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Philae (spacecraft)

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Philae
Illustration of Philae approaching a comet
Mission typeComet lander
OperatorEuropean Space Agency
COSPAR IDPHILAE
Websitewww.esa.int/rosetta
Mission duration1–6 weeks (planned)
Spacecraft properties
Launch mass100 kg (220 lb)[1]
Payload mass21 kg (46 lb)[1]
Dimensions1 × 1 × 0.8 m (3.3 × 3.3 × 2.6 ft)[1]
Power32 watts at 3 AU[2]
Start of mission
Launch date2 March 2004, 07:17 (2004-03-02UTC07:17Z) UTC
RocketAriane 5G+ V-158
Launch siteKourou ELA-3
ContractorArianespace
67P/Churyumov–Gerasimenko lander
Landing date12 November 2014
15:35 UTC
Instruments
APX Alpha: Alpha Particle 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 (/ˈfaɪliː/) is a robotic European Space Agency lander that accompanied the Rosetta spacecraft[3] until its designated landing on Comet 67P/Churyumov–Gerasimenko, more than ten years after departing Earth.[4][5][6] On 12 November 2014, the lander achieved the first-ever controlled touchdown on a comet nucleus.[7] Its instruments are expected to obtain the first images from a comet's surface and make the first in situ analysis to determine its composition.[8]

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.

Mission

Video report by the German Aerospace Center about Philae's landing mission. (10 min, English, in 1080p HD)

Philae's mission is to land successfully on the surface of a comet, attach itself, 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 2009. 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".[9]

Scientific goals

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."[10]

Landing

Photograph of comet 67P taken by Philae approximately 10 km from the surface on 9 November 2014

On 12 November 2014, Philae remained attached to the Rosetta spacecraft after rendezvousing with comet 67P/Churyumov–Gerasimenko. On 15 September 2014, ESA announced Site J, named Agilkia in honour of Agilkia Island by an ESA public contest,[11] on the "head" of the comet as the lander's destination.[12]

Philae detached from Rosetta on 12 November 2014 at 08:35 UTC, landing seven hours later at 15:35.[13][14] A confirmed landing signal was received at 16:03 UTC.[15][1]

A final test before descent showed that the lander's thruster was not working correctly.[16][17] Philae's touchdown on the comet 67P/C-G was confirmed on 12 November 2014, 16:08 UTC. In an update from the LCC in ESA's live stream at 16:42 UTC, it was announced that analysis of telemetry indicated that the landing was softer than expected, that the harpoons had not fired upon landing, and that the thruster had not worked.[18][19][20]

Design

Rosetta and Philae

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.[21] 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).[22] The legs were designed to dampen the initial impact to avoid bouncing as the comet's escape velocity is only around 0.5 m/s (1.8 km/h; 1.1 mph),[23] and the impact energy would drive ice screws into the surface.[24] Philae would then fire two harpoons into the surface at 70 m/s (250 km/h; 160 mph) to anchor itself.[25][26] A thruster on top of Philae would fire to lessen the bounce upon impact and to reduce the recoil from harpoon firing. [16]

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]

Philae landing site Agilkia (Site J)

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 mass of comet 67P/C-G and the resulting increased impact velocity required that the landing gear of the redesigned lander be strengthened, in order for the spacecraft and its delicate scientific instruments to survive the landing.

Spacecraft component Mass[10]: 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

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".[9]

Instruments

Philae's instruments

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.[10]

APXS
The Alpha Particle X-ray Spectrometer detects alpha particles and X-rays, which provide information on the elemental composition of the comet's surface.[27] The instrument is an improved version of the APXS of the Mars Pathfinder.
COSAC
The COmetary SAmpling and Composition instrument is a combined gas chromatograph and time-of-flight mass spectrometer perform analysis of soil samples and determine the content of volatile components.[28][29]
Ptolemy
An instrument measuring stable isotope ratios of key volatiles on the comet's nucleus.[30][31]
ÇIVA
The 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.[32] A spectrometer studies the composition, texture and albedo (reflectivity) of samples collected from the surface.[33]
ROLIS
The 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.[34] The CCD detector consists of 1024×1024 pixels.[35]
CONSERT
The COmet Nucleus Sounding Experiment by Radiowave Transmission experiment will use electromagnetic wave propagation to determine the comet's internal structure. A radar on Rosetta will transmit a signal through the nucleus to be received by a detector on Philae.[36][37]
MUPUS
The MUlti-PUrpose Sensors for Surface and Sub-Surface Science instrument will measure the density, thermal and mechanical properties of the comet's surface.[38]
ROMAP
The Rosetta Lander Magnetometer and Plasma Monitor is a magnetometer and plasma sensor to study the nucleus' magnetic field and its interactions with the solar wind.[39]
SESAME
The 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.[40]
SD2
The 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.[41] The system contains four types of subsystems: drill, carousel, ovens, and volume checker.[42] 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.[43]

International contributions

Austria
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.
Finland
The Finnish Meteorological Institute provided the Memory of the Command, Data and Management System (CDMS) and the Permittivity Probe (PP).
France
The French Space Agency together with some scientific laboratories (IAS, SA, LPG, LISA) provided the system's overall engineering, radiocommunications, battery assembly, CONSERT, ÇIVA and the ground segment (overall engineering and development/operation of the Scientific Operation & Navigation Centre).
Germany
The German Space Agency (DLR) has provided the structure, thermal subsystem, flywheel, the Active Descent System (procured by DLR but made in Switzerland),[44] 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 Münster built MUPUS (it was designed and built in Space Research Centre of Polish Academy of Sciences [45]) 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.
Hungary
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.
Italy
The Italian Space Agency (ASI) has provided the SD2 instrument and the Photo Voltaic Assembly. The industrial contractors are respectively Tecnospazio SpA and Galileo Avionica SpA.
Ireland
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.
Netherlands
Moog Bradford (Heerle, The Netherlands) provided the Active Descent System (ADS) that is intended to provide the required impulse to ensure that Philae will descend towards the nucleus of comet 67P/Churyumov-Gerasimenko in 2014. To accomplish the ADS, a strategic industrial team was formed with Bleuler-Baumer Mechanik in Switzerland.[44]
Poland
The Space Research Centre of the Polish Academy of Sciences built MUPUS.[45]
Switzerland
The Swiss Center for Electronics and Microtechnology developed ÇIVA.[46]
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.[47]

Trivia

On 12 November 2014, to commemorate the first controlled touchdown of Philae on a comet nucleus, the search engine Google featured a Google Doodle on its home page.[48][49]

Gallery

  • Depiction of Philae's touchdown on the comet
    Depiction of Philae's touchdown on the comet
  • Philae's foot screws
    Philae's foot screws

See also

References

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  2. ^ "Philae lander fact sheet" (PDF). DLR. Retrieved 28 January 2014.
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  4. ^ Ulamec, S.; Espinasse, S.; Feuerbacher, B.; Hilchenbach, M.; Moura, D.; et al. (April 2006). "Rosetta Lander—Philae: Implications of an alternative mission". Acta Astronautica. 58 (8): 435–441. Bibcode:2006AcAau..58..435U. doi:10.1016/j.actaastro.2005.12.009.
  5. ^ a b Biele, Jens (2002). "The Experiments Onboard the ROSETTA Lander". Earth, Moon, and Planets. 90 (1–4): 445–458. Bibcode:2002EM&P...90..445B. doi:10.1023/A:1021523227314.
  6. ^ Agle, D. C.; Cook, Jia-Rui; Brown, Dwayne; Bauer, Markus (17 January 2014). "Rosetta: To Chase a Comet". NASA. Retrieved 18 January 2014.
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  13. ^ "Rosetta to Deploy Lander on 12 November". European Space Agency. 26 September 2014. Retrieved 4 October 2014.
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  18. ^ Cite error: The named reference CNNvideo was invoked but never defined (see the help page).
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  24. ^ Böhnhardt, Hermann (10 November 2014). "About the Upcoming Philae Separation, Descent and Landing". Max Planck Institute for Solar System Research. Retrieved 11 November 2014.
  25. ^ Biele, J.; Ulamec, S.; Richter, L.; Kührt, E.; Knollenberg, J.; Möhlmann, D. (2009). "The Strength of Cometary Surface Material: Relevance of Deep Impact Results for Philae Landing on a Comet". In Käufl, Hans Ulrich; Sterken, Christiaan (eds.). Deep Impact as a World Observatory Event: Synergies in Space, Time, and Wavelength. ESO Astrophysics Symposia. Springer. p. 297. Bibcode:2009diwo.conf..285B. doi:10.1007/978-3-540-76959-0_38. ISBN 978-3-540-76958-3. {{cite book}}: External link in |chapterurl= (help); Unknown parameter |chapterurl= ignored (|chapter-url= suggested) (help)
  26. ^ Biele, Jens; Ulamec, Stephan (2013). Preparing for Landing on a Comet - The Rosetta Lander Philae (PDF). 44th Lunar and Planetary Science Conference. 18–22 March 2013. The Woodlands, Texas. Bibcode:2013LPI....44.1392B. LPI Contribution No. 1719.
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  30. ^ Wright, I. P.; Barber, S. J.; Morgan, G. H.; Morse, A. D.; Sheridan, S.; et al. (February 2007). "Ptolemy: An Instrument to Measure Stable Isotopic Ratios of Key Volatiles on a Cometary Nucleus". Space Science Reviews. 128 (1–4): 363–381. Bibcode:2007SSRv..128..363W. doi:10.1007/s11214-006-9001-5.
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  40. ^ Seidensticker, K. J.; Möhlmann, D.; Apathy, I.; Schmidt, W.; Thiel, K.; et al. (February 2007). "Sesame – An Experiment of the Rosetta Lander Philae: Objectives and General Design". Space Science Reviews. 128 (1–4): 301–337. Bibcode:2007SSRv..128..301S. doi:10.1007/s11214-006-9118-6.
  41. ^ "SD2". European Space Agency. Retrieved 26 August 2014.
  42. ^ "Philae SD2". Politecnico di Milano. Retrieved 11 August 2014.
  43. ^ "Ovens". Politecnico di Milano. Retrieved 11 August 2014.
  44. ^ a b "Active Descent System" (PDF). Moog Inc. Retrieved 11 November 2014.
  45. ^ a b "The MUPUS Instrument for Rosetta mission to comet Churyumov-Gerasimenko". Laboratorium Mechatroniki i Robotyki Satelitarnej. 2014. Retrieved 6 August 2014.
  46. ^ "CIVA Project". 2014. Retrieved 7 November 2014.
  47. ^ "Philae Lander Fact Sheets" (PDF). DLR. 2004. Retrieved 11 November 2014.
  48. ^ Solon, Olivia (12 November 2014). "Philae: Google Doodle marks Rosetta's historic comet landing". Mirror. Retrieved 12 November 2014.
  49. ^ "Google Doodles". Google. 12 November 2014. Retrieved 12 November 2014. {{cite news}}: Cite has empty unknown parameter: |1= (help)

External links

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Further reading
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