European Gravity Probe Returned to Normal Orbit

Europe?s gravity-measuring GOCE satellite has returned to its exceptionally low operating orbit after a series of maneuvers that successfully compensated for a July anomaly that had shut down the satellite?s ability to transmit science data, the European Space Agency (ESA) announced Sept. 29.

A pair of apparently unrelated malfunctions in and around the computer system of the Gravity Field and Steady-State Ocean Circulation Explorer had stopped data telemetry and forced ESA managers to raise GOCE?s orbit to 263 kilometers, some 7 kilometers above its optimal operating altitude, while they worked to correct the problem.

The higher orbit was needed so that GOCE?s flight path could be maintained more easily even if its xenon-ion electric propulsion system was switched off for brief periods during the corrective maneuvers. During normal GOCE operations, these engines provide thrust to counter drag on the satellite?s orbital motion caused by residual atmosphere. With telemetry now restored, the satellite has been returned to its normal orbit and is providing its full complement of data.

GOCE was launched in March 2009 on a two-year mission. It had already compiled two-thirds of its planned data harvest by the time its computer problems occurred. Because of the unusually low solar activity in 2010, GOCE used less drag-compensating fuel than forecast. Its managers said they are likely to propose a mission extension beyond 2011.

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