Debris May Be Issue as Fuel-depleted GOCE Moves Toward Early November Re-entry

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PARIS — Europe’s GOCE gravity measurement satellite ran out of fuel Oct. 21 and will be pulled into the atmosphere in about two weeks, from where it will be tracked by ground radars to monitor any pieces that might survive and hit Earth.

The 20-nation European Space Agency (ESA) said its Darmstadt, Germany-based Space Debris Office, and radars from other national members of the Inter-Agency Space Debris Coordination Committee, will be trained on GOCE to pinpoint its descent and, if needed, warn shipping lanes or affected populations.

GOCE, or the Gravity Field and Steady-State Ocean Circulation Explorer, weighed 1,052 kilograms at launch including some 41 kilograms of xenon fuel used for its ion-electric propulsion system.

The satellite, with a striking, arrowhead-shaped design and winglets, measures 5 meters long with a 1.1-square-meter cross section. ESA said the chances of some pieces of the satellite surviving atmospheric re-entry are high.

But with about two weeks to go before re-entry, ESA said, it is too soon to estimate where the re-entry might occur on GOCE’s orbit. As is the case with any object on an uncontrolled re-entry, the chance of GOCE pieces landing on water are about the same 70 percent as the percent of Earth’s landmass covered by water.

ESA teams will continue to operate GOCE and collect data from it until its on-board systems cease functioning, at which point GOCE will be switched off.

The mission, launched in March 2009, was scheduled to last just two years, but an unusually long period of mild solar activity enabled GOCE managers to conserve fuel that otherwise would have been spent to maintain GOCE in orbit despite the pull of the upper atmosphere.

GOCE’s operating orbit was 255 kilometers. Once its nominal mission was completed in mid-2012, GOCE’s orbit was further lowered, to 224 kilometers, to capture more-detailed measurements.

At an orbit this low — one GOCE manager said the mission was less remote sensing than “in-situ sensing” — program managers knew GOCE’s fuel supply would drain more quickly.

Notwithstanding that GOCE ground teams’ work has flipped from gravity measurements to debris monitoring, the satellite’s mission was judged to be a clear success.

“The results are fantastic,” ESA Earth Observation Director Volker Liebig said in an Oct. 21 statement. “We have obtained the most accurate gravity data ever available to scientists. … New results are emerging constantly.”

 

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