Engineers rescue aging satellites, saving millions

A new technique to save aging satellites promises to save millions of dollars by extending the life of communications spacecraft. A process developed by researchers from Purdue University and Lockheed Martin has already saved $60 million for unnamed broadcasters by extending the service life of two communications satellites.

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

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, researchers said in a paper published in the most recent Journal of Spacecraft and Rockets. Enough fuel must remain to get the satellites out of orbit to make room for their replacements.

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 said Steven Collicott a Purdue professor of aeronautics and astronautics in a statement.

Adjusting the levels of fuel in an orbiting satlite is no simple task. The problem's complexity is illustrated by the level of skills needed, said Collicott, adding that most researchers involved in such work have doctoral degrees in aerospace engineering.

The research paper details two portions of the work needed to accomplish the fuel equalization: how to perform the "thermal gauging" that determines how much propellant is contained in the tanks, and then how to accomplish the rebalancing.

"It took a year and a half of thermal pumping, carried out at different times, to accomplish the rebalancing," Yendler said. "We were really excited to see that we could take our new propellant-gauging method to provide this lifetime maximization in satellites that were never designed to have anything like this done to them."Communications satellites cost about $100 million and sometimes as much money to launch them into a geosynchronous orbit. They generally have a 15-year lifetime, bringing in $5 million to $10 million a month in revenue.

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