Comet-chaser fires up its Philae minion

The Philae lander, which is piggybacking on a comet, is back in business. (German Aerospace Centre)

The Philae lander, which is piggybacking on a comet, is back in business. (German Aerospace Centre)

The Rosetta spacecraft was set to swoop into a closer orbit around comet 67P/Churyumov-Gerasimenko this week to help the mothership talk to its Philae lander, which emerged from a seven-month hibernation last Saturday.

Changing Rosetta’s orbit to bring the spacecraft within 180km of the comet’s surface should give Rosetta stronger and longer communication links with the lander, and allow scientists to send commands to the robot.

The lander made its first brief contact with Rosetta on Saturday last week, when the little robot beamed up 300 of the 8 000 packets of housekeeping data it had saved on board. On Sunday night, the lander made contact again and scientists at the French Space Agency CNES declared it was now “completely awake”.

The signals are the first to come from the washing-machine-sized Philae since November last year, when its batteries ran out and the probe fell silent. The lander came out of standby mode and used its transmitter to call home after its solar panels received enough sunlight to power the systems up.

The lander is expected to gain more power over the coming weeks and months as the comet gets closer to the sun.

Battery recharge
“Sunday’s data are telling us that Philae is at -5?C, and that is really good news, because it is warm enough to start recharging the batteries,” said Stephan Ulamec, Philae lander manager at the German Aerospace Centre in Darmstadt.

“It’s an indication that in the coming weeks and months we’ll be able to recharge the lander and do more demanding science with the instruments,” he said.

The Philae team has drawn up a list of operations that will be sent to the lander when it has the power to perform the tasks.
The first will be simple actions, such as taking the outside temperature and more magnetic measurements.

With a little more power, Philae will take pictures of its surroundings, to see whether the terrain has changed since it landed. Next, the lander will try to “sniff” the environment for volatile chemicals.

“Most demanding, but most interesting, will be getting a sample with the drill and investigating it with instruments like Ptolemy, but that’s not something we’ll do soon, because it needs fully recharged batteries,” Ulamec said.

The Ptolemy instrument can take samples drilled from the comet’s surface and infer their composition by analysing gases given off when the material is baked.

Dust from the comet has probably already been swept into the ovens, and this could be analysed if Philae can muster enough power to turn the ovens on.

‘Exciting time’
Monica Grady, professor of planetary sciences at the Open University, said: “We are so happy Philae has woken up. It’s a really exciting time.”

Before deciding whether to use Ptolemy’s ovens, mission controllers must find out whether Philae’s drill can still reach the comet’s surface.

“We don’t know yet whether the drill can deliver anything. It was supposed to drill vertically down, but as far as we’re aware, Philae is on its side,” Grady said.

The Rosetta spacecraft flew more than six billion kilometres on its 11-year mission to rendezvous with the comet, which orbits the sun at 135 000km/h.

The Philae lander touched down on the comet seven months ago and, after bouncing a bit, came to rest against a cliff face, where much of the craft was in shadow.

The comet is now 215-million kilometres from the sun and 305-million kilometres from Earth. – © Guardian News & Media 2015

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