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Herschel overview 
Objective Herschel will investigate the history of how stars and galaxies formed and to study how they continue to form in our own and other galaxies. Herschel will observe at wavelengths never covered before.
For more in-depth scientific and technical details of our Space Science Programme and missions, follow this link.
Herschel will be the largest space telescope of its kind when launched. Herschel's 3.5-metre diameter mirror will collect long-wavelength infrared radiation from some of the coolest and most distant objects in the Universe. Herschel will be the only space observatory to cover the spectral range from far-infrared to sub-millimetre wavelengths. Infrared radiation is invisible for the human eye. It is actually 'heat', or thermal radiation. Even objects that we think of as being very cold, such as an ice cube, emit infrared radiation. For this reason, infrared telescopes can observe astronomical objects that remain hidden for optical telescopes, such as cool objects that are unable to emit in visible light. Also, infrared instruments need to be cooled down to temperatures very close to absolute zero (-273.15°C), otherwise their own infrared emission would spoil the observations. Opaque objects, those surrounded by clouds of dust, are another speciality for infrared telescopes: the longer infrared wavelengths can penetrate the dust, allowing us to see deeper into such clouds.
However, Earth's atmosphere acts as an 'umbrella' for most infrared wavelengths, preventing them from reaching the ground. A space telescope is needed to detect this kind of radiation invisible to the human eye and to optical telescopes.
What's special? If it was possible to look at the Universe from the outside it would probably appear as a foamy structure, with the galaxies distributed in curved walls surrounding huge areas of emptiness, like bubbles in a foam bath. Such is the overall picture of the present-day Universe. However, it was not always like that. There was a time when galaxies were not there, simply because they did not even exist yet. Astronomers have several questions about this time. When did galaxies form? How did it happen? Did they all form at about the same time, or is there a non-stop galaxy-making machine at work? Were the first galaxies like those we see now? The galaxies are made of stars... Did the stars form first and then get together to form galaxies, or was it the other way round? How do stars form? When they form, do they normally form planets as well? Astronomers dream of a telescope able to answer these kinds of questions. They want a telescope that fulfils at least two requirements. It has to be a giant space telescope, able to collect light from very distant galaxies. Secondly, it must be able to observe objects completely enshrouded by dust, as forming stars and galaxies are certainly dusty.
ESA's Herschel mission has been designed specifically to achieve these goals. With its ability to detect far-infrared light, it will let astronomers see, for the first time, dusty and cold regions that have been hidden so far. With its 3.5-metre mirror, Herschel will mark the beginning of a new generation of 'space giants'.
The Herschel satellite is a tall 'tube' 7.5 metres high and 4 metres wide, with a launch mass of around 3.3 tonnes. It will carry the infrared telescope and three scientific instruments. The bulk of the spacecraft consists of a liquid helium thermos bottle inside which the instrument detectors sit and are cooled down to only a few degrees above absolute zero. The telescope is a Cassegrain telescope, with a primary mirror diameter of 3.5 metres. This is the largest space telescope ever to be built and a great technological challenge that Europe will face alone. The contract signed between ESA and Astrium in Toulouse, France, to build Herschel's telescope makes it fully European. Herschel's telescope has to meet demanding requirements. It has to be light enough to be placed into an orbit far more distant than, for example, that of Hubble. Also, the mirror's surface has to be extremely smooth; it had to be polished to make it so uniform that its 'bumps' are smaller than a few thousandths of a millimetre. It will have to withstand very hard environmental conditions. At launch, it will be 'shaken' with a force several times that of normal gravity on Earth.
In order to achieve its scientific objectives, Herschel's detectors have to operate at very low and stable temperatures. So the spacecraft is equipped with the means of cooling the detectors close to absolute zero (-273ºC), ranging from -265ºC to only a few tens of a degree above absolute zero.
Science payload Herschel's science payload consists of three instruments:
Herschel will be launched atop an Ariane rocket in spring 2009 with another satellite, Planck, which will study the cosmic microwave background radiation. The launch slot begins on 10 April 2009 and lasts for four weeks; the date will be decided at the beginning of 2009. The two spacecraft will separate about 2.5 hours after launch and will operate independently. In less than six months, Herschel will reach its operational orbit around a point in space known as the second Lagrangian point (L2), situated at 1.5 million kilometres away from the Earth.
Herschel has been designed to perform routine science operations for a minimum of 3 years at L2. The mission will end when the helium used to cool the focal plane of the scientific instruments is depleted. History The main scientific emphasis, mission requirements, and technological needs for Herschel (or FIRST as it was then called) were discussed for the first time in the early 1980s. In 1983, the United States-Dutch-British IRAS satellite inaugurated infrared space astronomy by mapping 250 000 cosmic infrared sources and large areas of extended emission. In November 1995, ESA launched its Infrared Space Observatory (ISO) which has allowed a much closer look, a more detailed perception of the 'infrared scenery'. In August 2003, NASA launched the Spitzer Space Telescope (formerly Space Infrared Telescope Facility, SIRTF), a space-borne, cryogenically cooled infrared observatory. In February 2006, JAXA launched AKARI, a new infrared mission with ESA participation. Spitzer and AKARI are currently operating. As ESA's fourth Cornerstone mission, Herschel has been planned to build on and extend the successes of these missions by offering a much larger telescope and being the first to extend the spectral coverage down into the far-infrared and sub-millimetre wavelengths. Partnership The Prime Contractor for the Herschel satellite is Thales Alenia Space Industries (Cannes, France), leading a consortium of industrial partners with Astrium (Friedrichshafen, Germany) responsible for the Extended Payload Module (EPLM) and the Thales Alenia Space industry branch of Torino, Italy, responsible for the Service Module (SVM). There is also a host of subcontractors spread throughout Europe. PACS was designed and built by a Consortium (led by MPE, Garching, Germany) of scientists and institutes - under their own funding - from Germany, Belgium, Austria, France, Italy, and Spain. SPIRE was designed and built by a Consortium (led by University of Wales (Cardiff, United Kingdom) of scientists and institutes - under their own funding - from the United Kingdom, France, Canada, China, Italy, Spain, Sweden, and USA.
HIFI was designed and built by a Consortium (led by SRON, Groningen, The Netherlands) of scientists and institutes - under their own funding - from The Netherlands, France, Germany, and USA, Canada, Ireland, Italy, Poland, Russia, Spain, Sweden, Switzerland, and Taiwan.
Last update: 19 August 2009
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