Philae (/ˈfaɪliː/[6] or /ˈfiːleɪ/[7]) was a robotic European Space Agency lander that accompanied the Rosetta spacecraft[8][9] until it separated to land on comet 67P/Churyumov–Gerasimenko, ten years and eight months after departing Earth.

[10][11][12] On 12 November 2014, Philae touched down on the comet, but it bounced when its anchoring harpoons failed to deploy and a thruster designed to hold the probe to the surface did not fire.

[13] After bouncing off the surface twice, Philae achieved the first-ever "soft" (nondestructive) landing on a comet nucleus,[14][15][16] although the lander's final, uncontrolled touchdown left it in a non-optimal location and orientation.

[18] Several of the instruments on Philae made the first in-situ analysis of a comet nucleus, sending back data regarding the composition of the surface and outgassing from the subsurface.

[20] On 15 November 2014 Philae entered safe mode, or hibernation, after its batteries ran down due to reduced sunlight and an off-nominal spacecraft orientation at the crash site.

[26] The lander is named after the Philae obelisk, which bears a bilingual inscription and was used along with the Rosetta Stone to decipher Egyptian hieroglyphs.

Philae was monitored and operated from DLR's Lander Control Center in Cologne, Germany, supported by the CNES' SONC in Toulouse, France.

The Rosetta spacecraft and Philae lander were launched on an Ariane 5G+ rocket from French Guiana on 2 March 2004, 07:17 UTC, and travelled for 3,907 days (10.7 years) to Churyumov–Gerasimenko.

Unlike the Deep Impact probe, which by design struck comet Tempel 1's nucleus on 4 July 2005, Philae is not an impactor.

[39] During this first bounce, at 16:20 UTC SCET, the lander is thought to have struck a surface prominence, which slowed its rotation to once every 24 seconds and sent the craft tumbling.

[39] It sits in rough terrain, apparently in the shadow of a nearby cliff or crater wall, and is canted at an angle of around 30 degrees, but is otherwise undamaged.

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.

During the evening's transmission session, Philae was raised by 4 centimetres (1.6 in) and its body rotated 35 degrees to more favourably position the largest solar panel to capture the most sunlight in the future.

[53]Data from the SESAME instrument determined that, rather than being "soft and fluffy" as expected, Philae's first touchdown site held a large amount of water ice under a layer of granular material about 25 cm (9.8 in) deep.

[60][61][62] 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.

[65] 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.

[65] Had Philae landed at the planned site of Agilkia in November 2014, its mission would probably have ended in March 2015 due to the higher temperatures of that location as solar heating increased.

[66] As of June 2015[update], Philae's key remaining experiment was to drill into the comet's surface to determine its chemical composition.

[68] 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.

[74] 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.

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.

[citation needed] The main structure of the lander is made from carbon fiber, shaped into a plate maintaining mechanical stability, a platform for the science instruments, and a hexagonal "sandwich" to connect all the parts.

The solar panels cover 2.2 square metres (24 sq ft) and were designed to deliver up to 32 watts at a distance of 3 AU from the Sun.

[20] This occurred primarily at the site of Philae's second touchdown onto the 67P/Churyumov–Gerasimenko, where the spacecraft successfully produced four distinct surface contacts on two adjoining cometary boulders.

[140] Online comic author Randall Munroe wrote a live updating strip on his website xkcd on the day of the landing.