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définition - Herschel_Space_Observatory

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Wikipedia

Herschel Space Observatory

                   
Herschel Space Observatory
Herschel Space Observatory.jpg
General information
NSSDC ID 2009-026A
Organization European Space Agency (ESA)
NASA
Major contractors Thales Alenia Space
Launch date 2009:05:14, 13:12:02 UTC
Launched from Guiana Space Centre
French Guiana
Launch vehicle Ariane 5 ECA
Mission length planned: 3 years
elapsed: 3 years, 1 month and 28 days
Mass 3,300 kg (7,300 lb)
Type of orbit Lissajous orbit
Orbit height 1,500,000 km (930,000 mi)
Orbit period 1 year
Orbit velocity 7,500 m/s (27,000 km/h)
Location Lagrangian point L2
Telescope style Ritchey-Chrétien
Wavelength 60-670 µm (far-infrared)
Diameter 3,500 mm (140 in), f/0.5 (Primary Mirror)
Collecting area 9.6 m2 (103 sq ft)
Focal length 28.5 m (94 ft), f/8.7
Instruments
HIFI Heterodyne Instrument for the Far Infrared
PACS Photodetector Array Camera and Spectrometer
SPIRE Spectral and Photometric Imaging Receiver
Website herschel.esac.esa.int

The Herschel Space Observatory is a European Space Agency space observatory sensitive to the far infrared and submillimetre wavebands. It is the largest infrared space telescope ever launched, carrying a single mirror of 3.5 metres (11.5 ft) in diameter.[1][2][3]

The observatory was carried into orbit in May 2009, reaching the second Lagrangian point (L2) of the Earth-Sun system, 1,500,000 kilometres (930,000 mi) from the Earth, about two months later. Herschel is named after Sir William Herschel, the discoverer of the infrared spectrum and planet Uranus, and his sister and collaborator Caroline.[4]

The Herschel Observatory is capable of seeing the coldest and dustiest objects in space; for example, cool cocoons where stars form and dusty galaxies just starting to bulk up with new stars.[5] The observatory will sift through star-forming clouds—the "slow cookers" of star ingredients—to trace the path by which potentially life-forming molecules, such as water, form. The United States through NASA is participating in the ESA-built and -operated observatory.[6] It is the fourth 'cornerstone' mission in the ESA science program, along with Rosetta, Planck, and the Gaia mission.

Contents

  Development

In 1982 the Far Infrared and Sub-millimetre Telescope (FIRST) was proposed to ESA. The ESA long-term policy-plan "Horizon 2000", produced in 1984, called for a "High Throughput Heterodyne Spectroscopy mission" as one of its cornerstone missions. In 1986, FIRST was adopted as this cornerstone mission.[7] It was selected for implementation in 1993, following an industrial study in 1992-1993. The mission concept was redesigned from Earth-orbit to the Lagrangian point L2, in light of experience gained from the Infrared Space Observatory. In 2000, FIRST was renamed Herschel. After being put out to tender in 2000, industrial activities began in 2001.[8] Herschel was launched in 2009.

  Science

Herschel will specialise in collecting light from objects in our Solar System as well as the Milky Way and even extragalactic objects billions of light-years away, such as newborn galaxies, and is charged with four primary areas of investigation:[9]

  Instrumentation

The mission involves the first space observatory to cover the full far infrared and submillimetre waveband.[9] At 3.5 meters wide, its telescope incorporates the largest mirror (made not from glass but from sintered silicon carbide) ever deployed in space.[10] The light is focused onto three instruments with detectors kept at temperatures below 2 K (−271 °C). The instruments are cooled with liquid helium, boiling away in a near vacuum at a temperature of approximately 1.4 K (−272 °C). The 2,000-litre supply of helium on board the spacecraft will limit its operational lifetime; nonetheless, it is expected to be operational for at least 3 years.[11]

Herschel carries three detectors:[12]

PACS (Photodetecting Array Camera and Spectrometer)
An imaging camera and low-resolution spectrometer covering wavelengths from 55 to 210 micrometres. The spectrometer has a spectral resolution between R=1000 and R=5000 and is able to detect signals as weak as −63 dB. It operates as an integral field spectrograph, combining spatial and spectral resolution. The imaging camera can image simultaneously in two bands (either 60–85/85–130 micrometres and 130–210 micrometres) with a detection limit of a few millijanskys.[13][14]
  Herschel in a clean room
SPIRE (Spectral and Photometric Imaging Receiver)
An imaging camera and low-resolution spectrometer covering 194 to 672 micrometre wavelength. The spectrometer has a resolution between R=40 and R=1000 at a wavelength of 250 micrometres and is able to image point sources with brightnesses around 100 millijanskys (mJy) and extended sources with brightnesses of around 500 mJy.[15] The imaging camera has three bands, centered at 250, 350 and 500 micrometres, each with 139, 88 and 43 pixels respectively. It should be able to detect point sources with brightness above 2 mJy and between 4 and 9 mJy for extended sources. A prototype of the SPIRE imaging camera flew on the BLAST high-altitude balloon. NASA's Jet Propulsion Laboratory in Pasadena, Calif., developed and built the "spider web" bolometers for this instrument, which is 40 times more sensitive than previous versions. The Herschel-SPIRE instrument was built by an international consortium comprising more than 18 institutes from eight countries, of which Cardiff University was the lead institute.[16]
HIFI (Heterodyne Instrument for the Far Infrared)
A heterodyne detector which is able to electronically separate radiation of different wavelengths, giving a spectral resolution as high as R=107.[17] The spectrometer can be operated within two wavelength bands, from 157 to 212 micrometres and from 240 to 625 micrometres. SRON Netherlands Institute for Space Research has led the entire process of designing, constructing and testing HIFI. The HIFI Instrument Control Center, also under the leadership of SRON, is responsible for obtaining and analysing the data.

NASA developed and built the mixers, local oscillator chains and power amplifiers for this instrument.[18]

  Service module

A common service module (SVM) was designed and built by Thales Alenia Space in its Turin plant, for the Herschel and Planck missions combined into one single program.[19]

Structurally, the Herschel and Planck SVM's are very similar. Both SVM's are of octagonal shape and for both, each panel is dedicated to accommodate a designated set of warm units, while taking into account the dissipation requirements of the different warm units, of the instruments as well as the spacecraft.

Furthermore, on both spacecraft a common design for the avionics, the attitude control and measurement system (ACMS) and the command and data management system (CDMS), and power subsystem and the tracking, telemetry and command subsystem (TT&C) has been achieved.

All spacecraft units on the SVM are redundant.

  Power subsystem

On each spacecraft, the power subsystem consists of the solar array, employing triple-junction solar cells, a battery and the power control unit (PCU). It is designed to interface with the 30 sections of each solar array, provide a regulated 28 V bus, distribute this power via protected outputs and to handle the battery charging and discharging.

For Herschel, the solar array is fixed on the bottom part of the baffle designed to protect the cryostat from the sun. The three-axis attitude control system maintains this baffle in direction of the sun. The top part of this baffle is covered with optical solar reflector (OSR) mirrors reflecting 98% of the sun energy, avoiding heating of the cryostat.

  Attitude and orbit control

This function is performed by the attitude control computer (ACC) which is the platform for the ACMS. It is designed to fulfil the pointing and slewing requirements of the Herschel and Planck payload.

The Herschel spacecraft is three-axis stabilized, the absolute pointing error needs to be less than 3.7 arc sec.

The main sensor of the line of sight in both spacecraft is the star tracker.

  Launch and orbit

The spacecraft, built in the Cannes Mandelieu Space Center, under Thales Alenia Space Contractorship, was successfully launched from the Guiana Space Centre in French Guiana at 13:12:02 UTC on 14 May 2009, aboard an Ariane 5 rocket, along with the Planck spacecraft, and placed on a very elliptical orbit (perigee: 270.0 km (intended 270.0±4.5), apogee: 1,197,080 km (intended 1,193,622±151,800), inclination 5.99 deg (intended 6.00±0.06)[20]), on its way towards the second Lagrangian point.[21][22][23]

On June 14, 2009, ESA successfully sent the command for the cryocover to open which will allow the PACS system to see the sky and transmit images in a few weeks. The lid had to remain closed until the telescope was well into space to prevent contamination. Herschel was reported to have completed 90% of the distance to its orbit 1.5 million km away from Earth.[24]

Five days later the first set of test photos, depicting M51 Group, was published by ESA.[25]

In mid-July 2009, approximately sixty days after launch, it entered a Lissajous orbit of 800,000 km average radius around the second Lagrangian point (L2) of the Earth-Sun system, 1.5 million kilometres from the Earth.[23][26]

  Operational mission

On 21 July 2009, Herschel commissioning was declared successful, allowing the start of the operational phase. A formal handover of the overall responsibility of Herschel was declared from the programme manager Thomas Passvogel to the mission manager Johannes Riedinger.[23]

  Discoveries

  André Brahic, astronomer, during a conference in the Cannes Mandelieu Space Center

Herschel was instrumental in the discovery of an unknown and unexpected step in the star forming process. The initial confirmation and later verification via help from ground based telescopes of a vast hole of empty space, previously believed to be a dark nebula, in the area of NGC 1999 shed new light in the way newly forming star regions discard the material which surround them.[27]

In July 2010 a special issue of Astronomy and Astrophysics was published with 152 papers on initial results from the observatory.[28]

A second special issue of Astronomy and Astrophysics was published in October 2010 concerning the sole HIFI instrument, due its technical failure which took it down over 6 months between August 2009 and February 2010.[29]

It was reported on August 1, 2011, that molecular oxygen had been definitively confirmed in space with the Herschel Space Telescope, the second time scientists have found the molecule in space. It had been previously reported by the Odin team.[30][31]

An October 2011 report published in Nature states that Herschel's measurements of deuterium levels in the comet Hartley 2 suggests that much of Earth's water could have initially come from cometary impacts.[32]

On October 20, 2011, it was reported that oceans-worth of cold water vapor had been discovered in the accretion disc of a young star. Unlike warm water vapor, previously detected near forming stars, cold water vapor would be capable of forming comets which then could bring water to inner planets, as is theorized for the origin of water on Earth.[33]

  See also

  References

  1. ^ "ESA launches Herschel and Planck space telescopes". Euronews. http://www.euronews.net/2009/05/14/esa-launches-herschel-and-planck-space-telescopes. Retrieved 3 December 2010. 
  2. ^ Amos, Jonathan (14 June 2009). "ESA launches Herschel and Planck space telescopes". BBC. http://news.bbc.co.uk/2/hi/science/nature/8099105.stm. Retrieved 3 December 2010. 
  3. ^ "ESA launches Herschel and Planck space telescopes". Aerospaceguide. http://www.aerospaceguide.net/telescope/herschel.html. Retrieved 3 December 2010. 
  4. ^ "Revealing the invisible: Caroline and William Herschel". ESA. 18 June 2000. http://www.esa.int/SPECIALS/Herschel/SEM8600P4HD_0.html. Retrieved 22 July 2010. 
  5. ^ ESA Science & Technology: Herschel. Retrieved on 28 July 2010
  6. ^ "NSSDC Spacecraft Details: Herschel Space Observatory". NASA. http://nssdc.gsfc.nasa.gov/nmc/masterCatalog.do?sc=2009-026A. Retrieved 3 July 2010. 
  7. ^ The First Mission: Baseline, Science Objectives and Operations, Authors: Pilbratt, G. Journal: The Far Infrared and Submillimetre Universe. 1997., p.7
  8. ^ Herschel Space Observatory? An ESA facility for far-infrared and submillimetre astronomy, G.L. Pilbratt, J.R. Riedinger, T. Passvoge, G. Crone, D. Doyle, U. Gageur, A.M. Heras, C. Jewell, L. Metcalfe, S. Ott, and M. Schmidt
  9. ^ a b "Herschel". European Space Agency Science & Technology. http://sci.esa.int/science-e/www/area/index.cfm?fareaid=16. Retrieved 2007-09-29. 
  10. ^ "Herschel Space Observatory". Imperial College. http://astro.imperial.ac.uk/Research/Infrared/Herschel/. Retrieved 2007-09-29. [dead link]
  11. ^ Jonathan Amos (9 February 2009). "'Silver Sensation' Seeks Cold Cosmos". BBC News. http://news.bbc.co.uk/2/hi/science/nature/7864087.stm. Retrieved 2009-03-06. 
  12. ^ "Herschel: Science payload". European Space Agency. 20 November 2008. http://www.esa.int/esaSC/120390_index_0_m.html. Retrieved 2009-03-07. 
  13. ^ "PACS – Photodetector Array Camera and Spectrometer". http://herschel.esac.esa.int/Docs/Flyers/PACS_flyer_4July2007.pdf. Retrieved 2007-09-29. 
  14. ^ "The Photodetector Array Camera and Spectrometer (PACS) for the Herschel Space Observatory". http://herschel.esac.esa.int/Publ/2008/SPIE2008_PACS_paper.pdf. Retrieved 2009-08-19. 
  15. ^ "SPIRE – Spectral and Photometric Imaging Receiver". European Space Agency. http://herschel.esac.esa.int/Docs/Flyers/SPIRE_flyer_4July2007.pdf. Retrieved 2007-09-29. 
  16. ^ http://www.esa.int/esaMI/Herschel/SEMGT00YUFF_0.html Herschel Instruments
  17. ^ "HIFI – Heterodyne Instrument for the Far Infrared". European Space Agency. http://herschel.esac.esa.int/Docs/Flyers/HIFI_flyer_4July2007.pdf. Retrieved 2007-09-29. 
  18. ^ "Herschel: Exploring the Birth of Stars and Galaxies". NASA. http://www.nasa.gov/mission_pages/herschel/overview.html. 
  19. ^ Planck Science Team (2005) (.PDF). Planck: The Scientific Programme (Blue Book). ESA-SCI (2005)-1. Version 2. European Space Agency. http://www.rssd.esa.int/SA/PLANCK/docs/Bluebook-ESA-SCI%282005%291_V2.pdf. Retrieved 2009-03-06. 
  20. ^ Herschel Science Centre Operations (B)Log. European Space Agency. 14 May 2009. Retrieved on 2009-05-18
  21. ^ Leo Cendrowicz (14 May 2009). "Two Telescopes to Measure the Big Bang". Time. http://www.time.com/time/health/article/0,8599,1898174,00.html. Retrieved 2009-05-16. 
  22. ^ (.SWF) Launch of Herschel and Planck satellites (video). Arianespace. 14 May 2009. http://www.videocorner.tv/videocorner2/live_flv/index.php?langue=en. Retrieved 2009-05-16. 
  23. ^ a b c Herschel Latest News, on line herschel.esac.esa.int
  24. ^ Amos, Jonathan (June 14, 2009). "Herschel telescope 'opens eyes'". BBC News. http://news.bbc.co.uk/2/hi/science/nature/8099105.stm. Retrieved June 14, 2009. 
  25. ^ "Herschel's 'sneak preview': a glimpse of things to come". ESA. 2009-06-19. http://herschel.esac.esa.int/SneakPreview.shtml. Retrieved 2009-06-19. 
  26. ^ "Herschel Factsheet". European Space Agency. 17 April 2009. http://www.esa.int/esaSC/SEMA539YFDD_index_0.html. Retrieved 2009-05-12. 
  27. ^ Staff (May 11, 2010). "Surprising Hole in Space Discovered by Herschel Telescope". Space.com. http://www.space.com/8378-surprising-hole-space-discovered-herschel-telescope.html. Retrieved May 1, 2012. 
  28. ^ "A&A special feature: Herschel: the first science highlights" (Press release). Astronomy & Astrophysics. July 16, 2010. ID# aa201003. http://www.aanda.org/index.php?option=com_content&view=article&id=588&Itemid=270&lang=en. Retrieved May 1, 2012. 
  29. ^ "Herschel/HIFI: first science highlights". Astronomy & Astrophysics. October 2010. http://www.aanda.org/index.php?option=com_toc&url=/articles/aa/abs/2010/13/contents/contents.html. Retrieved May 1, 2012. 
  30. ^ Goldsmith, Paul F; et al. (August 2011). "Herschel measurement of molecular oxygen in Orion". Astrophysical Journal 737 (2). DOI:10.1088/0004-637X/737/2/96. 
  31. ^ Larsson, B; et al. (May 2007). "Molecular oxygen in the ρ Ophiuchi cloud". Astronomy & Astrophysics 466 (3). DOI:10.1051/0004-6361:20065500. 
  32. ^ Cowen, Ron (October 5, 2011). "Comets take pole position as water bearers". Nature. DOI:10.1038/news.2011.579. 
  33. ^ "Herschel Finds Oceans of Water in Disk of Nearby Star" (Press release). Herschel Space Observatory. October 20, 2011. ID# nhsc2011-018. http://www.herschel.caltech.edu/index.php?SiteSection=News&NewsItem=nhsc2011-018. Retrieved May 1, 2012. 

  Further reading

  External links

   
               

 

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