Satellites that fly in formation

Just as we have progressed from giant mainframe computers to small networked PCs, so researchers at the Massachusetts Institute of Technology believe that teams of synchronised nanosatellites will replace the bulkier machines currently orbiting our planet.

MIT’s SPHERES (Synchronised Position Hold Engage Re-orient Experimental Satellites) experiment is just one of a number of projects aimed at designing satellites that will fly in perfect formation.

The project, headed up by Professors David Miller and Dava Newman of the Department of Aeronautics and Astronautics, has so far led to the development of three football-sized satellites. Two of these devices, which communicate with each other and a computer, were recently tested aboard NASA’s KC-135 airplane, affectionately known as the `vomit comet’, which allows satellites (and researchers) to become weightless for short periods of time. The team successfully operated two SPHERES at the same time inside the plane, collecting data that helped improve the devices for the next mission.

This is the first time that the Department has offered undergraduates the opportunity to design, implement, and test a product within one course. `It gives them a lifecycle experience in the development of an aerospace product,’ said Professor Miller.

While the ultimate goal would be to have teams of satellites flying around in space, the current SPHERES are intended for use only on board the space shuttle or inside the International Space Station, where astronauts will use them to test different parameters related to formation flying. The satellites were created to `research and validate key formation flight technologies,’ commented Miller.

Scientists will, for example, test different control algorithms, as well as metrology (how the system measures things and how it navigates) and autonomy (how each unit can make decisions on its own without human intervention).

On Earth and aboard the KC-135 the SPHERES can manoeuvre in different directions, and identify their positions with respect to each other, but even the most careful ground-based tests are not truly representative of conditions in space, where the SPHERES have many more degrees of freedom.

Looking further into the future, one application for this technology is thought to be in the creation of a telescope with a higher resolution than the Hubble, which would work by stringing several tiny satellites fitted with mirrors across the sky, an exercise which will require very accurate control of the satellites.

In a similar project – a joint effort between the Arizona State University, the university of Colorado, and New Mexico State University scientists claim that teams of satellites will be ideal for observing and predicting earth’s weather patterns.

The objective of the Three Corner Sat project is to use three small satellites to stereo image dynamic scenes in space. By using a formation of satellites, stereo images of small, dynamic objects can be made, and used to calculate range. This, say the researchers, will enable the study of small-scale, short-lived atmospheric events such as cumulus-cloud towers. These formations, which extend from the middle troposphere into the lower stratosphere, are impassable to air traffic due to the highly unstable air, and radar cannot give accurate data as to their altitude. Nanosatellites could, say the team, allow us to make better estimates of cloud heights, and cut down on unnecessary air traffic diversions.

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