European satellite GOCE Will Have an Uncontrolled Reentry

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European Space Agency (ESA) has confirmed that the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite is preparing to reenter to Earth between the end of this month and the start of November.

“Some satellites take decades to come back after finishing operations; we will reenter in no more than three weeks,” ESA mission manager Dr Rune Floberghagen told BBC.

This will be the first uncontrolled reentry of an ESA satellite since Isee-2, in 1987. Unfortunately, it will not be the last, considering that the bus-size Envisat’s altitude is gradually decaying in Low-Earth Orbit without control.  According to ESA, up to 25% of GOCE’s mass will survive the extreme reentry conditions to fall to the ground. However, the risk for populated areas is very small since the majority of the Earth is covered by oceans.

The fragments that survive will hit the ground in a 900 km long footprint. The reentry will be a good test for debris monitoring systems and fragmentation models.

In 2011 and 2012, the reentries of NASA’s UARS spacecraft and failed Russian probe Phobos-Grunt raised many  concerns about safety for people on the ground, not only for the chance of being hit by fragments, but also for pollution from hydrazine propellants used in the spacecraft.

Before reentry, ESA engineers will fully passivate GOCE, depleting its xenon fuel tank and switching off its transmitter so as not to interfere with other satellites.

Image Caption: Artist’s conception of GOCE orbiting Earth (Credits: ESA).