A satellite that mapped the Earth’s gravity for four years has been caught by its pull and, with the mission over, started its uncontrollable descent, the ESA’s first re-entry of this kind since 1987.
Now, with the xenon gas expired, scientists at the European Space Agency have literally no way of steering the vessel, so hopes are high everything will go smoothly and no damage will be caused down on Earth..
It was 25 years ago that the ESA last attempted such a free-fall, during the Isee-2 magnetosphere mission.
“Reentry into the atmosphere [is] probably less than two days away,” Christoph Stieger, the European Space Agency’s operations manager for the satellite, said in a status report on the ESA’s website.
The space agency’s one-ton Gravity field and steady-state Ocean Circulation Explorer, or GOCE, was launched from Plesetsk, in northern Russia, in 2009.
Having spent 2 1/2 more years on its mission than originally planned, it was taken to extremely low orbits with the aim of providing gravity data of unparalleled accuracy.
“This innovative mission has been a challenge for the entire team involved: from building the first gradiometer for space to maintaining such a low orbit in constant free-fall, to lowering the orbit even further,” said Volker Liebig, ESA’s director of Earth observation programs. “The outcome is fantastic. We have obtained the most accurate gravity data ever available to scientists. This alone proves that GOCE was worth the effort – and new scientific results are emerging constantly.”
The $466 million satellite’s sleek aerodynamic design led to it being nicknamed the “Ferrari of space.”
In late October, the satellite’s supply of xenon gas ran out; however, for two more weeks the satellite continued its orbit until its engines died and it started the inevitable fall to Earth.
The problem scientists are faced with now is, despite knowing that most of GOCE will burn up in Earth’s atmosphere, around 50 fragments of debris weighing in at about 275 kilograms will slip past it. This means they could end up falling literally anywhere.
The lack of knowledge is caused by constant changes in the Earth’s upper atmosphere, which are influenced by solar activity.
An international campaign involving the Inter-Agency Space Debris Coordination Committee is monitoring the situation continuously, the ESA said, promising to “keep the relevant authorities permanently updated.”
Scientists at NASA estimate that an average of one piece of falling space debris daily survives the Earth’s atmosphere. They are confident that the chances of debris causing serious damage are small, as the record of even property damage has been almost negligible in the last half-century.
That assumption is based on the simple fact that two-thirds of the planet is covered in water, and that most of the Earth’s land masses are quite sparsely populated.
Russian, American and German satellites have fallen in the past, often in circumstances involving the failure of an engine at very low orbits. Though no substantial damage was ever reported, debris as heavy as 160-400 kilograms had previously fallen within hundreds of kilometers of populated areas in the Pacific.
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