ESA tries UPLOADING PATCH to Philae lander to fix radios

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German Aerospace Center depiction of Philae on Comet 67/P

The Philae lander may well be alive and mostly well upon Comet 67P/Churyumov-Gerasimenko, but the European Space Agency (ESA) is trying to patch its radio transmitters to overcome communications problems.

That's the gist, as your correspondent sees it, of a lengthy “behind the scenes” post from ESA boffins explaining their attempts to contact the lander.

Readers will remember that the lander touched down in November 2014 after bouncing a few times, but seems to have settled in a spot where it struggles to see enough of the Sun to charge its batteries. The lander sent home a few hours of glorious data, but then put itself to sleep for several months.

That slumber ended in June when the lander made contact with the Rosetta orbiter before again going quiet.

The ESA's new post reveals that contact has since been made with the lander on 9 July, yielding just 246 packets, each comprising 141 16-bit words for a total of 2,256 bits of data. Which is great news because if contact is possible, it suggests that the radio was working well enough to send the data. Some of Philae's other instruments may yet be working and gathering information about just what it's like on Comet 67P.

Sadly the 9 July contact also yielded bad news, as it took more than 35 minutes to establish the two-way link between the Rosetta orbiter and the Philae lander. That's not good because, as the post explains, “on-board software should switch on one of Philae’s two transmitters as soon as a signal is received, in order to establish the two-way link. However, if the link is not made within three minutes and signals continue to be received from Rosetta, the first transmitter unit is declared faulty and the software switches on the other one.”

Analysis of how much current each receiver is using suggests both may well be experiencing short circuits, but the primary receiver (TX1) is seen as more likely to be healthy than TX2.

The ESA is therefore trying to send a patch to Philae so that instead of trying to activate TX2 when TX1 times out, the lander keeps trying to make TX1 work.

The Rosetta orbiter has been trying to upload the patch to Philae, but recent weeks have been a lousy time to try talking to Philae, because 67P has just rounded the Sun and is therefore a mess of dust and other debris. During early August Rosetta therefore backed off to keep itself safe, so between the extra distance and the vicissitudes of radio communication through a comet's corona, the ESA has no idea if the patch was received or installed.

The orbiter has since, in late August, used an orbit that gave it a decent chance of reaching and hearing from Philae, but the ESA says no contact was made. While that's not a good sign, the post says ESA boffins continue to pore over the data gathered during Philae's brief contacts, in search of clues that will help them to re-establish contact. If even a single packet makes it out, that's a bonus as the lander wasn't expected to survive 67P's closest approach to the Sun, which took place on August 13th.

The post says Philae has enough power to survive until late 2015, so attempts to contact the lander will continue until all hope is extinguished, a fitting effort given the amazing feats of science and engineering that saw humanity land a functioning robot on a moving comet. ®

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