The final launch simulation for the European Space Agency’s comet-chasing Rosetta mission was completed on Wednesday without a hitch. The successful test run, involving centres in Europe, South America, the US, and Australia, leaves the mission all set for its launch on 26 February.
The spacecraft’s target is Comet 67P/Churyumov-Gerasimenko (Chury), which it aims to arrive at in 2014. If all goes well, Rosetta will be the first mission to orbit a comet and to release a lander onto a comet’s nucleus. The mission will then spend two years examining this flying remnant of the Solar System’s primordial material.
The mission was originally due to launch in January 2003. But it had to be postponed after the failure a month before of a new type of Ariane-5 rocket that was set to carry the probe into space.
The delay meant Rosetta missed the launch window for its original target, Comet Wirtanen. The next opportunity to reach that comet was not for almost 200 years.
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“The bad thing [about having to switch targets] is it’s one or two years longer,” says Kathrin Altwegg, a Rosetta team member from the University of Bern in Switzerland. Rosetta would have reached Wirtanen in 2012.
Collapsible legs
Chury is also three times larger than the 1.4-kilometre-long Wirtanen, and therefore has a greater gravitational pull. This means the lander’s impact will be more forceful and so engineers have had to strengthen its three legs. This has reduced the built-in collapsibility of the legs and so the landing site will have to be much flatter than originally planned.
However, scientifically, Chury could prove to be a more interesting target than Wirtanen. Andrew Coates, a team member from University College London, UK, says it appears to have retained more of its original material – the same material that built the Solar System about 4.6 billion years ago.
“Chury seems to be more pristine,” he says. The evidence for this is that Chury looks as if it is still releasing carbon monoxide or dioxide gases, while Wirtanen is not, having presumably exhausted its supply.
Researchers will use spectrometers and cameras on both the orbiter and lander to examine the composition of Chury. The lander will also drill down up to 20 centimetres below the surface of the comet’s nucleus to retrieve samples. Rosetta will probe the nucleus’s internal structure by sending radio waves right through the comet to the lander.
‘Perverted mind’
Wednesday’s simulation was the last of 25 carried out since the mission was reconfigured. The exercise was coordinated from the European Space Operations Centre in Darmstadt, Germany, where the spacecraft will be controlled. Rosetta will launch from Kourou, French Guiana, but communication antennae in Australia, the US, and Spain will also be used.
Paolo Ferri, Rosetta’s operations manager, said the full-scale simulation included numerous failures dreamt up by the “perverted mind” of a simulations officer who “is not happy until he has seen us collapsing on the consoles “.
One of the glitches involved the craft failing to send a signal that it had separated from its launcher. This forced an antenna in Madrid to simulate spiraling around in search of the craft.
The search failed because the spacecraft had in fact gone into the wrong orbit, but an antenna in Kourou then picked up the signal. Finally, engineers were able to determine that the solar panels had deployed as planned after separation – a crucial step because of limited battery power.
“At that stage we could relax,” Ferri told New Scientist. He said the simulation showed the craft’s software and the engineers’ procedures could handle “such a dramatic, and hopefully very unlikely, multiple-failure scenario”.
