A BIG space-based infra-red scope
- From: Rich <none@xxxxxxxx>
- Date: Tue, 27 Sep 2005 23:13:20 -0400
Reflections In The World's Largest Space Mirror
Much of our Universe has long remained invisible. Our eyes perceive
only a fraction of the electromagnetic spectrum. Seeing at infrared
wavelengths, for instance, allows astronomers to explore hidden
celestial objects and processes such as the birth of stars. In two
years, they will be able to use the most powerful of all infrared
space telescopes, Herschel.
The latest edition of the Euronews 'Space' magazine recently had the
privilege of seeing Herschel's spectacular telescope, a jewel of
precision and high technology, with the largest primary mirror ever to
be launched into space. The venue was the Intespace satellite test
facility in Toulouse, located along the banks of the Canal du Midi
which flows through the town.
ESA's next-generation infrared observatory, due to be launched in
2007, follows in a grand tradition. In the 1980s, the US-Dutch-British
satellite IRAS inaugurated infrared space astronomy by mapping 250 000
cosmic infrared sources and large areas of extended emission. ESA's
ISO, launched in 1995, pursued this exploration providing a wealth of
science data until May 1998, well beyond its nominal 18-month
lifetime.
Currently NASA's Spitzer Space Telescope is in operation going further
down the ISO track. Software tools developed for Spitzer will be used
by Herschel that, in turn, will be pushing back the frontiers of
infrared astronomy with its larger telescope and ability to observe at
longer wavelengths.
While the satellite itself is under the responsibility of Alcatel
Space, EADS Astrium in Toulouse is the prime contractor for the
telescope, under direct contract to ESA. Over the past weeks, EADS
Astrium engineers have been putting the telescope through mechanical
qualification tests.
These have been conducted in conditions of pristine cleanliness to
avoid any risk of the mirror being tainted by condensation, dust
particles or molecular contamination.
On its support stand, the mirror offered multiple reflections of the
engineers working around it. Among them, Yves Toulemont, Herschel
Project manager at EADS Astrium, is justifiably proud of the very
impressive but remarkably lightweight dish.
"By comparison, Hubble has a primary mirror which is 2.4 metres in
diameter, and it had a telescope mass of 1500 kilograms. Our telescope
with a 3.5 metre mirror is considerably larger, but has a mass of only
320 kilograms."
The telescope has required the use of the most advanced technologies.
The primary mirror is an assembly of twelve petals, seamlessly joined
together. The mirror structure is composed of a ceramic wafer of
silicon carbide, which is less than four millimetres thick, but very
resistant to the mechanical and thermal stresses encountered during
launch and in orbit. It has been polished to a precision of better
than three micrometres.
The secondary mirror has also been made of silicon carbide and has
been polished to a precision better than one micrometre. Both ceramic
mirrors are coated with a thin layer of aluminium providing the actual
reflective surface.
At seven metres long, Herschel will have a launch mass of just over
three tonnes. The bulk of the spacecraft consists of a 'cryostat', a
giant liquid-helium cooled 'thermos' bottle. In it are placed all the
detectors of the three science instruments sitting on top. These are
receiving the infrared radiation collected by the mirror and will be
kept at a temperature of below minus 271 Celsius.
Herschel will be launched by an Ariane 5 in the second half of 2007,
together with ESA's Planck satellite that will study cosmic microwave
background radiation. The two spacecraft will then separate and
Herschel will be positioned to orbit a special point in space, called
the L-2 Lagrangian point.
"The so-called L-2 Lagrangian point is located 1.5 million kilometres
away from Earth in a direction diametrically opposite to the Sun,"
explains Yves Toulemont. "It is special because the satellite will be
in a fixed position, relative to the Sun and Earth."
"Both will be in the same area of the sky as seen from Herschel, thus
offering an uninterrupted view of the Universe." The observatory will
of course never look in the Sun's direction or at any other bright
object, to avoid damaging its sensitive detectors.
Herschel will be the first space observatory to cover the range from
far infrared to sub-millimetre wavelengths. "The telescope will not
only allow us to view the invisible Universe through this window, but
we will be gather a maximum of infrared radiation, collecting light
from newborn galaxies thousands of millions of light-years away,"
explains Giovanni Bignami, chairman of ESA Space Science Advisory
Committee, and also director of France's Centre d'Etude Spatiale des
Rayonnements (CESR).
"Herschel will be able to search for very special radiation, produced
by the vibration of molecules, such as water and those of more complex
organic ones. Finding these may not be proof of the existence of life,
but at least the presence of its constituents."
By delving into the molecular composition of the Universe, tracing
back the history of the birth of stars and understanding the formation
and evolution of galaxies, astronomers will pursue these
investigations begun with IRAS and ISO. The teams building the
Herschel observatory and its giant mirror are confident of fulfilling
their expectations.
EuroNews is a key medium for delivering international information with
a European point of view. Broadcast in 79 countries, EuroNews reaches
144 million households in Europe, the Middle East, Africa, Central
Asia and North and Latin America via cable, digital satellite and
through terrestrial channels. This Space Magazine is produced and
broadcast every two weeks, with a new programme starting every second
Friday. Each magazine is four minutes long and broadcast 21 times in
one week, including evening prime time on Fridays and Saturdays, in
order to reach a maximum audience.
Copyright 2005 by Space Daily, Distributed United Press
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