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Herschel Space Observatory

By Wikipedia,
the free encyclopedia,

http://en.wikipedia.org/wiki/Herschel_Space_Observatory

Herschel Space Observatory
General information
NSSDC ID 2009-026A
Organization European Space Agency (ESA) with Thales Alenia Space as Prime contractor
Launch date 2009-05-14 13:12:02 UTC
Launched from Guiana Space Centre
French Guiana
Launch vehicle Ariane 5 ECA
Mission length elapsed:  1 month and 13 days
Mass 3,300 kg
Type of orbit Lissajous orbit
Orbit height 1.5 million km
Orbit period 1 year
Orbit velocity 7,500 m/s (27,000 km/h)
Location Lagrangian point L2
Telescope style Ritchey-Chrétien
Wavelength 60 to 670 µm (infrared)
Diameter 3,500 mm, f/0.5 [3.5 m]
Collecting area 9.6 m²
Focal length 28.5 m f/8.7
Instruments
HIFI Heterodyne Instrument for the Far Infrared
PACS Photodetector Array Camera and Spectrometer
SPIRE Spectral and Photometric Imaging Receiver
Website herschel.esac.esa.int

The Herschel Space Observatory is a space observatory from the European Space Agency (ESA). It was originally proposed in 1982 by a consortium of European scientists. The mission is named after Sir William Herschel, the discoverer of the infrared spectrum and planet Uranus.

Science

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

Instrumentation

The mission, formerly titled the Far Infrared and Sub-millimetre Telescope (FIRST), involves the first space observatory to cover the full far infrared and submillimetre waveband. At 3.5 meters wide, its telescope incorporates the largest mirror ever deployed in space. The light is focused onto three instruments with detectors kept at temperatures below 2 K (−271 °C). The instruments are cooled with liquid helium, boiling away in a near vacuum at a temperature of approximately 1.4 K (−272 °C). The 2,000-litre supply of helium on board the satellite will limit its operational lifetime, nonetheless it is expected to be operational for at least 3 years.

Herschel carries three detectors:

PACS (Photodetecting Array Camera and Spectrometer)
An imaging camera and low-resolution spectrometer covering wavelengths from 55 to 210 micrometres. The spectrometer has a spectral resolution between R=1000 and R=5000 and is able to detect signals as weak as −63dB. The imaging camera can image simultaneously in two bands (either 60–85/85–130 micrometres and 130–210 micrometres) with a detection limit of a few millijanskys.
SPIRE (Spectral and Photometric Imaging Receiver)
An imaging camera and low-resolution spectrometer covering 194 to 672 micrometre wavelength. The spectrometer has a resolution between R=40 and R=1000 at a wavelength of 250 micrometres and is able to image point sources with brightnesses around 100 millijanskys (mJy) and extended sources with brightnesses of around 500 mJy. The imaging camera has three bands, centered at 250, 350 and 500 micrometres, each with 139, 88 and 43 pixels respectively. It should be 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.
HIFI (Heterodyne Instrument for the Far Infrared)
A heterodyne detector which is able to electronically separate radiation of different wavelengths, giving a spectral resolution as high as R=10. The spectrometer can be operated within two wavelength bands, from 157 to 212 micrometres and from 240 to 625 micrometres.

Service Module – a common development for Herschel and Planck

A common service module (SVM) was designed and built by Thales Alenia Space in its Rome's plant, for the Herschel and Planck missions combined into one single program.

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

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

All spacecraft units on the SVM are redundant.

Power Subsystem

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.

Attitude and Orbit Control

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 satellite is three-axis stabilized, the absolute pointing error needs to be less than 3.7 arc sec.

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

Launch and orbit

The satellite, 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..

It is now on a very elliptical orbit (perigee: 270.0 km (intended 270.0±4.5), apogee: 1,197,080 km (intended 1,193,622±151,800), inclination 5.99 deg (intended 6.00±0.06)), on its way towards the second Lagrangian point.

On June 14, 2009, ESA successfully sent the command for the cryocover to open which will allow 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. Herschel is reported to have completed 90% of the distance to its orbit 1.5 million km away from Earth. Five days later the first set of test photos, depicting M51 Group, has been published by ESA.

In July 2009, approximately sixty days after launch, it is expected to enter a Lissajous 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.

See also

External links




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Published - July 2009














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