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New contact with Philae as Rosetta switches on experiment

Paul Sutherland, Feature writer
Jul 10, 2015, 17:08 UTC

Sen—The Rosetta rollercoaster brought some good news about little lander Philae today when mission scientists reported that they had made contact again with the probe sitting on the surface of Comet 67P/Churyumov-Gerasimenko.

It happened on the second attempt made by the lander control team to turn on the power to an experiment called CONSERT (the COmet Nucleus Sounding Experiment by Radiowave Transmission) which has its own aerial on Philae.

A previous attempt to do this, on Sunday July 5, was unsuccessful. But this time, Philae communicated again with its orbiting mothership from 17.45 to 18.07 UTC, and also sent some data from the instrument. Furthermore, the signal was completely stable for 12 minutes, though erratic subsequently.

The European Space Agency's Rosetta mission team are elated by this latest promising development in the mission’s story. Having woken up and phoned home, to everyone’s delight, on June 13, after seven months of silence, Philae then made only sporadic contact and nothing had been heard from it again since June 24.

Rosetta Chief Scientist Matt Taylor told Sen: “We are glad to hear from Philae and hope to work out how to ensure a capability for science, which is not yet there. At the same time we must consider lander science and fit lander communications around that.”

Communications specialists on the team at the German Aerospace Center (DLR) will now be looking closely at the details of how Philae reported in and the nature of its signals to see if that can help them improve the situation further.

Reporting the latest development today, Koen Geurts, a member of the lander control team at DLR Cologne, said in a statement: “This sign of life from Philae proves to us that at least one of the lander’s communication units remains operational and receives our commands.” He added: “We never gave up on Philae and remained optimistic.”

One reason why communication with Philae can never be continuous anyway is that it has to talk to mission control via Rosetta, acting as a relay, and the mothership is often below the horizon on the other side of the comet and so unable to establish a radio link.

The intermittent nature of communications since Philae’s revival, when Rosetta should have been in the right place, has been a puzzle to the team. Rosetta Chief Scientist told Sen earlier this week, before last night’s attempt at contact, that if it failed they were preparing a further approach to try for a signal. That was to involve getting Rosetta into orbital positions that would have exactly matched the geometry between it and Philae when earlier signals were received.

Data received from Philae on June 24 did not suggest that the lander had suffered any technical problems, according to the team. They now hope that, being closer to the Sun as the comet nears perihelion next month, the lander will be able to charge its batteries and function again, carrying out science on 67P. Its internal temperature is thought to be around 0° C now which should be plenty to keep it healthy.

While his colleagues were evaluating the latest data from Philae, Geurts added in his statement: “We can already see that the CONSERT instrument was successfully activated by the command we sent on 9 July. We do not yet have an explanation for why the lander has communicated now, but not over the past few days.”

However, the fact that Philae obeyed Rosetta’s command and switched on CONSERT last night gives the team hope because it suggests the lander survived the harsh conditions during its long hibernation and is ready to respond to further commands if it receives them. Guerts said: “This is extremely good news for us.”