Engineers Rescue Aging Satellites, Saving Millions

Researchers have used a new technique to save $60 million for broadcasters by extending the service life of two communications satellites.

The technique works by applying an advanced simulation and a method that equalizes the amount of propellant in a series of fuel tanks so that the satellite consumes all of the fuel before being retired from service.

The two satellites would have been shut down prematurely and wasted remaining fuel if not for the new technique developed by researchers from Purdue University and Lockheed Martin Corp., says Steven Collicott, a Purdue professor of aeronautics and astronautics.

Communications satellites, which are maintained in proper orbit about 22,500 miles above Earth by firing small rocket thrusters, must be replaced shortly before they run out of fuel. Enough fuel must remain to get the satellites out of orbit to make room for their replacements.
Some aging communications satellites are each equipped with four fuel tanks. If one of the tanks empties before the others, the satellite loses control and should be decommissioned, wasting the remaining fuel in the other tanks, says Boris Yendler, senior thermal system analyst at Lockheed Martin Mission Services in Sunnyvale, Calif.

The Purdue and Lockheed Martin engineers not only determined precisely how much fuel remained in each tank, but they also used a technique to "rebalance," or equalize, propellant levels in all of the tanks. The engineers kept the twin satellites operating an additional six months, which translates into about $60 million in revenue for the broadcast companies that owned the satellites, Collicott said.

This work, led by Yendler, represents the first time such a fuel gauging and rebalancing has been carried out in commercial communications satellites," Collicott says.

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