Philae remained attached to the
Rosetta spacecraft after rendezvousing with Churyumov–Gerasimenko on 6 August 2014. On 15 September 2014, ESA announced "" on the smaller lobe of the comet as the lander's destination. Following an ESA public contest in October 2014, was renamed
Agilkia in honour of
Agilkia Island. A series of four
go/no-go checks were performed on 11–12 November 2014. One of the final tests before detachment from
Rosetta showed that the lander's
cold-gas thruster was not working correctly, but the "go" was given anyway, as it could not be repaired.
Philae detached from
Rosetta on 12 November 2014 at 08:35 UTC
SCET.
Landing events '' signal received at
ESOC in Darmstadt, Germany (20 January 2014)
Philae landing signal was received by Earth communication stations at 16:03 UTC after a 28-minute delay. Unknown to mission scientists at that time, the lander had bounced. It began performing scientific measurements while slowly moving away from the comet and coming back down, confusing the science team. Further analysis showed that it bounced twice. The probe rebounded off the comet's surface at and rose to an altitude of approximately . After detecting the touchdown,
Philae reaction wheel was automatically powered off, resulting in its momentum being transferred back into the lander. This caused the vehicle to begin rotating every 13 seconds.
Philae touched down a second time at 17:25:26 UTC SCET and rebounded at . Its final location was determined initially by analysis of data from
CONSERT in combination with the comet shape model based on images from the
Rosetta orbiter, and later precisely by direct imaging from
Rosetta. that the harpoons had not deployed, and that the thruster had not fired. The harpoon propulsion system contained 0.3 grams of
nitrocellulose, which was shown by
Copenhagen Suborbitals in 2013 to be unreliable in a vacuum.
Operations and communication loss The primary battery was designed to power the instruments for about 60 hours. On the morning of 14 November 2014, the battery charge was estimated to be only enough for continuing operations for the remainder of the day. After first obtaining data from instruments whose operation did not require mechanical movement, comprising about 80% of the planned initial science observations, both the MUPUS soil penetrator and the SD2 drill were commanded to deploy. Subsequently, MUPUS data as well as COSAC and Ptolemy data were returned. A final set of CONSERT data was also downlinked towards the end of operations. During the evening's transmission session,
Philae was raised by and its body rotated 35 degrees to more favourably position the largest solar panel to capture the most sunlight in the future. Shortly afterwards, electrical power dwindled rapidly and all instruments were forced to shut down. The downlink rate slowed to a trickle before coming to a stop. Contact was lost on 15 November at 00:36 UTC. The
German Aerospace Center's lander manager
Stephan Ulamec stated:
Instrument results Data from the SESAME instrument determined that, rather than being "soft and fluffy" as expected,
Philae first touchdown site held a large amount of water ice under a layer of granular material about deep. It found that the mechanical strength of the ice was high and that cometary activity in that region was low. At the final landing site, the MUPUS instrument was unable to hammer very far into the comet's surface, despite power being gradually increased. This area was determined to have the consistency of solid ice or
pumice. In the atmosphere of the comet, the COSAC instrument detected the presence of molecules containing carbon and hydrogen. Soil elements could not be assessed, because the lander was unable to drill into the comet surface, likely due to hard ice. The SD2 drill went through the necessary steps to deliver a surface sample to the COSAC instrument, Upon
Philae first touchdown on the comet's surface, COSAC measured material at the bottom of the vehicle, which was disturbed by the landing, while the Ptolemy instrument measured material at the top of the vehicle. Sixteen
organic compounds were detected, four of which were seen for the first time on a comet, including
acetamide,
acetone,
methyl isocyanate and
propionaldehyde.
Reawakening and subsequent loss of communication in March 2015 as imaged by
Rosetta in true colour On 13 June 2015 at 20:28 UTC, ground controllers received an 85-second transmission from
Philae, forwarded by
Rosetta, indicating that the lander was in good health and had sufficiently recharged its batteries to come out of
safe mode.
Philae sent historical data indicating that although it had been operating earlier than 13 June 2015, it had been unable to contact
Rosetta before that date. The first signal was received on the ground from
Rosetta at 13:37 UTC, while a second signal was received at 13:54 UTC. These contacts lasted about two minutes each and delivered additional status data. There were two opportunities for contact between the two spacecraft each Earth day, but their duration and quality depended on the orientation of the transmitting antenna on
Philae and the location of
Rosetta along its trajectory around the comet. Similarly, as the comet rotated,
Philae was not always in sunlight and thus not always generating enough power via its solar panels to receive and transmit signals. ESA controllers continued to try to establish a stable contact duration of at least 50 minutes. ,
Philae key remaining experiment was to drill into the comet's surface to determine its chemical composition. Ground controllers sent commands to power up the
CONSERT radar instrument on 5 July 2015, but received no immediate response from the lander. Confirmation was eventually received on 9 July, when the lander transmitted measurement data from the instrument. Immediately after its reawakening, housekeeping data suggested that the lander's systems were healthy, and mission control uploaded commands for
Rosetta to establish a new orbit and
nadir so as to optimize communications, diagnostics, and enable new science investigations with
Philae. However, controllers had difficulties establishing a stable communications connection with the lander. The situation was not helped by the need to keep
Rosetta at a greater and safer distance from the comet as it became more active. The last communication was on 9 July 2015, Subsequently,
Philae failed to respond to further commands, and by January 2016, controllers acknowledged no further communications were likely. On 27 July 2016, at 09:00
UTC, ESA switched off the Electrical Support System Processor Unit (ESS) onboard
Rosetta, making further communications with
Philae impossible.
Location The lander was located on 2 September 2016 by the narrow-angle camera aboard
Rosetta as it was slowly making its descent to the comet. The search area was narrowed down to the most promising candidate, which was confirmed by a picture taken at a distance of , clearly showing the lander. The lander sits on its side wedged into a dark crevice of the comet, explaining the lack of electrical power and proper communication with the probe. Knowing its exact location provides information needed to put
Philae two days of science into proper context. == Design ==