Herschel Space Observatory#Instrumentation

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.{{cite conference |url=http://herschel.esac.esa.int/Publ/1997/sp401-first.pdf |title=The FIRST Mission: Baseline, Science Objectives and Operations |conference=ESA Symposium 'The Far InfraRed and Submillimetre Universe' |volume=401 |publisher=European Space Agency |first=Göran |last=Pilbratt |editor-first=A. |editor-last=Wilson |pages=7–12 |date=August 1997 |id=ESA SP-401 |bibcode=1997ESASP.401....7P |archive-url=https://web.archive.org/web/20230531024920/http://herschel.esac.esa.int/Publ/1997/sp401-first.pdf |archive-date=31 May 2023 |url-status=live }} 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 [(2.5–240 μm) 1995–1998]. In 2000, FIRST was renamed Herschel. After being put out to tender in 2000, industrial activities began in 2001.{{cite journal |title=Herschel Space Observatory: An ESA facility for far-infrared and submillimetre astronomy |journal=Astronomy and Astrophysics |first1=G. L. |last1=Pilbratt |first2=J. R. |last2=Riedinger |first3=T. |last3=Passvogel |first4=G. |last4=Crone |first5=D. |last5=Doyle |first6=U. |last6=Gageur |first7=A. M. |last7=Heras |first8=C. |last8=Jewell |first9=L. |last9=Metcalfe |first10=S. |last10=Ott |first11=M. |last11=Schmidt |display-authors=1 |volume=518 |at=L1 |date=July 2010 |doi=10.1051/0004-6361/201014759 |bibcode=2010A&A...518L...1P |arxiv=1005.5331|s2cid=118533433 }} Herschel was launched in 2009.

The Herschel mission cost {{€|1,100 million}}.{{cite news |title=Largest Infrared Telescope In Space Running Out of Time |url=https://www.space.com/20120-herschel-space-telescope-mission-ending.html |access-date=2022-04-18 |work=Space.com |date=2013-03-08 |archive-url=https://web.archive.org/web/20211108122904/https://www.space.com/20120-herschel-space-telescope-mission-ending.html |archive-date=2021-11-08 |url-status=live}} This figure includes spacecraft and payload, launch and mission expenses, and science operations.{{cite web |url=http://esamultimedia.esa.int/docs/herschel/Herschel-Factsheet.pdf |title=Herschel: Fact Sheet |work=ESA.int |publisher=ESA Media Relations Office |date=28 April 2010 |archive-url=https://web.archive.org/web/20121018233814/http://esamultimedia.esa.int/docs/herschel/Herschel-Factsheet.pdf |archive-date=18 October 2012 |url-status=live }}

Herschel specialised in collecting light from objects in the Solar System as well as the Milky Way and even extragalactic objects billions of light-years away, such as newborn galaxies, and was charged with four primary areas of investigation:

• Galaxy formation in the early universe and the evolution of galaxies;
• Star formation and its interaction with the interstellar medium;
• Chemical composition of atmospheres and surfaces of Solar System bodies, including planets, comets and moons;
• Molecular chemistry across the universe.

During the mission, Herschel "made over 35,000 scientific observations" and "amass[ed] more than 25,000 hours' worth of science data from about 600 different observing programs".{{cite news |url=http://www.universetoday.com/101828/herschel-space-telescope-closes-its-eyes-on-the-universe/ |work=Universe Today |access-date=29 April 2013 |date=29 April 2013 |first=Nancy |last=Atkinson |title=Herschel Space Telescope Closes Its Eyes on the Universe}}

The mission involved the first space observatory to cover the full far infrared and submillimetre waveband.{{cite web |url=http://sci.esa.int/science-e/www/area/index.cfm?fareaid=16 |title=Herschel |publisher=European Space Agency Science & Technology |access-date=29 September 2007}} At {{convert|3.5|m|ft|disp=x| wide (|)}}, Herschel carried the largest optical telescope ever deployed in space.{{cite book |chapter-url=http://herschel.esac.esa.int/Publ/2002/telescope_spie02.pdf |title=IR Space Telescopes and Instruments |publisher=SPIE |editor1-last=Mather |editor1-first=John C |first1=Emmanuel |last1=Sein |first2=Yves |last2=Toulemont |first3=Frederic |last3=Safa |first4=Michel |last4=Duran |first5=Pierre |last5=Deny |first6=Daniel |last6=de Chambure |first7=Thomas |last7=Passvogel |first8=Goeran L. |last8=Pilbratt |chapter=A Φ 3.5m diameter Sic telescope for Herschel mission |volume=4850 |pages=606–618 |date=March 2003 |doi=10.1117/12.461804 |bibcode=2003SPIE.4850..606S|s2cid=120086590 }} It was made not from glass but from sintered silicon carbide. The mirror's blank was manufactured by Boostec in Tarbes, France; ground and polished by Opteon Ltd. in Tuorla Observatory, Finland; and coated by vacuum deposition at the Calar Alto Observatory in Spain.{{cite web |url=http://www.esa.int/Our_Activities/Space_Science/Herschel/The_largest_telescope_mirror_ever_put_into_space |title=The largest telescope mirror ever put into space |publisher=ESA |access-date=19 July 2013}}

The light reflected by the mirror was focused onto three instruments, whose detectors were kept at temperatures below {{convert|2|K|C|0}}.{{cite news |title=Herschel to finish observing soon |url=http://sci.esa.int/herschel/51468-herschel-to-finish-observing-soon/ |work=ESA |date=5 March 2013 |access-date=18 July 2014}} The instruments were cooled with over {{convert|2300|L}} of liquid helium, boiling away in a near vacuum at a temperature of approximately {{convert|1.4|K|C|0}}. The supply of helium on board the spacecraft was a fundamental limit to the operational lifetime of the space observatory; it was originally expected to be operational for at least three years.{{cite news |author=Jonathan Amos |title='Silver Sensation' Seeks Cold Cosmos |url=http://news.bbc.co.uk/2/hi/science/nature/7864087.stm |work=BBC News |date=9 February 2009 |access-date=6 March 2009}}

Herschel carried three detectors:{{cite web |url=http://www.esa.int/esaSC/120390_index_0_m.html |title=Herschel: Science payload |publisher=European Space Agency |date=20 November 2008 |access-date=7 March 2009}}

; {{anchor|PACS}} PACS (Photodetecting Array Camera and Spectrometer): An imaging camera and low-resolution spectrometer covering wavelengths from 55 to 210 micrometres, which was designed and built by the Max Planck Institute for Extraterrestrial Physics. The spectrometer had a spectral resolution between R=1000 and R=5000 and was able to detect signals as weak as −63 dB. It operated as an integral field spectrograph, combining spatial and spectral resolution. The imaging camera was able to image simultaneously in two bands (either 60–85/85–130 micrometres and 130–210 micrometres) with a detection limit of a few millijanskys.{{cite web |url=http://herschel.esac.esa.int/Docs/Flyers/PACS_flyer_4July2007.pdf |title=PACS – Photodetector Array Camera and Spectrometer |access-date=29 September 2007}}{{cite web |url=http://herschel.esac.esa.int/Publ/2008/SPIE2008_PACS_paper.pdf |title=The Photodetector Array Camera and Spectrometer (PACS) for the Herschel Space Observatory |access-date=19 August 2009}}

File:Herschel SPIRE model at NAM 2012 1.jpg

File:Herschel Space Observatory at ESTEC.JPG

; SPIRE (Spectral and Photometric Imaging Receiver): An imaging camera and low-resolution spectrometer covering 194 to 672 micrometre wavelength. The spectrometer had a resolution between R=40 and R=1000 at a wavelength of 250 micrometres and was able to image point sources with brightnesses around 100 millijanskys (mJy) and extended sources with brightnesses of around 500 mJy.{{cite web |url=http://herschel.esac.esa.int/Docs/Flyers/SPIRE_flyer_4July2007.pdf |title=SPIRE – Spectral and Photometric Imaging Receiver |publisher=European Space Agency |access-date=29 September 2007}} The imaging camera had three bands, centred at 250, 350 and 500 micrometres, each with 139, 88 and 43 pixels respectively. It was 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.{{cite web |url=http://www.esa.int/esaMI/Herschel/SEMGT00YUFF_0.html |title=Herschel Instruments |publisher=Esa.int |access-date=2 May 2013}}

; HIFI (Heterodyne Instrument for the Far Infrared): A heterodyne detector able to electronically separate radiation of different wavelengths, giving a spectral resolution as high as R=10⁷.{{cite web |url=http://herschel.esac.esa.int/Docs/Flyers/HIFI_flyer_4July2007.pdf |title=HIFI – Heterodyne Instrument for the Far Infrared |publisher=European Space Agency |access-date=29 September 2007}} The spectrometer was operated within two wavelength bands, from 157 to 212 micrometres and from 240 to 625 micrometres. SRON Netherlands Institute for Space Research led the entire process of designing, constructing and testing HIFI. The HIFI Instrument Control Center, also under the leadership of SRON, was responsible for obtaining and analysing the data.

NASA developed and built the mixers, local oscillator chains and power amplifiers for this instrument.{{cite web |url=http://www.nasa.gov/mission_pages/herschel/overview.html |title=Herschel: Exploring the Birth of Stars and Galaxies |publisher=NASA |access-date=24 September 2009 |archive-date=28 October 2009 |archive-url=https://web.archive.org/web/20091028061423/http://www.nasa.gov/mission_pages/herschel/overview.html |url-status=dead }} The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at the California Institute of Technology, also in Pasadena, has contributed science planning and data analysis software.{{cite web |url=http://www.herschel.caltech.edu/page/nasa_contributions |title=NASA Contributions |publisher=NASA/IPAC}}

A common service module (SVM) was designed and built by Thales Alenia Space in its Turin plant for the Herschel and Planck missions, as they were combined into one single program.{{cite report |author=Planck Science Team |title=Planck: The Scientific Programme (Blue Book) |version=ESA-SCI (2005)-1. Version 2 |publisher=European Space Agency |url=http://www.rssd.esa.int/SA/PLANCK/docs/Bluebook-ESA-SCI%282005%291_V2.pdf |date=2005 |access-date=6 March 2009 |archive-url=https://web.archive.org/web/20090319070702/http://www.rssd.esa.int/SA/PLANCK/docs/Bluebook-ESA-SCI(2005)1_V2.pdf |archive-date=19 March 2009 |url-status=dead }}

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

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

All spacecraft units on the SVM are redundant.

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's energy, avoiding heating of the cryostat.

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 seconds.

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

File:Animation of Herschel Space Observatory trajectory.gif }}]]

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 on its way towards the second Lagrangian point.{{cite magazine |author=Leo Cendrowicz |url=http://www.time.com/time/health/article/0,8599,1898174,00.html |archive-url=https://web.archive.org/web/20090515212345/http://www.time.com/time/health/article/0,8599,1898174,00.html |url-status=dead |archive-date=15 May 2009 |magazine=Time |title=Two Telescopes to Measure the Big Bang |date=14 May 2009 |access-date=16 May 2009}}{{cite video |title=Launch of Herschel and Planck satellites |url=http://www.videocorner.tv/videocorner2/live_flv/index.php?langue=en |format=.SWF |medium=video |publisher=Arianespace |date=14 May 2009 |access-date=16 May 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090517082408/http://www.videocorner.tv/videocorner2/live_flv/index.php?langue=en |archive-date=17 May 2009 }}Herschel Latest News, [http://herschel.esac.esa.int/latest_news.shtml on line herschel.esac.esa.int] The orbit's perigee was 270.0 km (intended {{val|270.0|4.5}}), apogee 1,197,080 km (intended {{val|1,193,622|151,800}}), inclination 5.99 deg (intended {{val|6.00|0.06}}).[http://herschel.esac.esa.int/operations_log.shtml Herschel Science Centre Operations (B)Log]. European Space Agency. 14 May 2009. Retrieved on 18 May 2009

On 14 June 2009, ESA successfully sent the command for the cryocover to open which allowed 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.{{cite news |url=http://news.bbc.co.uk/2/hi/science/nature/8099105.stm |title=Herschel telescope 'opens eyes' |work=BBC News |first=Jonathan |last=Amos |date=14 June 2009 |access-date=14 June 2009}}

Five days later the first set of test photos, depicting M51 Group, was published by ESA.{{cite news |url=http://herschel.esac.esa.int/SneakPreview.shtml |title=Herschel's 'sneak preview': a glimpse of things to come |publisher=ESA |date=19 June 2009 |access-date=19 June 2009}}

In mid-July 2009, approximately sixty days after launch, it entered a halo 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.{{cite web |url=http://www.esa.int/esaSC/SEMA539YFDD_index_0.html |title=Herschel Factsheet |publisher=European Space Agency |access-date=12 May 2009 |date=17 April 2009}}

File:Embryonic Stars in the Rosette Nebula.jpg

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.

File:André Brahic Cannes.jpg, 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.{{cite news |url=http://www.space.com/8378-surprising-hole-space-discovered-herschel-telescope.html |title=Surprising Hole in Space Discovered by Herschel Telescope |work=Space.com |date=11 May 2010 |access-date=1 May 2012}}

In July 2010 a special issue of Astronomy and Astrophysics was published with 152 papers on initial results from the observatory.{{cite press release |url=http://www.aanda.org/index.php?option=com_content&view=article&id=588&Itemid=270&lang=en |title=A&A special feature: Herschel: the first science highlights |publisher=Astronomy & Astrophysics |date=16 July 2010 |access-date=1 May 2012 |id=ID# aa201003}}

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.{{cite web |url=http://www.aanda.org/index.php?option=com_toc&url=/articles/aa/abs/2010/13/contents/contents.html |title=Herschel/HIFI: first science highlights |work=Astronomy & Astrophysics |date=October 2010 |access-date=1 May 2012}}

It was reported on 1 August 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.{{cite journal |title=Herschel measurement of molecular oxygen in Orion |journal=Astrophysical Journal |volume=737 |issue=2 |last1=Goldsmith |first1=Paul F |last2=Liseau |first2=René |last3=Bell |first3=Tom A. |last4=Black |first4=John H. |last5=Chen |first5=Jo-Hsin |last6=Hollenbach |first6=David |last7=Kaufman |first7=Michael J. |last8=Li |first8=Di |last9=Lis |first9=Dariusz C.|last10=Melnick|first10=Gary |last11=Neufeld |first11=David |last12=Pagani |first12=Laurent |last13=Snell |first13=Ronald |last14=Benz |first14=Arnold O. |last15=Bergin |first15=Edwin |last16=Bruderer |first16=Simon |last17=Caselli |first17=Paola|author17-link=Paola Caselli |last18=Caux |first18=Emmanuel |last19=Encrenaz |first19=Pierre|last20=Falgarone|first20=Edith |last21=Gerin |first21=Maryvonne |last22=Goicoechea |first22=Javier R. |last23=Hjalmarson |first23=Åke |last24=Larsson |first24=Bengt |last25=Le Bourlot |first25=Jacques |last26=Le Petit |first26=Franck |last27=De Luca |first27=Massimo |last28=Nagy |first28=Zsofia |last29=Roueff |first29=Evelyne|last30=Sandqvist|first30=Aage |page=96 |date=August 2011 |doi=10.1088/0004-637X/737/2/96 |arxiv=1108.0441 |bibcode=2011ApJ...737...96G |s2cid=119289914 |display-authors=29}}{{cite journal |title=Molecular oxygen in the ρ Ophiuchi cloud |journal=Astronomy & Astrophysics |volume=466 |issue=3 |last1=Larsson |first1=B |last2=Liseau |first2=R. |last3=Pagani |first3=L. |last4=Bergman |first4=P. |last5=Bernath |first5=P. |last6=Biver |first6=N. |last7=Black |first7=J. H. |last8=Booth |first8=R. S. |last9=Buat |first9=V.|last10=Crovisier|first10=J. |last11=Curry |first11=C. L. |last12=Dahlgren |first12=M. |last13=Encrenaz |first13=P. J. |last14=Falgarone |first14=E. |last15=Feldman |first15=P. A. |last16=Fich |first16=M. |last17=Florén |first17=H. G. |last18=Fredrixon |first18=M. |last19=Frisk |first19=U.|last20=Gahm|first20=G. F. |last21=Gerin |first21=M. |last22=Hagström |first22=M. |last23=Harju |first23=J. |last24=Hasegawa |first24=T. |last25=Hjalmarson |first25=Å. |last26=Johansson |first26=L. E. B. |last27=Justtanont |first27=K. |last28=Klotz |first28=A. |last29=Kyrölä |first29=E.|last30=Kwok|first30=S. |pages=999–1003 |date=May 2007 |doi=10.1051/0004-6361:20065500 |arxiv=astro-ph/0702474 |bibcode=2007A&A...466..999L |s2cid=7848330 |display-authors=8}}

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.{{cite news |title=Comets take pole position as water bearers |journal=Nature |first=Ron |last=Cowen |date=5 October 2011 |doi=10.1038/news.2011.579}} On 20 October 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.{{cite press release |url=http://www.herschel.caltech.edu/index.php?SiteSection=News&NewsItem=nhsc2011-018 |title=Herschel Finds Oceans of Water in Disk of Nearby Star |publisher=Herschel Space Observatory |date=20 October 2011 |access-date=1 May 2012 |id=ID# nhsc2011-018 |archive-date=15 November 2013 |archive-url=https://web.archive.org/web/20131115030448/http://www.herschel.caltech.edu/index.php?SiteSection=News |url-status=dead }}

On 18 April 2013, the Herschel team announced in another Nature paper that it had located an exceptional starburst galaxy which produced over 2,000 solar masses of stars a year. The galaxy, termed HFLS3, is located at z = 6.34, originating only 880 million years after the Big Bang.{{Cite journal |title=A dust-obscured massive maximum-starburst galaxy at a redshift of 6.34 |journal=Nature |volume=496 |issue=7445 |first1=D. A. |last1=Riechers |first2=C. M. |last2=Bradford |first3=D. L. |last3=Clements |first4=C. D. |last4=Dowell |first5=I. |last5=Pérez-Fournon |first6=R. J. |last6=Ivison |first7=C. |last7=Bridge |first8=A. |last8=Conley |first9=H.|last10=Vieira|first10=J. D. |last11=Wardlow |first11=J. |last12=Calanog |first12=J. |last13=Cooray |first13=A. |last14=Hurley |first14=P. |last15=Neri |first15=R. |last16=Kamenetzky |first16=J. |last17=Aguirre |first17=J. E. |last18=Altieri |first18=B. |last19=Arumugam |first19=V.|last20=Benford|first20=D. J. |last21=Béthermin |first21=M. |last22=Bock |first22=J. |last23=Burgarella |first23=D. |last24=Cabrera-Lavers |first24=A. |last25=Chapman |first25=S. C. |last26=Cox |first26=P. |last27=Dunlop |first27=J. S. |last28=Earle |first28=L. |last29=Farrah |first29=D.|last30=Ferrero|first30=P. |last9=Fu |pages=329–333 |date=2013 |pmid=23598341 |doi=10.1038/nature12050 |arxiv=1304.4256 |bibcode=2013Natur.496..329R |s2cid=4428367 |display-authors=8}}

Just days before the end of its mission, ESA announced that Herschel{{'s}} observations had led to the conclusion that water on Jupiter had been delivered as a result of the collision of Comet Shoemaker–Levy 9 in 1994.{{cite news |url=http://www.astronomy.com/~/link.aspx?_id=52bdfb92-95a8-4a3f-b59b-bec66783bd79 |title=Herschel links Jupiter's water to comet impact |work=Astronomy |date=23 April 2013 |access-date=29 April 2013}}

On 22 January 2014, ESA scientists using Herschel data reported the detection, for the first definitive time, of water vapor on the dwarf planet, Ceres, largest object in the asteroid belt.{{cite journal |last1=Küppers |first1=Michael |last2=O’Rourke |first2=Laurence |last3=Bockelée-Morvan |first3=Dominique|author3-link=Dominique Bockelée-Morvan |last4=Zakharov |first4=Vladimir |last5=Lee |first5=Seungwon |last6=von Allmen |first6=Paul |last7=Carry |first7=Benoît |last8=Teyssier |first8=David |last9=Marston |first9=Anthony |last10=Müller |first10=Thomas |last11=Crovisier |first11=Jacques |last12=Barucci |first12=M. Antonietta |last13=Moreno |first13=Raphael |title=Localized sources of water vapour on the dwarf planet (1) Ceres |journal=Nature |volume=505 |issue=7484 |date=2014 |pages=525–527 |issn=0028-0836 |doi=10.1038/nature12918 |pmid=24451541 |bibcode=2014Natur.505..525K|s2cid=4448395 }}{{cite web |last1=Harrington |first1=J.D. |title=Herschel Telescope Detects Water on Dwarf Planet – Release 14-021 |url=http://www.nasa.gov/press/2014/january/herschel-telescope-detects-water-on-dwarf-planet |date=22 January 2014 |work=NASA |access-date=22 January 2014}} The finding is unexpected because comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids."

File:Animation of Herschel Space Observatory trajectory around Earth.gif }}]]

On 29 April 2013, ESA announced that Herschel{{'s}} supply of liquid helium, used to cool the instruments and detectors on board, had been depleted, thus ending its mission. At the time of the announcement, Herschel was approximately 1.5 million km from Earth. Because Herschel{{'s}} orbit at the L2 point is unstable, ESA wanted to guide the craft on a known trajectory. ESA managers considered two options:

• Place Herschel into a heliocentric orbit where it would not encounter Earth for at least several hundred years.
• Guide Herschel on a course toward the Moon for a destructive high-speed collision that would help in the search for water at a lunar pole. Herschel would take about 100 days to reach the Moon.{{cite news |url=http://www.spaceflightnow.com/news/n1210/26herschel |title=Scientists could aim derelict telescope for moon impact |work=Spaceflight Now |first=Stephen |last=Clark |date=26 October 2012 |access-date=2 May 2013}}

The managers chose the first option because it was less costly.{{cite news |url=http://www.universetoday.com/98932/herschel-spacecraft-wont-bomb-the-moon-but-grail-will/ |title=Herschel Spacecraft Won't 'Bomb' the Moon, But GRAIL Will |work=Universe Today |last=Atkinson |first=Nancy |date=11 December 2012 |access-date=4 May 2013}}

On 17 June 2013, Herschel was fully deactivated, with its fuel tanks forcibly depleted and the onboard computer programmed to cease communications with Earth. The final command, which severed communications, was sent from European Space Operations Centre (ESOC) at 12:25 UTC.

The mission's post-operations phase continued until 2017. The main tasks were consolidation and refinement of instrument calibration, to improve data quality, and data processing, to create a body of scientifically validated data.{{cite web |url=http://www.mpia-hd.mpg.de/IRSPACE/herschel/ |title=Infrared Space Astronomy: Herschel |publisher=Max-Planck-Institut für Astronomie |access-date=29 April 2013}}

Following Herschel{{'s}} demise, some European astronomers have pushed for the joint European-Japanese SPICA far-infrared observatory project, as well as ESA's continued partnership in NASA's James Webb Space Telescope.{{Cite web |url=http://jwst.nasa.gov/ |title=James Webb Space Telescope |publisher=NASA |access-date=29 May 2016}} James Webb covers the near-infrared spectrum from 0.6 to 28.5 μm, and SPICA covers the mid-to-far-infrared spectral range between 12 and 230 μm. While Herschel{{'s}} dependence on liquid helium coolant limited the design life to around three years, SPICA would have used mechanical Joule-Thomson coolers to sustain cryogenic temperatures for a longer period of time. SPICA's sensitivity was to be two orders of magnitude higher than Herschel.{{cite web |url=http://www.spica-mission.org/SPICA.html |title=The Sweet Spot: Spectroscopy from 12 to 230μm |publisher=SPICA project |date=7 April 2017 |access-date=9 July 2018}}

NASA's proposed Origins Space Telescope (OST) would also observe in the far-infrared band of light. Europe is leading the study for one of OST's five instruments, the Heterodyne Receiver for OST (HERO).{{cite web |url=https://smd-prod.s3.amazonaws.com/science-red/s3fs-public/atoms/files/Cooray-OST-overview-APAC-July02017.pdf |title=Origins Space Telescope |publisher=NASA |first=Asantha |last=Cooray |date=July 2017 |access-date=10 July 2018}}

{{Portal|Astronomy|Spaceflight}}

• Atacama Large Millimeter Array (ALMA)
• Spitzer Space Telescope
• List of largest infrared telescopes
• List of largest optical reflecting telescopes
• List of space telescopes

{{Reflist|30em}}

• {{cite journal |last=Harwit |first=M. |title=The Herschel Mission |journal=Advances in Space Research |volume=34 |issue=3 |pages=568–572 |date=2004 |doi=10.1016/j.asr.2003.03.026 |bibcode=2004AdSpR..34..568H}}
• {{cite journal |last=Dambeck |first=Thorsten |title=One Launch, Two New Explorers: Planck Readies to Dissect the Big Bang |journal=Sky and Telescope |volume=117 |issue=5 |pages=24–28 |date=May 2009}}

{{Commons category|Herschel (space telescope)}}

{{Wikinews|ESA launches Herschel Space Observatory and Planck Satellite}}

• ESA
• [http://www.esa.int/herschel/ Herschel mission website]
• [http://sci.esa.int/herschel/ Herschel science website]
• [http://www.esa.int/Our_Activities/Operations/Herschel Herschel operations website]
• [http://www.cosmos.esa.int/web/herschel Herschel science results website]
• NASA
• [http://www.nasa.gov/herschel/ Herschel mission website] {{Webarchive|url=https://web.archive.org/web/20221029182611/http://www.nasa.gov/herschel/ |date=29 October 2022 }}
• [http://www.herschel.caltech.edu/ Herschel Science Center]
• [http://irsa.ipac.caltech.edu/Missions/herschel.html NASA/IPAC Herschel archive]
• [http://herschel.cf.ac.uk/ United Kingdom outreach website]

{{Space observatories}}

{{European Space Agency}}

{{Jet Propulsion Laboratory}}

{{Orbital launches in 2009}}

{{Authority control}}

Category:European Space Agency space probes

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