The SPHERES Program
History of the Program
SPHERES began in 1999 as a project for a senior capstone course in the department of aerospace engingeering. The course was a three semester class that used the Concieve, Design, Implement, Operate (CDIO) model. Students took the project from the initial idea through the entire design and build process and in the process recieved hands on experience producing an aerospace system. Professor David Miller challenged the students to develop a device similar to the training drone seen in Star Wars, Episode 4. Several prototypes were produced and tested, both on the flat floor and on parabolic flights.
At the conclusion of the CDIO course SPHERES was taken over by the Space Systems Laboratory. The SSL refined the design and produced six flight-ready satellites. Shuttle flights were suspended after the Columbia disaster in 2004, delaying the launch of the flight hardware. The SPHERES finally reached space in 2006.
The first test session ocurred on May 18th, 2006. Over the first few test sessions the SPHERES were configured and tested. A few issues with the graphical user interface and with the device memory were encountered, but all were swiftly resolved. Reaserch with SPHERES has continued ever since.
The SPHERES Satellite
The satellite is roughly spherical and about the size of a bowling ball. The frame is aluminum, and the components are enclosed in a plastic shell. Each satellite has its own color.
The device uses a cold gas propulsion system: jets of pressurized gas released from thruster propel and allow control. There are twelve of these thrusters located in opposing pairs all around the satellite. Together they allow translation in all three dimensions and rotation around all three axis. SPHERES can move in six degrees of freedom.
Navigation is aided by a set of ultrasound beacons around the testing environment. The satellites have infrared transmitters, which allow them to ping the beacons. When pinged the beacons respond with an ultrasound pulse in a predetermined sequence. By measuring what direction the responses come from the satellite determines its location relative to the beacons, and relative to the other SPHERES.
The satellites are controlled by a wireless link to a standard laptop. A small plastic transmitter connects to the laptop and establishes communication with the SPHERES. They can either be flown manually or be programmed to perform manouvers automatically.
Programs for automatic manouvers are written in C, and loaded to the satellites by the wireless communications link. SPHERES has very little processing power, only enough to manage the sensors and thrusters on board. Additional processing power for other applications is provided by the VERTIGO Avionics Stack.
SPHERES was designed to be expandable. A port on one face allows add-ons to the satellite. In the years since the program began additional hardware has been developed, including cameras, an electromagnetic propulsion unit, docking ports and more. More information about aditional hardware is acessible through the projects tab to the left.
Operations on the ISS
The sattelites fly inside the Japanese Experiment Module of the station. For a typical test session, astronauts first set up the five IR beacons and a laptop, and take the SPHERES out of storage and set them up. If additional hardware is needed it's attatched to the SPHERES as well. The program being tested is loaded to the satellite. The program runs; the behavior of the SPHERES is observed and the results are filmed and recorded. Another program is loaded, and several more tests are run. The scientists on the ground use these results to evaluate and improve the algorithim or technology being tested. The whole proccess takes five to six hours, with the SPHERES running for approximately an hour minutes total. Over sixty test sessions have been conducted using the SPHERES system, making SPHERES one of the most prolific experiments on the station. SPHERES is also popular with the astronauts, and many have stated that it is their favorite experiment.
The Future of the Program
In the first years of operation, SPHERES served first and foremost as a controls testbed; a platform to test algorithms and methods for the control of satellites flying in formation. Consequently, its capabilites are limited to the ability to move and rotate in three dimensions. In the coming years, the SSL aims to expand the capabilities of SPHERES drastically. INSPECT and VERTIGO improve the satellite's ability to perceive its environment; UDP and ARM will improve its ability to interact with the environment. With Halo, SPHERES will experiment with reconfigurable structures. SPHERES will investigate proximity operations; operating near another craft while maintaining distance. The suite of new hardware will allow the SPHERES to do more than ever before, opening an exciting new range of uses for the satellites.
The SSL intends to eventually develop a spacecraft capable of operating outside the ISS. NASA has stated a need for free-flying autonomous vehicles, capable of flying outside the space station. In the coming years the SSL will work to develop SPHERES-X, a SPHERES like system capable of operating outside of the International Space Station. SPHERES-X is envisioned as a way to inspect the outside of the ISS, as well as a platform for free floating experiments outside of station.
To develop this system considerable improvments must be made to almost all aspects of SPHERES. It is with this in mind that the SSL is developing the hardware to expand the capabilities of SPHERES.
Autonomus free floating craft have enormous potential, but also considerable risk. Anything moving in the space surrounding the ISS has the potential to damage the station. The exterior of the station is not designed to withstand impacts, so considerable effort must be made to guarantee any vehicle outside the station is absolutely safe.
If those challenges are overcome, though, the rewards would be tremendous. Currently operations on the exterior of the station must be done by an astronaut in a space suit during an Extra Vehicular Activity (EVA). A robotic inspection vehicle would considerably increase the capailities to operate around the station.