Computer Glitch Deemed No Threat to GOCE Mission

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BERGEN, Norway — Europe’s GOCE gravity-measuring satellite, which began operations late last year, has lost the use of one of its two on-board computers in what program managers said is a rare, and still-unexplained, failure of a well-proven computer chip.

They said that given the flight history of the component, they are not overly concerned that the backup system, which uses the same chip, will also fail.

“This is the first time this has happened with this chip so far as we can tell,” said Reiner Rummel, chairman of the Gravity and steady-state Ocean Circulation Explorer (GOCE) satellite’s advisory group. The satellite was launched in March 2009 on a two-year mission.

GOCE managers said the satellite is performing flawlessly otherwise. Given the unusually long calm period in the current solar cycle, GOCE has been able to operate at its extremely low orbit without as much hindrance from solar activity as would have been the case if the sun had been more active, and program managers said it is all but certain to fulfill its mission.

The winged GOCE, shaped like a crude arrowhead, has produced its first global map of the minor differences in gravitational attraction of different parts of the Earth. The map — the first of its kind — was released here June 29 during the Living Planet Symposium organized by the 18-nation European Space Agency (ESA). The data are the result of two months of GOCE measurements starting last November. Rummel said the map will be improved with successive two-month updates. “We are still in the learning phase,” he said.

GOCE’s 255- to 260-kilometer orbit is the lowest operating orbit ever flown by a satellite whose orbital data were published. The low orbit, necessary to permit GOCE’s six accelerometers to measure the differences in the Earth’s gravity pull, puts the satellite in contact with the Earth’s residual atmosphere. To compensate for this drag, the satellite is fitted with small ion thrusters.

GOCE Mission Manager Rune Floberghagen of ESA said an ongoing investigation into the cause of the computer failure has already concluded that the chip is not part of a possibly defective series. “Others that were part of the same lot have flown without problems, and in fact this chip series has flown thousands of orbits,” he said.

Rummel said GOCE mission managers have not abandoned an effort to overcome the chip failure and return the computer to service. But for now, he said, GOCE is working fine and there is no sense of urgency about the mission’s duration.