Herschel Space Observatory was a space based telescope that was 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 was the fourth Cornerstone mission in the European Space Agency’s Horizon 2000 program. Alcatel Space was the prime contractor for ESA’s Herschel. The subcontractors involved in this contract covered all 15 European countries which are members of ESA, including Portugal which participated for the first time in an ESA scientific project. The project also involved 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 operated independently.
The European Space Agency’s Herschel Space Observatory had the largest mirror ever built for a space telescope at the time of launch. At 3.5-metres in diameter the mirror collected long-wavelength radiation from some of the coldest and most distant objects in the Universe. In addition, Herschel was the only space observatory to cover a spectral range from the far infrared to sub-millimetre. It revealed 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 was to:
- Study the formation of galaxies in the early universe and their subsequent evolution
- Investigate the creation of stars and their interaction with the interstellar medium
- Observe the chemical composition of the atmospheres and surfaces of comets, planets and satellites
- Examine the molecular chemistry of the universe
Herschel’s operational orbit was 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 avoided problems caused by infrared radiation from the Earth interfering with observations. The L2 orbit also prevented 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 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:
- HIFI(Heterodyne Instrument for the Far Infrared), a very high resolution heterodyne spectrometer
- PACS(Photodetector Array Camera and Spectrometer) – an imaging photometer and medium resolution grating spectrometer
- 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
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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