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ESA overcomes glitch on gravity-mapping satellite

The European Space Agency’s GOCE satellite is again collecting data on Earth’s gravitational field after a computer glitch disrupted the flow of scientific communications to the ground.

GOCE has been out of commission since July, when the arrow-shaped satellite suffered a computer malfunction that engineers later traced to a communications link between processor and telemetry modules in a backup unit.

Ground controllers at the European Space Operations Center in Germany switched GOCE to a redundant B-side computer in February after an unexplained chip failure crippled the primary unit. ESA says the problems are apparently not related.

The July anomaly prevented GOCE science data from reaching the ground, and engineers were devising software patches to connect working functions of the two computers to restore full capacity.

But the recovery came sooner than expected as ESA commanded a rise in temperature inside the satellite’s computer compartment.

“We are very glad that one of the most innovative missions of ESA is back on track,” said Volker Liebig, director of the agency’s Earth observation programs. “I would like to congratulate and thank the teams from ESA and especially industry.”

GOCE resumed normal communications after the temperature increased by about 7 degrees Celsius, according to ESA.

Engineers are still developing software patches to link the two computers should the communications system suffer the same problem again, an ESA statement said.

The $444 million Gravity field and steady-state Ocean Circulation Explorer, or GOCE, mission is creating an exceptionally accurate map of the planet’s geoid, a global model illustrating subtle variations in the gravity fields, assuming oceans were motionless.

Scientists use the geoid’s reference surface to compare against measurements of ocean activity, allowing oceanographers to more accurately study ocean circulation and sea level changes.

GOCE’s gradiometer, the mission’s scientific instrument, was turned back on Monday and is working well, said Rune Floberghagen, the satellite’s mission manager.

“With everything back in proper working order, the satellite is now being gently brought back down to its operational status and altitude,” Floberghagen said. “This should be achieved before the end of September.”

Officials raised GOCE’s unusually low orbit by about 10 kilometers, or 6 miles, to buy more time during the recovery effort.

GOCE is circling nearly 165 miles above Earth, an altitude that is prone to fluctuations in atmospheric drag caused by increased solar activity. Controllers boosted the satellite to ensure it would not be dragged back into the atmosphere in case the computer glitch spread to GOCE’s ion thruster or navigation systems.

GOCE’s ion thruster produces a steady stream of thrust to keep the satellite at a stable altitude.

In an Aug. 27 interview, ESA’s chief of Earth observation mission science said the spacecraft is working well besides the unlucky computer mishaps.

Mark Drinkwater, also a former GOCE scientist, said the satellite has enough xenon gas for its ion engine to continue operating through the end of 2012, well beyond the anticipated end of the mission in April 2011.

GOCE has already delivered two-thirds of the gravity data expected from the mission, according to an ESA press release. The mission is designed to produce measurements 100 times better than its predecessors.

“We have a significant degree of data in the back from the nominal mission,” Drinkwater told Spaceflight Now. “We’re making huge scientific progress with the data we’ve already got.”

Source ESA