page_title: Philae (spacecraft)
section_title: Design
hierarchical_section_title: Philae (spacecraft) / Design
caption_attribution_description: English: Rosetta with Philae lander, before separation. Frame from the movie "Chasing A Comet – The Rosetta Mission".
context_page_description: Philae is a robotic European Space Agency lander that accompanied the Rosetta spacecraft until it separated to land on comet 67P/Churyumov–Gerasimenko, ten years and eight months after departing Earth. 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. After bouncing off the surface twice, Philae achieved the first-ever "soft" landing on a comet nucleus, although the lander's final, uncontrolled touchdown left it in a non-optimal location and orientation.
  Despite the landing problems, the probe's instruments obtained the first images from a comet's surface. Several of the instruments on Philae made the first direct analysis of a comet, sending back data that will be analysed to determine the composition of the surface.
  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. Mission controllers hoped that additional sunlight on the solar panels might be sufficient to reboot the lander.
context_section_description: The lander was designed to deploy from the main spacecraft body and descend from an orbit of 22.5 kilometres (14 mi) along a ballistic trajectory. It would touch down on the comet's surface at a velocity of around 1 metre per second (3.6 km/h; 2.2 mph). The legs were designed to dampen the initial impact to avoid bouncing as the comet's escape velocity is only around 1 m/s (3.6 km/h; 2.2 mph), and the impact energy was intended to drive ice screws into the surface. Philae was to then fire a harpoon into the surface at 70 m/s (250 km/h; 160 mph) to anchor itself. A thruster on top of Philae was to have fired to lessen the bounce upon impact and to reduce the recoil from harpoon firing. During the landing, the harpoons did not fire and the thruster failed to operate, leading to a multiple-contact landing.
  Communications with Earth used the Rosetta orbiter as a relay station to reduce the electrical power needed. The mission duration on the surface was planned to be at least one week, but an extended mission lasting months was considered possible.
  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 total mass is about 100 kilograms (220 lb). Its exterior is covered with solar cells for power generation.
  The Rosetta mission was originally planned to rendezvous with the comet 46P/Wirtanen. A failure in a previous Ariane 5 launch vehicle closed the launch window to reach the comet with the same rocket. It resulted in a change in target to the comet 67P/Churyumov–Gerasimenko. The larger mass of Churyumov–Gerasimenko and the resulting increased impact velocity required that the landing gear of the lander be strengthened.
caption: Rosetta and Philae
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