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Rosetta team propose ending mission by landing on comet

Paul Sutherland, Feature writer
May 29, 2015, 12:15 UTC

Sen—Rosetta space scientists put forward a daring proposal this week to end the probe’s mission by sending it to land on the comet it has been accompanying through the Solar System since August 2014.

The European Space Agency (ESA) spacecraft is still weeks away from the exciting climax of its mission as Comet 67P/Churyumov-Gerasimenko grows ever more active on its journey closer to the Sun. But the Rosetta team are busy planning ahead.

Comet 67P reaches perihelion—its closest approach to the Sun—on Aug. 13, 2015, at a distance from it of 186 million km (116 million miles) after which it will start to head further out into the Solar System again on its 6.5-year orbit.

The mission is currently set to end in December 2015, after which Rosetta could simply be switched off as it continues to orbit the comet, and the mission team disperse to work on new projects. But for several months now a plan has been quietly hatched to see the craft go out with a bang by being brought down to a collision with 67P.

The dramatic grand finale was officially put forward to ESA this week by project scientist Matt Taylor. It is expected that the ESA science committees that decide such things will have an answer by the end of next month. An extension to the mission would require extra funding to keep the Rosetta operations team together, but supporters of the move believe the extra science gained would be invaluable.

It would see the spacecraft brought gradually closer to the comet in a slowly spiralling orbit that would allow its cameras and instruments to gain ever more detailed views and measurements of the twin-lobed icy body. Then eventually—probably in September 2016—it would collide with the comet, bringing the mission to an end.

Of course, Rosetta has already attempted one landing on Comet 67P when it despatched its companion probe Philae, which bounced twice before settling in a shaded spot where it swiftly lost power—though only after achieving its full range of initial experiments. The ESA team are still attempting to resurrect the tiny lander, hoping that the comet’s changing orientation and proximity to the Sun will give it enough sunlight to recharge its batteries.

Matt told Sen: “Our mission was due to end at the end of this year. We have simply asked to extend to September next year, by which time the energy from the Sun to the solar panels starts to drop again. Plus we will have a solar conjunction (when the Sun lies between Earth and Rosetta), so data rates will be reduced. Also, we have limited fuel, which is sufficient to take us comfortably up to the point, but not much further.”

He added: “If we just left Rosetta as is, we would need to put it into hibernation again, for longer, as it is now in the same orbit as the comet. We would then have to go through the difficult process of 1) putting it into hibernation and then 2) getting it out of hibernation again. Then we have the issues of minimal fuel etc. The spacecraft would remain in a similar orbit as the comet for years, dependent on whether the comet breaks up, etc.”

Matt told Sen that landing Rosetta would produce some great science. He told us: “The proposal to put the probe on the comet’s surface provides us with unique, close comet observations that we could not have if we don’t do this. Also, I feel from a ‘personal’ perspective, there is something rather fitting in putting Rosetta down on the surface, re-uniting it with Philae.”

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How Rosetta might look as it moves in ever closer to the comet. Image credit: DLR (CC-BY 3.0)

He added: “We have a few more hurdles to jump through—higher level science committees—but we will know whether we have it (the go-ahead) by end of June. What happens then is that we can start planning into that period. We will have a science meeting in June in Rome, and will likely discuss such plans in the case that we do get extended.”

The cost of extending the mission is not clear at present. Matt said: “Costs are not my department, but we simply want to carry on at the level we have now.”

Meanwhile, mission scientists are about to begin their fourth series of attempts to re-establish contact with Philae, following earlier unsuccessful efforts in March, April and earlier in May. From tomorrow, May 30, Rosetta will again try to pick up a signal from its companion probe.

The efforts are being managed by the French national centre for space studies, CNES, in Toulouse. CNES’ Science Operation and Navigation Centre (SONC) is busy working out the best times when Philae’s solar panels might get sufficient sunlight to produce energy to wake it up.

Éric Jurdo, of SONC, said on the CNES website on Thursday that, thanks to data from various instruments on Rosetta and the lander before it lost power, “we know with an accuracy of less than 50 metres the final landing point of Philae. We also know how the undercarriage is oriented relative to the surface.”

The SONC team has also been planning for the moment that contact is made again with Philae, so that command sequences can be sent at once to put it to work again while it has power.