Philae (spacecraft)

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Philae over a comet (crop).jpg
Illustration of Philae approaching a comet
Mission type Comet lander
Operator European Space Agency
Mission duration 1–6 weeks (planned)
Spacecraft properties
Launch mass 100 kg (220 lb)[1]
Payload mass 21 kg (46 lb)[1]
Dimensions 1 × 1 × 0.8 m (3.3 × 3.3 × 2.6 ft)[1]
Power 32 watts at 3 AU[2]
Start of mission
Launch date 2 March 2004, 07:17 (2004-03-02UTC07:17Z) UTC
Rocket Ariane 5G+ V-158
Launch site Kourou ELA-3
Contractor Arianespace
67P/Churyumov–Gerasimenko lander
Landing date 12 November 2014 (planned)
APX Alpha: Alpha Proton X-ray Spectrometer
ÇIVA: Comet nucleus Infrared and Visible Analyzer
CONSERT COmet Nucleus Sounding Experiment by Radiowave Transmission
COSAC: COmetary SAmpling and Composition
MUPUS: Multi-Purpose Sensors for Surface and Subsurface Science
PTOLEMY: gas chromatograph and medium resolution mass spectrometer
ROLIS: ROsetta Lander Imaging System
ROMAP: ROsetta lander MAgnetometer and Plasma monitor
SD2: Sample and Distribution Device
SESAME: Surface Electric Sounding and Acoustic Monitoring Experiment

Philae /ˈfl/ is a robotic European Space Agency lander that accompanies the Rosetta spacecraft.[3] It is designed to land on comet 67P/Churyumov–Gerasimenko.[4][5][6] The lander is expected to achieve the first controlled touchdown on a comet nucleus. Its instruments should obtain the first images from a comet's surface and make the first in situ analysis to find out what it is made of.[7]

The lander is named after Philae Island in the Nile where an obelisk was found and used, along with the Rosetta Stone, to decipher Egyptian hieroglyphics.

As of October 2014, Philae remains attached to the Rosetta spacecraft after rendezvousing with 67P/C-G. On 15 September 2014, ESA announced Site J on the "head" of the comet as the lander's destination.[8] Philae is scheduled to detach from Rosetta on 12 November 2014 at 08:35 UTC, with a landing seven hours later.[9][10]


Philae '​s mission is to land successfully on the surface of a comet, and transmit data from the surface about the comet's composition. Unlike the Deep Impact probe, which by design struck comet Tempel 1's nucleus on 4 July 2005, Philae is not an impactor. Some of the instruments and the lander were used for the first time as autonomous systems during the Mars flyby on 25 February 2007. ÇIVA, the camera system, returned some images while the Rosetta instruments were powered down; ROMAP took measurements of the Martian magnetosphere. Most of the other instruments need contact with the surface for analysis and stayed offline during the flyby. An optimistic estimate of mission length is "four to five months".[11]

Scientific goals[edit]

The scientific goals of the mission focus on "elemental, isotopic, molecular and mineralogical composition of the cometary material, the characterization of physical properties of the surface and subsurface material, the large-scale structure and the magnetic and plasma environment of the nucleus."[12]


Rosetta and Philae

The lander is designed to deploy from the main spacecraft body and descend from an orbit of 22.5 kilometres (14 mi) along a ballistic trajectory.[13] It will touch down on the comet's surface at a velocity of around 1 metre per second (3 ft/s).[14] Upon contact it will deploy two harpoons to anchor itself to the surface, and the legs are designed to dampen the initial impact to avoid bouncing as the comet's escape velocity is only around 0.5 m/s (1.1 mph; 1.8 km/h).[15]

Communications with Earth will use the orbiter spacecraft as a relay station to reduce the electrical power needed. The mission duration on the surface is planned to be at least one week, but an extended mission lasting months is 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 "hood" is covered with solar cells for power generation.[5]

It 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. It necessitated a change in target to the comet 67P/Churyumov–Gerasimenko. The larger comet mass and the resulting increased impact velocity made modification of the landing gear necessary.[clarification needed] Besides the changes made to launch time and target, the mission profile remained unchanged.[4]

Spacecraft component Mass[12]:208
Thermal Control System 3.9 kg (8.6 lb)
Power System 12.2 kg (27 lb)
Active Descent System 4.1 kg (9.0 lb)
Flywheel 2.9 kg (6.4 lb)
Landing Gear 10 kg (22 lb)
Anchoring System 1.4 kg (3.1 lb)
Central Data Management System 2.9 kg (6.4 lb)
Telecommunications System 2.4 kg (5.3 lb)
Common Electronics Box 9.8 kg (22 lb)
Mechanical Support System, Harness, balancing mass 3.6 kg (7.9 lb)
Scientific payload 26.7 kg (59 lb)
Sum 97.9 kg (216 lb)

Power management[edit]

Philae power management has been planned for two phases. In the first phase, the lander will operate solely on battery power. In the second phase, "it will run on backup batteries recharged by solar cells".[11]


The science payload of the lander consists of ten instruments massing 26.7 kilograms (59 lb), making up nearly one-third of the mass of the lander.[12]

  • APXS (Alpha Proton X-ray Spectrometer) APXS, it detects alpha particles and X-rays, which provide information on the elemental composition of the comet's surface.[16] The instrument is an improved version of the APXS of the Mars Pathfinder.
  • COSAC (COmetary SAmpling and Composition), the combined gas chromatograph and time-of-flight mass spectrometer perform analysis of soil samples and determine the content of volatile components.[17][18]
  • Ptolemy is an instrument measuring stable isotope ratios of key volatiles on the comet's nucleus.[19][20]
  • ÇIVA (Comet Nucleus Infrared and Visible Analyzer) is a group of six identical micro-cameras that take panoramic pictures of the surface. Each camera has a 1024×1024 pixel CCD detector.[21] A spectrometer studies the composition, texture and albedo (reflectivity) of samples collected from the surface.[22]
  • ROLIS (Rosetta Lander Imaging System) is a CCD camera that will obtain high-resolution images during descent and stereo panoramic images of areas sampled by other instruments.[23] The CCD detector consists of 1024×1024 pixels.[24]
  • CONSERT (COmet Nucleus Sounding Experiment by Radiowave Transmission). The CONSERT radar will perform tomography of the nucleus by measuring electromagnetic wave propagation from Rosetta orbiter through the nucleus that are returned by a transponder on the Philae lander in order to determine the comet's internal structure.[25][26]
  • MUPUS (MUlti-PUrpose Sensors for Surface and Sub-Surface Science) uses sensors on the lander to measure the density, thermal and mechanical properties of the surface.[27]
  • ROMAP (Rosetta Lander Magnetometer and Plasma Monitor) is a magnetometer and plasma monitor to study the nucleus' magnetic field and its interactions with the solar wind.[28]
  • SESAME (Surface Electric Sounding and Acoustic Monitoring Experiments) will use three instruments to measure properties of the comet's outer layers. The Cometary Acoustic Sounding Surface Experiment (CASSE) measures the way in which sound travels through the surface. The Permittivity Probe (PP) investigates its electrical characteristics, and the Dust Impact Monitor (DIM) measures dust falling back to the surface.[29]
  • SD2 (Drill, Sample, and Distribution subsystem) Obtains soil samples from the comet at depths of 0 to 230 millimetres (0.0 to 9.1 in) and distributes them to the Ptolemy, COSAC, and ÇIVA subsystems for analyses.[30] The system contains four types of subsystems: drill, carousel, ovens, and volume checker.[31] There are a total of 26 platinum ovens to heat samples—10 medium temperature 180 °C (356 °F) and 16 high temperature 800 °C (1,470 °F)—and one oven to clear the drill bit for reuse.[32]

International contributions[edit]

The Austrian Space Research Institute developed the lander's anchor and two sensors within MUPUS, which are integrated into the anchor tips. They indicate the temperature variations and the shock acceleration.
The Finnish Meteorological Institute provided the Memory of the Command, Data and Management System (CDMS) and the Permittivity Probe (PP).
The French Space Agency together with some scientific laboratories (IAS, SA, LPG, LISA) provided the system's overall engineering, radiocommunications, battery assembly, CONSERT, CIVA and the ground segment (overall engineering and development/operation of the Scientific Operation & Navigation Centre).
The German Space Agency (DLR) has provided the structure, thermal subsystem, flywheel, the Active Descent System (procured by DLR but made in Switzerland), ROLIS, downward-looking camera, SESAME, acoustic sounding and seismic instrument for Philae. It has also managed the project and did the level product assurance. The University of Munster built MUPUS (it was designed and built in Space Research Centre of Polish Academy of Sciences [33]) and the Braunschweig University of Technology the ROMAP instrument. The Max Planck Institute for Solar System Research made the payload engineering, eject mechanism, landing gear, anchoring harpoon, central computer, COSAC, APXS and other subsystems.
The Command and Data Management Subsystem (CDMS) designed in the Wigner Research Centre for Physics of the Hungarian Academy of Sciences. The Power Subsystem (PSS) designed in the Department of Broadband Infocommunications and Electromagnetic Theory at Budapest University of Technology and Economics. CDMS is the fault tolerant central computer of the lander, while PSS assures that the power coming from the batteries and solar arrays are properly handled, controls battery charging and manages the onboard power distribution.
The Italian Space Agency (ASI) has a significant role in Philae. It has provided the SD2 instrument and the Photo Voltaic Assembly. The industrial contractors are respectively Tecnospazio spA and Galileo Avionica spA.
Space Technology Ireland Ltd. at Maynooth University has designed, constructed and tested the Electrical Support System Processor Unit (ESS) for the Rosetta mission. ESS stores, transmits and provides decoding for the command streams passing from the spacecraft to the lander and handles the data streams coming back from the scientific experiments on the lander to the spacecraft.
The Space Research Centre of the Polish Academy of Sciences built MUPUS.[33]
United Kingdom 
The Open University and the Rutherford Appleton Laboratory (RAL) have developed PTOLEMY. RAL has also constructed the blankets that keep the lander warm throughout its mission. Surrey Satellites Technology Ltd. (SSTL) constructed the momentum wheel for the lander. It stabilises the module during the descent and landing phases.


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External links[edit]

Further reading