http://www.sciencedaily.com/releases/2007/04/070412100834.htm

Search For Extrasolar Planets And Extraterrestrial Life Improved With
Darwin's Frictionless Optics

Science Daily - ESA's Darwin mission will look for extrasolar planets and
signs of life. The Agency's Technology Research Programme has sponsored the
development of critical optical components whose frictionless mechanism can
respond to the touch of a feather.

Darwin will combine light from four or five telescopes and send it down to
Earth. ESA has a strategy to enable more sophisticated searches for
extra-solar planets in the future. Two planned developments rely on
combining the light from a number of different telescopes. Both could
greatly benefit from this technology. (Credit: ESA 2002)
ESA's Darwin mission aims to discover extrasolar planets and examine their
atmospheres for signs of life, particularly for the presence of certain
life-related chemicals such as oxygen and carbon dioxide. The major
technical challenge lies in distinguishing, or resolving, the light from an
extrasolar planet from the hugely overwhelming radiation emitted by the
planet's nearby star.

The multi-satellite Darwin mission will use optical interferometry in which
at least three separate orbiting telescopes jointly operate as an equivalent
single telescope with a much larger effective aperture, thus achieving the
required resolution. With this method, multiple smaller telescopes having
actual apertures of, for example, 3 metres, can combine to provide an
effective aperture of several tens to hundreds of metres, depending on the
distance between the individual telescopes.

Creating delicate phase delays

Darwin will use nulling interferometry, a specific interferometric technique
used to shield the overwhelming star emissions by precisely delaying the
radiation coming from some of the telescopes by a small amount. This, in
combination with achromatic - or colour independent - phase shifters, will
cancel out the bright star radiation while allowing the much fainter
extrasolar planet light to be detected.

A component known as an Optical Delay Line (ODL) is at the core of such
interferometric observations. An ODL is a sophisticated opto-mechanical
device that can introduce well-defined variations, or delays, in the optical
path of a light beam and includes a moving mirror positioned with extremely
good accuracy.

Precise movement using magnetic levitation

To demonstrate the critical technology required by Darwin, ESA's Technology
Research Programme has sponsored the design and testing of an ODL that uses
magnetic levitation for precise, frictionless mirror movement. The ODL's
wonderfully sophisticated guidance and translation mechanism is, thanks to
the magnetic levitation, completely contactless and frictionless and can be
easily displaced by the faint touch of a feather (see video clip
accompanying article).

The optical delay introduced by the ODL must be capable of adjusting the
optical path length of collected light beams with an accuracy of a few
nanometers; 1 nanometre corresponds to a millionth of a millimetre.

Under ESA sponsorship, the ODL was built by an industrial consortium led by
TNO Science and Industry, part of The Netherlands' Organisation for Applied
Scientific Research, and including SRON and Dutch Space in the Netherlands,
Belgium's Micromega-Dynamics s.a. and the Centre Spatial de Liège, and
France's Alcatel Alenia Space and Sageis CSO. The ODL magnetic suspension
technology was pre-developed by Micromega-Dynamics under the ESA-funded MABE
(Magnetic Bearing) research study, which included quasi-zero gravity testing
during parabolic flights.

Sub-nanometre resolution to be incorporated in future flight mechanism

The ODL shown here successfully demonstrated sub-nanometre resolution and
stability; the design, materials and manufacturing processes for this ODL
are representative of a future flight-capable mechanism.

The ODL has also been thoroughly tested in Darwin's demanding cryogenic
environment, at 40 Kelvin - or about -233 Celsius.

Darwin's ODLs are uniquely engineered to operate at cryogenic temperatures
to avoid self-interference from the satellites' own thermal radiation. This
is mandatory as Darwin will conduct observations at mid-infrared
wavelengths, where the planet-to-starlight brightness ratio is relaxed
compared to that in visible wavelengths, and where life-related marker
chemicals such as water, ozone and carbon dioxide can be detected.

The ODLs will be used in Darwin for co-phasing the light collected by the
separate telescopes within a central hub spacecraft, which is responsible
for the correct recombination of the light beams and hence achieving the
high-performance resolution of a single very large telescope.

Note: This story has been adapted from a news release issued by European
Space Agency.

-- 

Ken

"Buddhism elucidates why we are sentient."
"Buddhism follows thought throughout the Universe."
"Karma means that you don't get away with anything."