Despite a new trajectory for Rosetta and a reduction of the distance between the orbiter and Comet 67P/Churyumov-Gerasimenko from 200 to 180 kilometres, contact with the Philae lander remains irregular and short. After the initial contact on 13 June 2015, Philae has reported to the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Lander Control Center (LCC) in Cologne a total of six times.
The team at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) received data from the Philae lander for the third time on 19 June 2015. Between 15:20 and 15:39 CEST, Philae sent 185 data packets.
The Philae lander reported back on 14 June 2015. From 23:22 to 23:26 CEST, the lander sent some data packets that are now being evaluated at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). "But this time, the connection to the lander was relatively unstable," says DLR Philae Lander Project Leader Stephan Ulamec.
The Philae lander has reported back on 13 June 2015 at 22:28 (CEST), coming out of hibernation and sending the first data to Earth. More than 300 data packets have been analysed by the team at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Lander Control Center: "Philae is doing very well – it has an operating temperature of minus 35 degrees Celsius and has 24 watts of power available," explains DLR’s Philae Project Manager, Stephan Ulamec. "The lander is ready for operations." Philae 'spoke' for 85 seconds with its team on ground in its first contact since it went into hibernation.
On 15 November 2014 at 01:15 CET, Philae's battery was exhausted and, after nearly 60 hours of operation on Comet 67P/Churyumov-Gerasimenko, the lander went into hibernation – in an unexpected place. Philae 'bounced' several times before landing in its current location, and its exact position has still not been determined.
Comets eject gas and dust into space. Primarily, this takes place on the areas of the comet's surface exposed to direct sunlight. In mid-March, from a distance of 75 kilometres, the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) on board the Rosetta orbiter acquired images of an extraordinary phenomenon occurring on Comet 67P/Churyumov-Gerasimenko.
Although from 28 March 2015, following difficulties with its star trackers and navigation system, the Rosetta orbiter is now following a new and more distant trajectory around Comet 67P/Churyumov-Gerasimenko, the team at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Lander Control Center (LCC) will begin listening again for signals from the Philae lander at 02:00 CET on 12 April 2015.
Perhaps it is still too cold for the Philae lander to wake up on Comet 67P/Churyumov-Gerasimenko. Maybe its power resources are not yet sufficient to send a signal to the team at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Lander Control Center.
It would be very lucky if a signal were to be received from Rosetta's Philae lander at 05:00 CET on 12 March 2015. The lander finally came to rest in a rather shaded location on Comet 67P/Churyumov-Gerasimenko and it needs to receive sufficient energy before it can wake up and begin communicating.
On 14 February 2015, the Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS) on the Rosetta spacecraft observed the surface of comet 67P Churyumov-Gerasimenko with the Sun directly behind it, so the only shadow seen in the image is that of the photographer, the orbiter itself.
Comet 67P/Churyumov-Gerasimenko could lose up to 20 metres of surface material from its previously unilluminated south side when it heats up, starting in May 2015. The increasing heat as the comet approaches the Sun will trigger this 'diet', during which gases and solid materials will be ejected into space.
The Lander Control Center (LCC) at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) is quiet. While the Philae lander is hibernating on the surface of Comet 67P/Churyumov-Gerasimenko, the control room team are able to take a break. Philae' s battery finally ran out at 01:36 CET on 15 November 2014, following a triple landing and more than 56 hours of scientific work.
It is still early days for the scientists involved in evaluating data that the 21 instruments on board the Rosetta spacecraft and its Philae lander have transmitted back to Earth. But preliminary results from seven of the 11 instruments on the Rosetta orbiter have been published in a special edition of the journal Science.
Just three kilometres from Comet 67P/Churyumov-Gerasimenko, the ROsetta Lander Imaging System (ROLIS) acquired images of the 'head' and underlying 'body' of Comet 67P. Immediately below is the planned landing site, Agilkia; in the top right of the field of view, one of the landing gear feet can be seen as the camera on the underside of the lander approaches the comet's surface at walking pace.
A short but significant 'thud' was heard by the Cometary Acoustic Surface Sounding Experiment (CASSE) as Philae made its first touchdown on Comet 67P/Churyumov-Gerasimenko. The two-second recording from space is the very first of the contact between a man-made object with a comet upon landing.
The MUPUS instrument, one of 10 experiments on the Philae lander that touched down on comet 67P/Churyumov-Gerasimenko encountered very hard material with a temperature of about minus 170 degrees Celsius – probably rich in ice.
Before going into hibernation at 01:36 CET on 15 November 2014, the Philae lander was able to conduct some work using power supplied by its primary battery. With its 10 instruments, the mini laboratory sniffed the atmosphere, drilled, hammered and studied Comet 67P/ Churyumov-Gerasimenko while over 500 million kilometres from Earth.
Update – the Philae lander entered sleep mode at 01:36 CET on 15 November 2014.
The Philae lander performed about 56 hours of continuous scientific measurements on the surface of Comet 67P, but by 01:15 CET on 15 November the energy state of the lander became so low that the engineers assumed that Philae would go into sleep mode during the night.
Not only was it the first ever landing on a comet – it was also the second and third. Since 18:32 CET on 12 November 2014, the Philae lander has been on the surface of Comet 67P/Churyumov-Gerasimenko, performing experiments and returning data.
Rosetta's lander Philae is safely on the surface of Comet 67P/Churyumov-Gerasimenko, as these first two CIVA images confirm.