features an onboard DSP (Digital Signal Processor) of Texas Instruments (model C6701) providing ample computational power and flexibility (up to 167 MFLOPS with un-optimized code, and up to 1.0 GFLOPS with fully-optimized code). The flight software is stored in FLASH memory, and may be up to 224 kB in size.

Two packs of AA batteries provide power for each sphere. A set of batteries provides power for two hours of typical operation.

RF communications: Each satellite is equipped with two low-power transceivers for inter-satellite communication and satellite-to-laptop communication. The spheres communicate on two separate radio channels. Each channel has an effective capacity of about 22 kByte/s. One channel is dedicated to sphere-to-sphere (STS) communications, the other channel is used for sphere-to-laptop (STL) communications. The STS channel is typically being used for user-defined algorithm coordination, while the STL channel handles telemetry downlink and command uplink. Both channels are bi-directional; however, the communication hardware is half-duplex, meaning that only one station on each channel can transmit at a time.


Figure 10: Operational concept for the SPHERES testbed in the ISS (image credit: The Boeing Company)

Launch of next SPHERES payloads:

• The second satellite arrived on STS-121 flight of Discovery, July 4-17, 2006 (13 day mission). The arrival allowed testing of a “two satellite configuration” which started in August 2006.

• The third one arrived on flight STS-116, Discovery, Dec. 10-22, 2006 (13 day mission).

Hence, experimentation with the complete SPHERES system configuration commenced inside the ISS in 2007.

SPHERES test sessions aboard the ISS:

Five test sessions were conducted aboard the ISS during 2006: May 18, May 20, August 12, August 19, and November 11. A test session with the first single sphere took place on May 18, 2006 - floating inside the ISS and being watched by the astronauts. The first test flight consisted of a series of 10 to 15 pre-planned maneuvers, each lasting up to 10 minutes. 22)

The first four sessions helped the SPHERES team achieve steady-state operations, having fully understood the microgravity capabilities and behavior of the facilities and the ISS. Using the data collected from each test session, the SPHERES team incrementally matured formation flight and docking algorithms resulting in multiple “space firsts.” On the second test session it was the first space program to intentionally simulate failures of thrusters in space in order to test fault detection algorithms. During the fifth session SPHERES was the first to demonstrate docking to a tumbling target in a microgravity environment. The circular formation flight was another first (demonstrate covering an optical field in a microgravity environment with separated spacecraft), although there were synchronization problems that prevented the test from being fully successful, so it requires further research. - SPHERES is expected to operate aboard the station for multiple years to complete these tasks and more.




- Hardware checkout
- Open-loop control, 3DoF closed-loop rotations, and basic maneuvers towards docking


- Firmware fix (from session 1)
- 3DoF closed loop rotations; fault detection and isolation (FDI) of simulated thruster failures; position hold, and autonomous docking translation maneuvers


- Autonomous docking to a fixed beacon
- On-line calculation of the mass and inertia of the satellite (mass-ID)
- Two satellite initial tests: formation flight (3DoF slave/master) and docking


- Global metrology system checkout
- Show “avoidance” trajectories
- Two satellite formation flight: 6DoF slave/master
- Initial tests of two satellites docking


- Continue tests for mass-ID
- Cooperative and uncooperative docking and “safe docking”
- Peer-to-peer formation flight maneuver

Table 3: Overview of test sessions on ISS in 2006


Figure 11: SPHERES hardware components operating aboard the ISS (image credit: NASA, MIT)


Figure 12: SPHERES experiment of two units in the ISS module Destiny as seen by astronaut Thomas Reiter (image credit: NASA)


Figure 13: Three satellites fly in formation on ISS as part of the SPHERES investigation (image credit: NASA)


GSP (Guest Scientist Program):

The SPHERES GSP provides a common framework for collaboration, and facilitates access to the SPHERES laboratory (distributed architecture). It is designed to support parallel use of the testbed by researchers with diverse research interests and goals. Specifically, the GSP enables geographically distributed researchers to implement and test algorithms, obtain experiment data, iterate on algorithm design, and otherwise participate fully in the ground and flight laboratories on time scales of days and weeks rather than years. 23)

In 2006, the GSP started already; the first test sessions had participants from a different group within MIT and with NASA Ames.

Prior to sending SPHERES algorithms to the ISS, the scientists conduct tests on the SPHERES flat table testbed in the MIT SSL laboratory. The flat table testbed uses the same flight hardware that is onboard the ISS, but the SPHERES are mounted on air carriages to float on it.


The reconfiguration maneuver problem for multiple spacecraft in deep space environment:

There are two key types of trajectory design problems for formation flying spacecraft: 24)

1) Reconfiguration, which consists of maneuvering a fleet of spacecraft from one formation to another

2) Station-keeping, which consists of keeping a cluster of fleet of spacecraft in a specific formation for a determined part of the trajectory.

Both types of formation flying maneuvers must be addressed for deep-space missions where the relative spacecraft dynamics usually reduces to double integrators, or planetary orbital environment flying missions where spacecraft are subjected to significant orbital dynamics and environmental disturbances.

The SPHERES experiments were designed using two different two-stage path planning algorithms previously developed to solve the general multispacecraft translation and rotation reconfiguration maneuver problem with coupled constraints. This problem is particularly difficult because of the nonlinearity of the attitude dynamics, the non-convexity of some of the constraints, and the coupling between the positions and attitudes of all spacecraft. 25)

In March and April 2007, some reconfiguration experiments were performed with SPHERES on ISS which allowed to test the reconfiguration maneuver algorithms in real microgravity environment. - The ISS experiments achieved their main goal: the application of the two-stage reconfiguration maneuvers design to real satellites in a microgravity environment, thus validating the algorithms used to design them.


ZERO-Robotics program:

In 2009, MIT started the ZERO-Robotics program which provides high school students the opportunity to develop algorithms for SPHERES on board the ISS. Students work on the design of software to accomplish complex tasks in space; such as docking, assembly, and formation flight. As for the competition, each team must complete a set of pre-determined tasks, whereby they are measured for performance. During all phases, the students will be challenged not only with programming, but also with the development of documentation and presentations to add to their engineering and communication skills. In all cases, the students will have to learn and practice successful teamwork skills as there will be minimum team size requirements. 26)

There are four steps in the competition:

1) Proposal submission: Students propose a solution to the challenge of the competition. Students should clearly outline the motivation, the science behind their algorithm, how they will implement it, and data they expect to collect to show it worked properly. This phase is intended to teach students the basics of writing a proposal. This step also serves as a registration step. Teams are not eliminated at this step.

2) Simulation: Students implement their algorithm in simulation. This step verifies successful algorithm implementation, prior to hardware testing, and allows for a baseline performance expectation. If the number of teams participating is greater than can be accommodated in flight, this step can be used as an elimination round.

3) Ground Testing: Teams translate their algorithms from simulation to hardware, accounting for computation and communication limitations. Teams that demonstrate correctly operating simulations are invited to MIT's flat floor facility in Cambridge, MA to test them. Teams are selected based on the performance of hardware tests.

4) Flight Testing: The selected teams will modify their algorithms for implementation in space. Tests are integrated and packaged to be run on ISS. This step includes at least one ISS test session, with live feed of the crew executing the tests. Students will have the opportunity to view their test run in real-time. Data and telemetry will be downlinked to the students a few days after the event so that they can perform data analysis and submit a final report.

ZERO-Robotics is envisioned as a robotics competition that opens the world-class research facilities on the ISS to hundreds (potentially thousands) of students at multiple educational levels. A key objective is to inspire future scientists and engineers by making the benefits and resources of the space program tangible to the students. In this way, students will view working in space as reachable objective that is not just reserved for astronauts, and will grow up pushing the limits of space exploration, engineering, and development. Further, ZERO-Robotics helps build critical engineering skills for students, such as problem solving, design thought process, operations training, team work, and presentation skills.

The goal of the ISS as a National Laboratory is to educate them at a deeper level that keeps students interested in science, technology, engineering, and mathematics (STEM).

Pilot program: A pilot Zero-Robotics program was started in the fall of 2009 with students from two High Schools in Idaho. The pilot program did not require the teams to create proposals, and there was no “elimination” rounds. However, they did compete against each other in simulation, on the flat floor, and aboard the ISS. In mid-December 2009, the teams of the 2 schools successfully executed their SPHERES control software on the station (assistance from MIT).

National program: The conclusion of the pilot program marks the start of the preparations for the first year (2010) of a national program. Several organizations form part of the ZERO-Robotics efforts: MIT SSL, Aurora Flight Sciences, the Space Grant Program, DARPA, and NASA (Ref. 26).

- The MIT SPHERES team leads the academic and software development efforts (tutorials, simulations, competition scenarios, etc).

- Aurora Flight Sciences ensures the continued operation of SPHERES aboard the ISS by manufacturing and providing SPHERES supplies.

- The Space Grant program has been approached to become the general administration and to provide public relations and human resources.

- The NASA Education Office is expected to have at least one person be a full time liaison to the program, working with crews and public relations teams.

- DARPA, the original sponsor of SPHERES, will participate by providing further public relations and being a source of ideas for the competitions; there is the potential of DoD sponsored scholarships for participants/winners.



VERTIGO (Visual Estimation for Relative Tracking and Inspection of Generic Objects)

In 2008, the MIT/SSL ( Space Systems Laboratory) began a program to develop an upgrade to the SPHERES satellites that would allow it to perform vision based navigation experiments onboard the ISS. This was the LIIVe (Low Impact Inspection Vehicle) program that was sponsored by the Office of Naval Research and NRL (Naval Research Laboratory). This program’s intent was to develop a high-fidelity prototype of the hardware that could be launched to the ISS under a future program. This program resulted in the design and fabrication of the LIIVe Goggles, shown in Figure 14. 27) 28) 29) 30)


Figure 14: Photo of the LIIVe Goggles (image credit: MIT)

The LIIVe Goggles add two grayscale cameras (in either stereo or right angle configurations), a 1.0 GHz Via C7 x 86 microprocessor, a 16 GB flash drive, illuminating LED lights, an 802.11g network card and lithium polymer batteries to power the Goggles. Under the LIIVe program a number of vision based navigation experiments were performed for both cooperative and non-cooperative target inspection.

VERTIGO Goggles: In 2010, the MIT/SSL and Aurora Flight Sciences began the DARPA sponsored VERTIGO (Visual Estimation and Relative Tracking for Inspection of Generic Objects) program. This program was to refine and launch the Goggles developed under the LIIVe program as well as perform additional research on inspection of unknown, non-cooperative targets that are possibly moving and tumbling. The Goggles received a number of minor tweaks and upgrades. The final ISS-flight version of the Goggles are shown attached to a SPHERES satellite at the MIT/SSL (Figure 15).


Figure 15: The VERTIGO Goggles attached to a SPHERES satellite (image credit: MIT)

The processor was upgraded to a Via 1.2 GHz Via Nano, the network card was upgraded to 802.11n, the battery was changed to a unit that was already onboard the ISS, and the optics were upgraded to a larger aperture lens that was in a synchronized stereo configuration. An additional flash drive was added to create a total of 128 GB of storage space. The mechanical design was refined to meet the requirements of operations inside the ISS.

The schematics for the Goggles electronics system and the overall integrated layout is shown in Figures 16 to 18. The average power consumption of the Goggles is approximately 24 W, but can vary between 14 and 30 W depending on the system load.



Figure 16: Cutaway diagram of the integrated VERTIGO Goggles (image credit: MIT)

One of the main design features of the Goggles is future upgradeability. The design incorporates two methods for upgrading future systems. The first is a detachable optics mount . The optics mount contains the CMOS camera sensors, lenses, illuminating LEDs and additional circuitry. The interface between the Goggles avionics stack and the optics mount is an electro-mechanical connection. The mechanical connection consists of four captive thumbscrews which can be removed to detach the optics mount. The electrical connection provides 12 V power, USB, ethernet and RS232 data to interface with the SPHERES and Goggles. The optics mount could be replaced by another piece of hardware that has different sensors or other capabilities. Example upgrades could include cameras in a different configuration or different model, or could even contain a different sensor system entirely (i.e. a LIDAR system). The second method for upgrading the Goggles is via the 802.11n connection. Off-board processing systems could be added that process the images that are captured by the Goggles and streamed over the wireless network.


Figure 17: Front view of the VERTIGO Goggles (image credit: MIT)


Figure 18: Electronics system diagram of VERTIGO Goggles (image credit: MIT)

VERTIGO program status: SPHERES-VERTIGO was launched to the ISS on a Soyuz spacecraft from the Baikonur Cosmodrome, Kazakhstan on October 23, 2012.



SPHERES mission status:

• March 11, 2014: In a breakthrough that will help make it possible for astronauts and robots to work together in deep space, researchers at the Lockheed Martin ATC (Advanced Technology Center) in Palo Alto, CA, working with NASA astronauts aboard the International Space Station, have demonstrated coordinated control of robots in space by astronauts in space and operators on the ground. The breakthrough is the first-ever demonstration of such collaborative teleoperations. The maneuvers create new opportunities to extend the reach of human and robotic missions in Earth orbit and beyond. 31)

Astronaut Karen Nyberg and ATC engineer Humberto Ormeno used an ATC-developed, 3D user interface to command NASA’s SPHERES robots on the space station. Inside the space station, the robots were commanded in “follow-the-leader” exercises and simulated approach-and-docking maneuvers, like those required for in-space assembly of large space structures and asteroid exploration. There is also flexibility within the system, meaning automated control of one or more robots can be combined with manual control of another.

Remote commanding of robots in space, or teleoperation, poses several unique challenges. Commands and telemetry can take one to three seconds to travel between space and the ground via satellite relays, forcing remote operators to predict the effects of their actions using old data. Delicate components designed for weightlessness can be damaged by accidental collisions or even exhaust gases produced by other satellites, so safe maneuvering is essential. The work on the space station is demonstrating how to deal with the time delays associated with signal transfer from the ground.


Figure 19: This formation flight image of SPHERES was taken aboard the ISS during Expedition 16 in the U.S. Destiny laboratory module (image credit: NASA)

• Feb. 25, 2014: The SPHERES satellites have been flying aboard the International Space Station since 2003. Powered by AA batteries, the satellites act as free-flying platforms that can accommodate various mounting features and mechanisms in order to test and examine the physical or mechanical properties of materials in microgravity. 32)

- The DoD “SPHERES-Rings” investigation is the first demonstration of electromagnetic formation flight in microgravity, as well as of wireless power transfer in space. The study installs highly advanced rings to existing SPHERES. The crew places the rings around an individual satellite, consisting of resonant coils, coil housing with fans, batteries and support structure hardware. The Rings project demonstrates the use of electromagnetic coils to maneuver individual SPHERES with respect to one another. The current running through the ring of coils controls the satellites, so that two ring-outfitted SPHERES are able to attract, repel, and rotate.

- Using electrically generated forces and torques is preferable to using fuel, since electricity can be generated by solar panels, but once fuel is expended, the mission is generally over. The research goals for SPHERES-Rings include enhanced attitude control performance between separate satellites and the possibility of more efficient power transfer at a distance. Adding an efficient way to transfer power between SPHERES may alleviate the need for alternate power sources. The wireless power transfer experiment establishes the hardware necessary for potential future powering of space and urban robotics and enhanced communications systems in space, on land, or underwater.


Figure 20: Astronaut Koichi Wakata conducts a session with a pair of SPHERES aboard the ISS (image credit: NASA)

• Feb./March 2013: Inside the JEM/Kibo Laboratory, NASA astronaut Thomas Marshburn worked for the first time with the bowling-ball-sized free-flying satellites SPHERES-VERTIGO which were ground commanded. 33) 34) 35)

- The SPHERES-VERTIGO investigation uses the SPHERES platform on ISS and is designed to demonstrate stereo visual inspection in order to assess close proximity inspection and navigation, including dead reckoning navigation and fiducial-assisted (i.e., navigational tracking marker assisted) navigation and inspection.

- The SPHERES-VERTIGO investigation software incorporates computer vision based navigation and mapping algorithms capable of building a three-dimensional map of another object and performing relative navigation solely by reference to this three-dimensional model.

- In order to test these algorithms, hardware upgrades to the SPHERES facility satellites includes cameras, an upgraded processor, a high-speed communications system and additional batteries.


Figure 21: NASA astronaut Thomas Marshburn conducts a session of the ongoing SPHERES-VERTIGO investigation (image credit: NASA)

• In early 2012, the SPHERES satellites are operational (i.e., they are being used for tests) on ISS (Ref. 40). - So far, MIT has held 32 test sessions onboard the ISS covering research topics such as rendezvous and docking, formation flight, decentralized control, satellite reconfiguration, inertial navigation and other research areas. Additionally, the SPHERES satellites have been used for national and international STEM programming competitions where middle and high school students have programmed the SPHERES satellites that are on-orbit.

• The third annual Zero-Robotics SPHERES Challenge for high school students was conducted at MIT on January 23, 2012. High school student teams from the USA and Europe competed in this event. NASA sponsored the Zero Robotics SPHERES Challenge in partnership with the DARPA (Defense Advanced Research Projects Agency) and MIT. The competition aligns with the agency’s goal of encouraging students to study and pursue careers in STEM (Science, Technology, Engineering and Mathematics). 36) 37) 38) 39)

The objective for this year's challenge: students were given a “mission” to program robots to look for, mine (extracting minerals) and return alternative energy from fictitious asteroids in deep space. They were given coordinates for virtual asteroids located within the ISS and then had to develop computer codes to make a robot perform using various strategies, each of which earned a certain number of points. The free-floating satellites (2 SPHERES) could collect tools if needed and start mining on one of two virtual asteroids.

For the past few months, student teams had been testing their codes in computer simulations, maneuvering virtual robots and competing against other teams in online games. The finalists — 38 teams with the best simulation scores — assembled at MIT on January 23, 2012 for a chance to watch their codes play out in real robots on the ISS. Prior to the competition, NASA had uploaded the software developed by the finalist student teams onto SPHERES in the ISS.

Once NASA successfully connected the MIT auditorium with the ISS, a large screen at the front of the hall projected a live view from inside the station. Astronaut Don Pettit, onboard the ISS, responded, “We hear you loud and clear, MIT.” - Don Pettit and André Kuipers had set up the individual matches in Japan’s Kibo laboratory on the Space Station and enjoyed the spectacle. They presided over the event and gathered data from the student-controlled SPHERES flight programs after each phase of the competition.

Despite a few glitches in the video feed, most teams were able to watch their algorithms in action. During each match, both a red and a blue SPHERE began their missions simultaneously, slowly circling each other and moving about the module according to their preprogrammed trajectories.

The teams “Alliance Rocket“ from the United States and virtual participants “Alliance CyberAvo” from Europe were named the winners in the third annual Zero Robotics SPHERES Challenge.

A total of 38 teams participated in the SPHERES event. Both winning groups consisted of three teams:

- The teams that made up “Alliance Rocket” were Team Rocket, River Hill High School, Clarksville, Maryland; Defending Champions, Storming Robots, Branchburg, New Jersey; and SPHEREZ of Influence, Rockledge High School/Brevard County, Florida.

- “Alliance CyberAvo” consisted of CyberAvo, I.T.I.S. Amedeo Avogrado, Turin, Italy; Ultima, Kaethe Kollwitz Oberschule, Berlin, Germany; and Lazy, Heinrich Hertz Gymnasium, Berlin, Germany.


Figure 22: Astronauts Don Pettit (left) and André Kuipers (right) watch as two SPHERES robots perform their operations as part of the SPHERES Zero-Robotics Challenge (image credit: ESA, NASA, MIT)

• In November 2011, the SPHERES satellites were upgraded with “off-the-shelf” smartphones by using an “expansion port” the MIT team designed into each satellite. Since the SPHERES were originally designed for a different purpose, they needed some upgrades to become remotely operated robots. By connecting a smartphone, the project can immediately make SPHERES more intelligent. With the smartphone, the SPHERES will have a built-in camera to take pictures and video, sensors to help conduct inspections, a powerful computing unit to make calculations, and a Wi-Fi (Wireless Fidelity) connection that the project will use to transfer data in real-time to the space station and mission control. - n order to make the smartphones safer to use onboard the station, the cellular communications chips were removed, and the lithium-ion battery was replaced with AA alkaline batteries.

Until recently, the SPHERES tests used pre-programmed algorithms to perform specific functions. The space station is just the first step to using remotely controlled robots to support human exploration.

By testing the SPHERES satellites, NASA can demonstrate how the smart SPHERES can operate as remotely operated assistants for astronauts in space. NASA plans additional tests in which the compact assistants will perform interior station surveys and inspections, along with capturing images and video using the smartphone camera. Additional goals for the mission include the simulation of free-flight excursions, and possibly other, more challenging tasks. 40)

• SPHERES has operated aboard the ISS since May 2006. The long-duration program continues to provide valuable information for scientists at the MIT Space Systems Laboratory and an array of guest scientists from other institutions. The major milestones of 2006 were achieved in the advancement and demonstration of docking algorithms.

• Throughout 2007 and 2008 the research SPHERES expanded to include substantial research in formation flight algorithms (Table 4). 41) 42)

TS (Test Session)


Science configuration/goal


March 24, 2007

2-Sat Lost-in-Space, 3-Sat Formation Flight


April 27, 2007

3-Sat Formation Flight


December 12, 2007

2-Sat Formation Initialization & Scatter


January 27, 2008

2-Sat Formation Initialization & Scatter


August 30, 2008

2-Sat Spiral Formations


September 27, 2008

3-Sat Collision Avoidance


Oct/Nov. 2008

3-Sat Simulated comm & thruster failures, 2-Sat Spiral Formations

Table 4: Overview of SPHERES Test Sessions (TS) on ISS with formation flight research objectives

Three-satellite formation flight experiments began in TS7 with basic circular formations. The research then grew into two main areas: control of rotating formations and algorithms to provide autonomy for distributed satellite systems. An extensive set of algorithms was developed based on the need for satellite formations to reconfigure in response to operational goals and the status of individual satellites.

The SPHERES developments include tasks on four main areas:

• Imaging maneuvers: creation of circles and spirals to simulate the motions of potential separated spacecraft radar/telescopes.

• Formation acquisition: algorithms to initialize a formation from random initial conditions, including “Lost-in-space” algorithms, optimally joining an existing formation, and random selection of a formation leader.

• Formation maintenance: geometry reconfiguration, low-level collision avoidance, use of different sensor information, and changing between relative and absolute frames of reference.

• Fault detection and recovery: reconfiguration after a (simulated) satellite failure (sensors, actuators, and/or communications), scattering of operational satellites to avoid a failed satellite.

The 2007 and 2008 SPHERES formation fight tests concentrated on imaging maneuvers and autonomy algorithms. The imaging maneuvers used a wide range of controllers: PID (Proportional Integral Derivative), LQR (linear Quadratic Regulator), and cyclic pursuit. The use of basic PID controllers in circles was sufficient. But LQR controllers did not provide acceptable performance in spirals, exposing the need to use more complex controllers as the dynamics of spirals did not prove to be a simple extension of circular motion. The use of the decentralized controller resulted in the best performance to follow a spiral path (Ref. 41).

The autonomy algorithms covered a wide range of possible actions which must be taken by a distributed satellite system. Formation initialization from random deployment conditions tests allowed the team to identify multiple potential problems which would cause an algorithm to fail; these issues are sometimes directly related to the algorithm (e.g. potentially having no formation “leader”) and also from other parts of the satellite (e.g. loosing communications).

The lessons learned from the development of scatter maneuver algorithms include the somewhat obvious need to fully identify your surroundings, but also the importance of a scatter maneuver to dynamically determine the scatter direction. All satellites should move in opposite directions from each other, rather than move to a pre-determined “safe” location.

The collision avoidance tests demonstrated the ability to use a low-overhead process to enable this autonomous behavior on spacecraft systems. The tests have provided initial data to fully understand the empirical relationship between operational noise (i.e., deviations from an ideal path) and the “safety” box around a physical system.

The SPHERES team proposed two different methods for a formation flight system to recover from potential failures of one of the satellites. For communications failure, where the failed satellite is expected to be able to stop its motion, the suggested recovery is to change the plane of the formation. For thruster failures, the team suggests that a scatter maneuver is necessary to safeguard the operational satellites. The thruster failure simulation test demonstrated the validity of the scatter maneuver for this type of failure.

• SPHERES’s Test Session 12 was performed on August 30, 2008, onboard the International Space Station by the NASA Astronaut Greg Chamitoff. This Test Session included the Continuous Spiral Maneuver Tests. The visual inspection of the real video provided by NASA on the same day of the test session, proved the correct behavior of the trajectory planning algorithm and the implementability of these kind of coordinated trajectories in space.


Figure 23: Astronaut Gregory Chamitoff, an MIT alumnus, is attending a SPHERES formation flight test (image credit: MIT)

1) S.-J Chung, D. Adams, A. Saenz-Otero, E. Kong; D. W. Miller, D. Leisawitz, E. Lorenzini, S. Sell, “SPHERES Tethered Formation Flight Testbed: Advancements in Enabling NASA's SPECS Mission,” Proceedings of SPIE Astronomical Telescopes and Instrumentation Symposium, Orlando, FLA, May 2006, SPIE paper 6268-11, `Advances in Stellar Interferometry,' URL:

2) A. Saenz-Otero, D. Miller, “The SPHERES ISS Laboratory for Rendezvous and Formation Flight,” 5th International ESA Conference on Guidance Navigation and Control Systems, Frascati, Italy, Oct. 22-25, 2002, SP-516

3) D. W. Miller, E. M. C. Kong, A. Saenz-Otero, “Overview of the SPHERES Rendezvous and Docking Laboratory on the International Space Station,” Proceedings of the 26th AAS Conference on Guidance and Control, Breckenridge, CO, Feb. 5-9, 2003, Vol. 113, Advances in the Astronautical Sciences, Edited by I. J. Gravseth and R. D. Culp, AAS-03-013, pp. 155-169

4) S.-J. Chung, E. M. Kong, D. W. Miller, “Dynamics and Control of Tethered Formation Flight Spacecraft Using the SPHERES Testbed,” Proceedings of the AIAA Guidance, Navigation, and Control Conference and Exhibit, San Francisco, CA, USA, Aug. 15-18, 2005, AIAA 2005-6089, URL:


6) A. Saenz-Otero, D. W. Miller, “Using ISS to develop telescope technology,” URL:

7) D. Miller, D. Newman, J. de Luis, “Synchronized Position, Hold, Engage, and Reorient Experimental Satellites (SPHERES), Test Equipment Data Package,” March 23, 2000

8) A. Saenz-Otero, D. Miller, “SPHERES: a platform for formation-flight research,” Proceedings of the SPIE, Vol. 5899, pp. 230-240 (2005), ``UV/Optical/IR Space Telescopes: Innovative Technologies and Concepts II,' San Diego, CA, August 2005, URL:

9) J. Enright, M. Hilstad, A. Saenz-Otero, D. Miller, “The SPHERES Guest Scientist Program: Collaborative Science on the ISS,” Proceedings of 2004 IEEE Aerospace Conference, Big Sky, MT, March 6-13, 2004

10) S. W. Sell, S. E. Chen, “SPHERES: Design of a Formation Flying Testbed for ISS,” Proceedings of IAF, 34th COSPAR Scientific Assembly, The Second World Space Congress, Oct, 10-19, 2002, Houston, TX, USA

11) A. Chen, A. Saenz-Otero, M. Hilstad, D. Miller, “Development of Formation Flight and Docking Algorithms Using the SPHERES Testbed”, 15th Annual AIAA/USU Conference on Small Satellites, Utah State University, Logan, UT, August 13-26, 2001, SSC01-VIIIa

12) D. Miller, A. Saenz-Otero, J. Wertz, A. Chen, G. Berkowski, C. Brodel, S. Carlson, D. Carpenter, S. Chen, S. Cheng, D. Feller, S. Jackson, B. Pitts, F. Perez, J. Szuminski, S. Sell, “SPHERES: A Testbed For Long Duration Satellite Formation Flying In Micro-Gravity Conditions,” Proceedings of the AAS/AIAA Space Flight Mechanics Meeting,, Clearwater, FL, USA, Jan. 23-26, 2000, AAS 00-110, URL:


14) D. Berkovitz, E. Kong, D. Miller, “System Identification of the SPHERES Autonomous Rendezvous and Docking Testbed,” Space 2003, 23 - 25 September 2003, Long Beach, CA, USA, AIAA 2003-6385

15) R. Lim, D. Miller, “Staged Attitude-Metrology Pointing Control and Parametric Integrated Modeling for Space-based Optical Systems,” Thesis at MIT, May 2006, URL:

16) E. M. Kong, A. Saenz-Otero, S. Nolet, D. S. Berkovitz, D. W. Miller, S. W. Sell, “SPHERES as a Formation Flight Algorithm Development and Validation Testbed: Current Progress and Beyond,” URL:

17) Amer Fejzic, Simon Nolet, Louis Breger, Jonathon P. How, David W. Miller, “Results of SPHERES Microgravity Autonomous Docking Experiments in the Presence of Anomalies,” Proceedings of the 59th IAC (International Astronautical Congress), Glasgow, Scotland, UK, Sept. 29 to Oct. 3, 2008, IAC-08.C1.5.1

18) Simon Nolet, Alvar Saenz-Otero†, David W. Miller, Amer Fjezic, “SPHERES Operations Aboard the ISS: Maturation of GN&C Algorithms in Microgravity,” Proceedings of the 30th Annual AAS Guidance and Control Conference, Breckenridge, CO, USA, Feb. 3-7, 2007, AAS 07-042



21) J. Enright, M. Hilstad, A. Saenz-Otero, D. Miller, “The SPHERES Guest Scientist Program: Collaborative Science on the ISS,” IEEE Aerospace Conference 2004, Big Sky, Montana, March 6-13, 2004, Paper No 1296

22) A. Saenz-Otero, D. W. Miller, “Initial SPHERES Operations Aboard the International Space Station,” Proceedings of the 6th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 23 - 26, 2007

23) M. O. Hilstad, J. P. Enright, A. G. Richards, “The SPHERES Guest Scientist Program,” MIT documentation, Oct. 29, 2003, URL:

24) D. P. Scharf, F. Y. Hadaegh, S. R. Ploen. “A Survey of Spacecraft Formation Flying Guidance and Control. Part I: Guidance,” Proceedings of the American Control Conference, Vol. 2, pp. 1733-1739, June 4-6, 2003, Denver, CO, USA

25) G. S. Aoude, J. P. How, D. W. Miller, “Reconfiguration Maneuver Experiments Using the SPHERES Testbed Onboard the ISS,” Proceedings of the 3rd International Symposium on Formation Flying, Missions and Technology, ESA/ESTEC, Noordwijk, The Netherlands, April 23-25, 2008

26) Alvar Saenz-Otero, Jacob Katz, Swati Mohan, David W Miller, Gregory E Chamitoff, “ZERO-Robotics: A Student Competition aboard the International Space Station,” Proceedings of the 2010 IEEE Aerospace Conference, Big Sky, MT, USA, March 6-13, 2010

27) Brent E. Tweddle, Elias Müggler, Alvar Saenz-Otero, David W. Miller, “The SPHERES VERTIGO Goggles:Vision based mapping and localization onboard the International Space Station,” Proceedings of i-SAIRAS (International Symposium on Artificial Intelligence, Robotics and Automation in Space), Turin, Italy, Sept. 4-6, 2012, URL:

28) Brent E. Tweddle, “SPHERES VERTIGO Program: Vision Based Navigation Research onboard the International Space Station,” IEEE IRCA (International Conference on Robotics and Automation), Shanghai, China, May 9-13, 2011, URL:

29) Alvar Saenz-Otero, “SPHERES - Maturation of Autonomous Rendezvous & Docking Algorithms with SPHERES aboard the ISS,” IEEE ICRA 2012, Satellite Servicing Workshop, St. Paul, MN, USA, May 14-18, 2012, URL:

30) Jennifer Chu, “Research update: SPHERES to get powerful magnets and goggles,” MIT News Office, Aug. 02, 2012, URL:

31) “Lockheed Martin Researchers Achieve Breakthrough in Robotics for Space Exploration,” Lockheed Martin, March 11, 2014, URL:

32) “NASA SPHERES Run Circles Around Ordinary Satellites,” NASA Tech Briefs, Feb. 25, 2014, URL:

33) “Lead Increment Scientist's Highlights for the Week of Feb. 25, 2013,” NASA, March 8, 2013, URL:

34) “Synchronized Position, Hold, Engage, Reorient, Experimental Satellites - VERTIGO (SPHERES-VERTIGO),” NASA, Feb. 25, 2013, URL:

35) Dehann Fourie, “VERTIGO - Vision based Navigation and Mapping of an object,” MIT, March 14, 2013, URL:

36) Ann Marie Trotta,“Zero Robotics Challenge Winners Decided in High-Tech Competition,” NASA, Jan. 24, 2012, URL:

37) Jennifer Chu, “Robots go head to head, 250 miles above Earth,” <mit News Office, January 25, 2012, URL:

38) “Robot competition in zero-gravity,” ESA, Jan. 25, 2012, URL:

39) Sreeja Nag, Ira Heffan, Alvar Saenz-Otero, Mike Lydon, “SPHERES Zero Robotics Software Development: Lessons on Crowdsourcing and Collaborative Competition,” Proceedings of the 2012 IEEE Aerospace Conference, Big Sky, Montana, USA, March 3-10, 2012

40) Ray Sanders, “NASA Channels “The Force” With Smart SPHERES,” Universe Today, Jan. 5., 2012, URL:

41) Alvar Saenz-Otero, Jacob Katz, David W. Miller, “SPHERES Demonstrations of Satellite Formations aboard the ISS,” Proceedings of the 32nd AAS Guidance and Control Conference, Breckenridge, CO, USA, Jan. 31.- Feb. 4, 2009, AAS 09-011

42) M. Diiaz-Aguilo, C. Mandy, A. Saenz-Otero, D. Miller, “Optimal Interferometric Maneuvers for Distributed Telescopes,” Proceedings of the 60th IAC (International Astronautical Congress), Daejeon, Korea, Oct. 12-16, 2009, IAC-09.A3.4.7

The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.