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Philae

NSSDCA ID: 2004-006C

Description

Philae is the landing craft of the Rosetta mission, which touched down on Comet 67P/Churyumov-Gerasimenko on 12 November 2014. The scientific objectives are to determine the physical properties of the comet's surface and subsurface and their chemical, mineralogical and isotopic composition. This information will be used in tandem with the data returned by the Rosetta orbiter to characterize the comet.

Spacecraft and Subsystems

The Philae spacecraft is a partial hexagonal cylinder, approximately 1 meter across and 80 cm high, open on one end, supported on a long squat tripod and consists of a baseplate, experiment platform and hood. The structure is made of high modulus carbonfiber with an aluminum coating in a polygonal sandwich construction. The landing gear consists of a central telescopic tube connecting lift and torque mechanism located in the cavity of the lander's body connected at the lower end by a kardanic joint to the center of the tripod. The three lander legs are equipped with shock absorbers to inhibit bouncing in the low gravity. Push-down and hold-down thrusters are used to accelerate descent and impede rebound after touchdown. Twin harpoons connected to tethers will be fired into the surface of the comet to anchor the lander. Power will be provided by low intensity, low temperature GaAs solar cells mounted on the top panel of the lander hood and a 970 Whr and 110 Whr battery. The lander will communicate with the Rosetta spacecraft via a 1 W S-band transmitter. A flywheel provides 1-axis stabilization during the descent. Total mass of the lander is about 100 kg. Philae will be carried on the side of the Rosetta orbiter until it reaches the comet.

The Philae surface science package, with a total mass of about 21 kg, includes an alpha-proton-X-ray spectrometer (APXS) to determine elemental composition; two gas chromatograph/mass spectrometers: the Cometary Sampling and Composition Experiment (COSAC) and Methods Of Determining and Understanding Light elements from Unequivocal Stable isotope compositions (MODULUS/Ptolemy) to study composition, isotopic abundances and to identify complex organic molecules in cometary material; Surface Electrical, Seismic, and Acoustic Monitoring Experiments (SESAME) to investigate surface material acoustically, measure dielectric properties of the environment, and monitor dust impacts; Multi-Purpose Sensors for Surface and Subsurface Science (MUPUS) to study physical properties of the comet; Comet Nucleus Sounding Experiment By Radiowave Transmission (CONSERT) to investigate electrical characteristics of the nucleus bulk material and internal structure; Rosetta Lander Magnetic field investigation and Plasma monitor (ROMAP) to investigate the comet's magnetic field and interaction with the solar wind; in-situ imaging systems known as Comet Nucleus Infrared and Visible Analyser (CIVA) and the Rosetta Lander Imaging System (ROLIS), and a drill and sample collector (SD2).

Mission Profile

Rosetta and Philae were launched at 07:17 UT on 02 March 2004 on an Ariane 5 G+ from Kourou, French Guiana and will rendezvous with Comet Churyumov-Gerasimenko in mid-2014. The spacecraft will enter a heliocentric drift phase to intercept the comet at a point close enough to allow communication with the Earth in 2014. More details on the journey to the comet can be found in the Rosetta mission description at:

http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=2004-006A

On Rosetta's arrival at the comet and insertion into orbit, a suitable landing site was chosen (named Agilkia) based on the images sent back to Earth.

Philae ejected from Rosetta on 12 November, 2014 at 08:35 UT at an altitude of 21.8 km, unfolded its three legs, and began a 7-hour long free fall towards the surface in the low gravity. Touchdown occurred at 15:34:06 UT with confirmation at Earth arriving at 16:03 UT. However, the upper hold-down thruster and harpoons did not fire as planned and the lander rebounded from the surface. The original touchdown velocity was approximately 1 meter/sec, Philae rebounded at about 38 cm/sec and traveled about 1 km before hitting the ground about 1 hour and 50 minutes later (17:25 UT). It rebounded again at 3 cm/sec, remaining aloft for another 7 minutes before touching down and coming to rest at 17:32 UT in a then unknown location and orientation. (It was later determined to be in the Abydos region.) Telemetry and initial images were received as planned, but solar power was limited due to shadowing of the solar arrays. The main battery allowed deployment of the instruments and communications until the last session ended at 00:36 UT on 15 November. Philae completed its main mission and went into hibernation.

It achieved contact with Rosetta on 13 June 2015 after 7 months and appeared to be in good condition, but the session was limited, and only eight intermittent contacts were made up to July 9. The increased sunlight, which powered Philae and allowed it to operate, also had the effect of increasing activity on the comet, forcing Rosetta back to a higher orbit where communications with Philae were no longer possible. (Good communications require an orbit within 200 km.) With decreasing activity Rosetta is lowering its orbit, dipping to 170 km on 12 November 2015, allowing possible contact. It appears that one of the two receivers and one of the two transmitters on Philae is no longer working, and the other transmitter is experiencing problems. As the comet moves away from the Sun, temperatures will get colder, at the end of January 2016 the internal temperature of Philae will probably get below the operational temperature of -51 degrees C.

Philae is named after the island in the river Nile on which an obelisk was found that had a bilingual inscription including the names of Cleopatra and Ptolemy in Egyptian hieroglyphs. This provided the French historian Jean-Francois Champollion with the final clues that enabled him to decipher the hieroglyphs of the Rosetta Stone and unlock secrets of the civilization of ancient Egypt. The target landing region was named Agilkia after the island in the Nile to which monuments on the island of Philae were moved so they would not be submerged due to the construction of the Aswan Dam.

Alternate Names

  • Rosetta Lander

Facts in Brief

Launch Date: 2004-03-02
Launch Vehicle: Ariane 5G
Launch Site: Kourou, French Guiana
Mass: 100.0 kg

Funding Agency

  • European Space Agency (International)

Discipline

  • Planetary Science

Additional Information

Questions or comments about this spacecraft can be directed to: Dr. David R. Williams.

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Helmut R. RosenbauerProject ScientistMax-Planck-Institut fur Aeronomierosenbauer@linmpi.mpg.de
Dr. Stephan UlamecProject ManagerDeutsche Forschungsenstalt fuer Luft-und Raumfahrtstephan.ulamec@dlr.de
Prof. Denis MouraProject ManagerCentre National d'Etudes Spatialesdenis.moura@cnes.fr
Dr. Jean-Pierre BibringProject ScientistInstitut d Astrophysique Spatialejean-pierre.bibring@ias.u-psud.fr

Selected References

Biele, J., The experiments onboard the Rosetta lander, Earth, Moon, Planet., 90, 445-458, 2002.

Ulamec, S., et al., Rosetta Lander - Philae: Implications of an alternative mission, Acta Astronaut., 58, No. 8, 435-441, Apr. 2006.

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