 Model of the Herschel Observatory | |||||||||
| Names | Far Infrared and Submillimetre Telescope | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Mission type | Space telescope | ||||||||
| Operator | ESA / NASA | ||||||||
| COSPAR ID | 2009-026K | ||||||||
| SATCATno. | 34937 | ||||||||
| Website | www | ||||||||
| Mission duration | Planned: 3 years Final: 4 years, 1 month, 2 days[1] | ||||||||
| Spacecraft properties | |||||||||
| Manufacturer | Thales Alenia Space | ||||||||
| Launch mass | 3,400 kg (7,500 lb)[2] | ||||||||
| Payload mass | Telescope: 315 kg (694 lb)[2] | ||||||||
| Dimensions | 7.5 m × 4.0 m (25 ft × 13 ft)[2] | ||||||||
| Power | 1 kW | ||||||||
| Start of mission | |||||||||
| Launch date | 14 May 2009, 13:12:02 UTC (2009-05-14UTC13:12:02) | ||||||||
| Rocket | Ariane 5 ECA | ||||||||
| Launch site | Guiana Space Centre, French Guiana | ||||||||
| Contractor | Arianespace | ||||||||
| End of mission | |||||||||
| Disposal | Decommissioned | ||||||||
| Deactivated | 17 June 2013, 12:25 UTC (2013-06-17UTC12:26)[3] | ||||||||
| Orbital parameters | |||||||||
| Reference system | L2 point 1,500,000 km (930,000 mi) | ||||||||
| Regime | Lissajous | ||||||||
| Main telescope | |||||||||
| Type | Ritchey–Chrétien | ||||||||
| Diameter | 3.5 m (11 ft) f/0.5 (primary mirror)[4] | ||||||||
| Focal length | 28.5 m (94 ft) f/8.7[4] | ||||||||
| Collecting area | 9.6 m2 (103 sq ft) | ||||||||
| Wavelengths | 55 to 672 μm (far infrared) | ||||||||
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 ESA astrophysics insignia forHerschel | |||||||||
TheHerschel Space Observatory was aspace observatory built and operated by theEuropean Space Agency (ESA). It was active from 2009 to 2013, and was the largestinfrared telescope ever launched until the launch of theJames Webb Space Telescope in 2021.[5] Herschel carries a 3.5-metre (11.5 ft) mirror[5][6][7][8] and instruments sensitive to thefar infrared andsubmillimetre wavebands (55–672 μm). Herschel was the fourth and final cornerstone mission in theHorizon 2000 programme, followingSOHO,Cluster II,XMM-Newton andRosetta.
The observatory was carried into orbit by anAriane 5 in May 2009, reaching thesecond Lagrangian point (L2) of theEarth–Sun system, 1,500,000 kilometres (930,000 mi) from Earth, about two months later. Herschel is named afterSir William Herschel, the discoverer of theinfrared spectrum and planetUranus, and his sister and collaboratorCaroline Herschel.[9]
The observatory was 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.[10] The observatory sifted 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 telescope's lifespan was governed by the amount ofcoolant available for its instruments; when that coolant ran out, the instruments would stop functioning correctly. At the time of its launch, operations were estimated to last 3.5 years (to around the end of 2012).[11] It continued to operate until 29 April 2013 15:20 UTC, whenHerschel ran out of coolant.[12]
NASA was a partner in the Herschel mission, with US participants contributing to the mission; providing mission-enabling instrument technology and sponsoring the NASA Herschel Science Center (NHSC) at theInfrared Processing and Analysis Center and the Herschel Data Search at theInfrared Science Archive.[13]
In 1982 theFar Infrared and Sub-millimetre Telescope (FIRST) was proposed toESA. The ESA long-term policy-plan "Horizon 2000", produced in 1984, called for aHigh Throughput Heterodyne Spectroscopy mission as one of its cornerstone missions. In 1986, FIRST was adopted as this cornerstone mission.[14] 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 theInfrared 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.[15] Herschel was launched in 2009.
The Herschel mission cost€1,100 million.[16] This figure includes spacecraft and payload, launch and mission expenses, and science operations.[17]
Herschel specialised in collectinglight from objects in theSolar System as well as theMilky Way and evenextragalactic objects billions oflight-years away, such as newborngalaxies, and was charged with four primary areas of investigation:[18]
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".[19]
The mission involved the firstspace observatory to cover the fullfar infrared andsubmillimetre waveband.[18] At 3.5 metres wide (11 ft), Herschel carried the largest optical telescope ever deployed in space.[20] It was made not from glass but fromsinteredsilicon carbide. The mirror's blank was manufactured by Boostec inTarbes,France; ground and polished by Opteon Ltd. inTuorla Observatory,Finland; and coated by vacuum deposition at theCalar Alto Observatory inSpain.[21]
The light reflected by the mirror was focused onto three instruments, whose detectors were kept at temperatures below 2 K (−271 °C).[22] The instruments were cooled with over 2,300 litres (510 imp gal; 610 US gal) ofliquid helium, boiling away in a near vacuum at a temperature of approximately 1.4 K (−272 °C). The supply of helium on board the spacecraft was a fundamental limit to the operational lifetime of the space observatory;[8] it was originally expected to be operational for at least three years.[23]
Herschel carried three detectors:[24]
NASA developed and built the mixers, local oscillator chains and power amplifiers for this instrument.[30] TheNASA 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.[31]
A commonservice module (SVM) was designed and built byThales Alenia Space in itsTurin plant for the Herschel andPlanck missions, as they were combined into one single program.[32]
Structurally, the Herschel andPlanck 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 theavionics 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 thesolar array, employing triple-junctionsolar cells, abattery 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 theSun'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 andPlanck payload.
The Herschel spacecraft isthree-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 thestar tracker.
The spacecraft, built in theCannes Mandelieu Space Center, underThales Alenia Space Contractorship, was successfully launched from theGuiana Space Centre in French Guiana at 13:12:02 UTC on 14 May 2009, aboard anAriane 5 rocket, along with thePlanck spacecraft, and placed on a very elliptical orbit on its way towards thesecond Lagrangian point.[33][34][35] The orbit'sperigee was 270.0 km (intended270.0±4.5),apogee 1,197,080 km (intended1193622±151800),inclination 5.99 deg (intended6.00±0.06).[36]
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.[37]
Five days later the first set of test photos, depictingM51 Group, was published by ESA.[38]
In mid-July 2009, approximately sixty days after launch, it entered ahalo orbit of 800,000 km average radius around thesecond Lagrangian point (L2) of theEarth-Sun system, 1.5 million kilometres from the Earth.[35][39]
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.[35]
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 adark nebula, in the area ofNGC 1999 shed new light in the way newly forming star regions discard the material which surround them.[40]
In July 2010 a special issue ofAstronomy and Astrophysics was published with 152 papers on initial results from the observatory.[41]
A second special issue ofAstronomy 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.[42]
It was reported on 1 August 2011, that molecularoxygen 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 theOdin team.[43][44]
An October 2011 report published inNature states that Herschel's measurements of deuterium levels in the cometHartley 2 suggests that much of Earth's water could have initially come from cometary impacts.[45] 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 theorigin of water on Earth.[46]
On 18 April 2013, the Herschel team announced in anotherNature paper that it had located an exceptionalstarburst galaxy which produced over 2,000solar masses of stars a year. The galaxy, termedHFLS3, is located atz = 6.34, originating only 880 million years after theBig Bang.[47]
Just days before the end of its mission, ESA announced that Herschel's observations had led to the conclusion that water onJupiter had been delivered as a result of the collision ofComet Shoemaker–Levy 9 in 1994.[48]
On 22 January 2014,ESA scientists using Herschel data reported the detection, for the first definitive time, ofwater vapor on thedwarf planet,Ceres, largest object in theasteroid belt.[49][50] The finding is unexpected becausecomets, notasteroids, 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."[50]
On 29 April 2013, ESA announced that Herschel's supply ofliquid helium, used to cool the instruments and detectors on board, had been depleted, thus ending its mission.[12] 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:
The managers chose the first option because it was less costly.[52]
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 fromEuropean Space Operations Centre (ESOC) at 12:25 UTC.[3]
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.[53]
Following Herschel's demise, some European astronomers have pushed for the joint European-JapaneseSPICA far-infrared observatory project, as well as ESA's continued partnership in NASA'sJames Webb Space Telescope.[12][54] 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 mechanicalJoule-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.[55]
NASA's proposedOrigins Space Telescope (OST) would also observe in thefar-infrared band of light. Europe is leading the study for one of OST's five instruments, the Heterodyne Receiver for OST (HERO).[56]
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