Philae ends hibernation after 211 days; mission team thrilled
It seems Philae have had enough of hibernation time as on June 13, ESA’s comet lander woke up from 211 days of sleep and sent back more than 300 packets of data at 22:28 CEST.
Philae went into hibernation on Comet 67P/Churyumov–Gerasimenko after its initial batteries expired and owing to the lack of enough sunlight, which has been attributed to its odd landing position and oblique angle hidden from the Sun.
Philae last contacted Earth on November 14 as on the very next day at at 00:36 GMT, the lander shutdown after completing its main science operations sequence on the comet when the primary battery expired as expected after about 60 hours. But the lander never woke up because it never had enough sunlight to power its batteries.
According to ESA, on the evening of June 13, a weak but solid radio link between Rosetta and the lander was finally established for 85 seconds. More than 300 ‘packets’ – 663 kbits – of lander housekeeping telemetry were received. This information had been stored on board at an as-yet-to-be determined time in the past, as much as several days to a few weeks, so does not necessarily reflect the lander’s current status.
Rosetta then relayed the signal to ESA’s European Space Operations Centre, ESOC, in Darmstadt, Germany, at 20:28 GMT.
“Philae is doing very well: It has an operating temperature of -35ºC and has 24 Watts available,” explains DLR Philae Project Manager Dr. Stephan Ulamec. “The lander is ready for operations.”
ESA received a second, smaller burst of lander data on Sunday, 14 June, at about 21:26 GMT, lasting just a few seconds. These data were confirmed to give the current status, showing the lander’s internal temperature had already risen to –5ºC.
Now the scientists are waiting for the next contact. There are still more than 8000 data packets in Philae’s mass memory which will give the DLR team information on what happened to the lander in the past few days on Comet 67P/Churyumov-Gerasimenko.
“We are still examining the housekeeping information at the Lander Control Centre in the DLR German Aerospace Center’s establishment in Cologne, but we can already tell that all lander subsystems are working nominally, with no apparent degradation after more than half a year hiding out on the comet’s frozen surface,” says DLR’s Stephan Ulamec, Philae Lander Project Manager.
Engineers at the Lander Control Centre have determined that Philae is already being exposed to sufficient sunlight to heat it to an acceptable operating temperature and to generate electricity.
“Power levels increase during the local ‘comet day’ – the part of the about-12 hour comet rotation when Philae is in sunlight – from 13 W at comet sunrise to above 24 W,” notes ESA’s Patrick Martin, Rosetta Mission Manager. “It needs at least 19 W to switch on the transmitter.”
The telemetry downloaded covered the lander’s status for a full night–day cycle of the comet, which is helping ground teams to understand how the Sun is shining on the lander. The solar panels appear to be receiving power for over 135 minutes in each illumination period.
“While the information we have is very preliminary, it appears that the lander is in as good a condition as we could have hoped,” says Dr Ulamec.