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Herschel Space
Observatory is a space based telescope that is studying the
Universe by the light of the far-infrared and submillimeter
portions of the spectrum.
It was originally called Far
Infrared and Sub-millimetre Telescope or FIRST and was renamed
in honour of the pioneering astronomers William and Caroline
Herschel. It
was launched on 14 May 2009.
Herschel is the
fourth Cornerstone mission in the European Space Agency's Horizon 2000 program.
Alcatel Space is the prime contractor for ESA's Herschel. The subcontractors
involved in this contract will cover all 15 European countries which are members
of ESA, including Portugal which participates for the first time in an ESA
scientific project. The project also involves the United States.
An Ariane-5 launcher carried Herschel into space
on 14 May 2009. For reasons of cost effectiveness, ESA had decided to launch
Herschel together with Planck, a mission to study the cosmic microwave
background radiation. The two spacecraft separated soon after launch and
operate independently.
The Mission:
The European Space Agency's Herschel Space Observatory has the largest
mirror ever built for a space telescope. At 3.5-metres in diameter the mirror
will collect long-wavelength radiation from some of the coldest and most distant
objects in the Universe. In addition, Herschel will be the only space
observatory to cover a spectral range from the far infrared to sub-millimetre.
It is expected to
reveal new information about the earliest, most distant stars and galaxies, as
well as those closer to home in space and time.
The aim of the Herschel Space Observatory is to:
1. Study the formation of galaxies in the early universe and
their subsequent evolution
2. Investigate the creation of stars and their interaction with the interstellar
medium
3. Observe the chemical composition of the atmospheres and surfaces of comets,
planets and satellites
4. Examine the molecular chemistry of the universe
Herschel's operational orbit is located 1.5 million kilometres
away from the Earth in a direction diametrically opposite the Sun, at the second
Lagrange point of the Sun-Earth system (L2). By orbiting at L2, some 1.5
million kilometres from Earth, Herschel will avoid problems caused by infrared
radiation from the Earth interfering with observations. The L2 orbit also
prevents the occurrence of temperature changes due to the spacecraft moving in
and out of eclipse in an Earth orbit, which are a particular problem for
infrared instruments requiring extreme thermal stability.
Commencing about six months after launch it will offer three
years of routine science observations. It will be available for the worldwide
scientific community, with roughly two thirds of the observing time being 'open
time', which will be allocated through a standard competitive proposal
procedure.
The Spacecraft
The Herschel spacecraft is approximately 7.5 metres high and 4 x
4 metres in overall cross section, with a launch mass of around 3.3 tonnes. The
spacecraft comprises a service module, which houses systems for power
conditioning, attitude control, data handling and communications, together with
the warm parts of the scientific instruments, and a payload module. The payload
module consists of the telescope, the optical bench, with the parts of the
instruments that need to be cooled, i.e. the sensitive detector units and
cooling systems. The payload module is fitted with a sunshield, which protects
the telescope and cryostat from solar visible and infrared radiation and also
prevents Earth straylight from entering the telescope. The sunshield also
carries solar cells for the electric power generation.
The Telescope and Instruments
The Herschel telescope is a
Cassegrain design with a primary mirror diameter of 3.5 metres, the largest ever
built for use in space. The three scientific instruments are:
1. HIFI (Heterodyne
Instrument for the Far Infrared),
a very high resolution heterodyne spectrometer
2. PACS (Photodetector
Array Camera and Spectrometer)
- an imaging photometer and medium resolution grating spectrometer
3. SPIRE (Spectral
and Photometric Imaging Receiver)
- an imaging photometer and an imaging Fourier transform spectrometer
The instruments have been designed to
take maximum advantage of the characteristics of the Herschel mission. In order
to make measurements at infrared and sub-millimetre wavelengths, parts of the
instruments have to be cooled to near absolute zero. The optical bench, the
common mounting structure of all three instruments, is contained within the
cryostat and over 2000 litres of liquid helium will be used during the mission
for primary cooling. Individual instrument detectors are equipped with
additional, specialised cooling systems to achieve the very lowest temperatures.
Specs of
Spacecraft:
Mass:
3300 kg at launch
Dimensions:
9m high, 4m x 4m overall cross section
Mission Lifetime
- 3 years nominal from end of commissioning phase
Wavelength
- Infrared: 60 to 670 µm
Operations Centre
The European Space Operations
Control Centre (ESOC) in Darmstadt will communicate with the
spacecraft via a ground station near Perth, Australia.
Did you know?
Herschel is the only space facility ever developed
to cover the far infrared to sub-millimetre parts of the spectrum (from 60 to
670 µm). It will open up an almost unexplored part of the spectrum, which cannot
be observed well from the ground.
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Herschel Space Observatory
Links:
ESA Science & Technology -: Herschel:
ESA site
Herschel Science Centre:
Herschel Mission: by
NASA Jet Propulsion Laboratory
Herschel / Pacs: Source of Picture.
Also info on PACS
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comments or suggestions, then click
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Info.
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