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Stargazing
They are working on one of the European
Space Agency’s challenges: to collect the light from six telescopes
in an optical fibre measuring just 1/50 mm. The goal is to find
signs of life in distant space.
Contact: Steinar
Neegård, SINTEF IKT
Tel: +47 73 59 10 43
E mail: steinar.neegard@sintef.no
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Ill.: MEDIALAB/©ESA
2002
The six ESA telescopes will retransmit
the
light signals to a common satellite, the «hub»,
orbiting in the centre of the flotilla of telescopes. The
hub satellite analyses the signals, which are then sent down
to Earth via a communications satellite.
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The fibre optic jigsaw puzzle is a small
but vitally important component in the ESA Darwin project, which
is looking for signs of life outside of our own solar system. Project
researchers are looking farther afield than Mars – the part
of space being investigated is several light years away from the
red planet recently conquered with space vehicle and camera. The
plan is to send into space an advanced remotecontrolled observatory
by 2015.
SPECTRUM ANALYSIS
The planets being studied are so far away that it would take about
one million years to travel there on today’s spacecraft. Researchers
are therefore using a technique called spectrum analysis in their
search for signs of life. In this case, that means analysing infrared
lights from the planets.
“Light is made up of electromagnetic
waves. The light’s infrared spectrum can tell us what substances
and gases are present on the planet,” says researcher Steinar
Neegård of SINTEF.
“Spectrum analyses can tell us if the
three prerequisites for life as we know it – water, carbon
dioxide and oxygen – exist somewhere out there.”
CATCHING LIGHT
One of the major challenges for the Darwin project is to capture
the light from the planets. This is difficult, in part because of
the luminous intensity of the stars and due to the enormous distance.
“In extremely simple terms,we can compare
the problem with trying to see stars when the sun is shining. We
won’t see the stars because the sunlight drowns out the light
from the starry sky,” explains Neegård. The enormous
distances make the objects, which in reality are located far apart,
appear to merge so that they look like one and the same point to
the naked eye.
“If our eye were to be able to distinguish
between a star and its planet in space, it would have to have a
lens with a diameter of at least 40 metres! Extremely large telescopes
can zoom far enough so that this becomes possible, but their size
and weight makes it impossible to send these out into space,”
says Neegård.
The telescope needs to be sent into space,
out of the Earth’s atmosphere, because heat radiated by the
Earth obscures these rays of light. At the same time, clouds obstruct
the rays the telescope is trying to capture. Sending out six satellites,
each with its own one-metre telescope, will solve the problem. The
ESA telescopes will hover in formation 50-200 metres apart and send
light signals to a combined satellite called HUB. The light will
be analysed using a method called nulling interferometry. The method
enables researchers to see possible planets, in spite of the proximity
of the much larger and brighter stars.
A NEEDLE’S EYE
The light signals from the six large telescopes need to enter a
tiny fibre optic cable in the HUB, to allow for spectrum analysis.
The light connection to the fibre needs to be made with minimal
loss of light – in this context, the loss of light rays is
like losing an important clue. Satellite vibrations, large temperature
differences between the sunny and shady side of the telescope, and
cosmic radiation make the light connection a huge challenge.
The fibre’s capability to filter out
noise from the signals, called spatial filtering, is critical in
the quality of the spectrum analysis. Neegård and his collaborators
at Kongsberg Defence and Aerospace (KDA) have proposed a completely
new solution for this complex signal transmission problem. They
have developed a concept to ‘get the camel through the eye
of a needle’ – a combined ray collector and ray former.
In practice, this device cleverly rearranges the light rays with
the help of an advanced mirror system. This distributes the light
so that most of the light from the telescope can be connected in
a fibre optic cable thinner than a strand of hair.
PATENT PENDING
The results to date show a 60 percent improvement in the light connection
between the two units. It is so promising that the Norwegian developers
have sought to patent their invention. In this context, 60 percent
is meaningful, so ESA is more than curious about how it will function
in practice. More light will speed the search, because more stars
and planets can be investigated, says Neegård. When the analysis
of the signals is completed in the HUB, the information is sent
back to Earth by radio beams. The long-term aim of KDA and SINTEF
is to deliver flight hardware to Darwin. Before the Norwegian technology
reaches that point, a variety of analysis and tests, together with
a technology demonstrator, need to be submitted to the ESA.
Christina B. Winge
| FAR
OFF |
| The distance to
the closest stars to be studied by ESA is more than four lightyears.
A light year is the distance travelled by light in the course
of a year, i.e. the speed of light (300,000 km/s) multiplied
by the number of seconds in a year (31,536,000), which comes
to about 10,000,000,000,000 km.
For the sake of comparison, a space shuttle travelling at
a speed of 28,000 kph would take nearly a million years to
reach Vega, which is 25.3 light years from the Earth. |
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