GOCE is out of fuel

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The European Space Agency has announced the end of the GOCE mission. In two or three weeks the satellite will reenter into the Earth’s atmosphere.

The Gravity Ocean Circulation Explorer (GOCE) mission began on the 17th of March 2009. The satellite was inserted into a very low Earth orbit with the initial altitude of 280 km. In order to withstand a measurable atmospheric friction at such orbit, GOCE was equipped with an ion engine and a slender body. In order to improve control, two small stabilizers were also added to satellite. The European Space Agency (ESA) has maintained the GOCE mission.

Such a low orbit was selected for scientific reasons. The GOCE mission performed very precise measurements of Earth’s gravitational field and water circulation in the oceans. For over 4 years GOCE acquired precise data, including the effects created by the strong earthquake in Japan in March 2011.

During the mission, the orbit of GOCE was gradually lowered. Initially, the satellite was placed into a 280 km orbit, which was later lowered to 270 and then to 255 km. In November 2012 the satellite was lowered to 235 km and in May 2013 to a mere 229 km. After launch GOCE’s fuel tank was filled with 41 kg of xenon fuel for the ion engine. In September, the remaining fuel was just 2 kg.

Some analyses from the beginning of September suggested that GOCE would run out of fuel most likely on the 16th or 17th of October. This has not happened then – on 18th of October GOCE still had 350 grams of xenon fuel. However on that day the feed line pressure to the ion engine dropped below 2,5 bars, which was a nominal value during the mission. At that time ESA calculated that GOCE will run out of fuel before the 26th of October. Finally, the fuel tank was emptied on the 21st of October.

In about two to three weeks from now, GOCE will be destroyed once it enters the denser parts of the atmosphere. At the altitude of around 80 km the satellite will break into dozens of fragments. It is estimated that about 250 kg of GOCE’s debris split into in 40-50 pieces will reach the surface of our planet. The zone, where GOCE’s fragments will fall, is 900 km long. Right now it is not possible to predict, where GOCE will reentry, but since it is on a polar orbit, debris might hit practically every point on Earth.

Apart from its ion engine, the satellite is still functional and over the next two weeks the data from its instruments will be acquired.

The mission was designed to last for 20 months. But due to very low solar activity in this cycle and thus a lower density of the Earth’s atmosphere, GOCE is already over four and half years on orbit.

For the next few weeks Kosmonauta.net will aggregate and publish information about GOCE’s fiery descent from orbit.

(ESA, PFA)

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