Schott: Observatory Inside A Jumbo Jet
A flying telescope will be forging ahead to the limits of the Earth's atmosphere. From here, astronomers hope to gain a clear view of the universe."Beyond the clouds...", the view must be boundless - Astrophysicists perhaps had this popular German chanson in mind when they came up with the idea of building a large telescope that weighs tons into a jumbo jet. The joint project of NASA and the German Aerospace Center (DLR) has been named SOFIA, which stands for Stratospheric Observatory For Infrared Astronomy. The objective is to obtain an unclouded view of the stars and galaxies in aerial heights.
Many of the device's components have already been installed and are now being tested. This also applies to the "heart" of the flying observatory, a large, round mirror substrate made of Zerodur® glass ceramic from SCHOTT. With its 2.7 meter diameter, it is even larger than the Hubble Space Telescope. However, with a weight of 850 kilograms, the mirror brings only a fraction of the weight of the passengers that the former commercial aircraft used to hold onto the scale.
Lightweight mirror
The reconstructed 747 SP (Special Performance) is a truncated version
of the jumbo jet that had been flying for various airlines. To make
sure it would not drop down at the stern, due to its unusual load, a
delicate, honeycomb-shaped lightweight only 35 centimeters in thickness
was ground out of the glass ceramic substrate that weighed tons. This
reduction measure saves kerosene during flights and is easy on costs
and the environment.
The decision to use Zerodur® glass ceramic as the mirror substrate
material was hardly a difficult one for the engineers and technicians.
After all, this precise polished glass ceramic retains its shape, even
under extreme conditions at altitudes of up to 13,000 meters. "Here in
the stratosphere, several kilometers above the flight routes of
commercial airlines, there are icy temperatures of minus 60 degrees
Celsius", says Dr. Thorsten Doehring, Project Manager Astro/Space from
SCHOTT. Due to the stability of shape, the images of objects in space
always remain pin sharp.
Successful maiden flight
On April 26, 2007, the very first flight took place for the modified
aircraft in Texas. "The integration of the telescope represented a
major challenge for all those involved," explains SOFIA project
manager, Dr. Dietmar Lilienthal from the DLR, who has nothing in common
with his famous namesake, Otto Lilienthal, an aviation pioneer, except
the same mentality. "SOFIA and the telescope that was developed in
Germany survived their maiden flight very well," adds Professor
Hans-Peter Röser from the SOFIA Institute in Stuttgart (Germany). This
was also good news for MT-Mechatronics GmbH, based in Mainz, and
Kayser-Threde GmbH from Munich, the companies that built the
observation device on behalf of the DLR. Besides the turbine vibrations
of the aircraft, turbulences are mainly what shake up the telescope.
For this reason, it is stored inside an air cushion. To ensure that the
object of interest always remains in focus, the mirror substrate is
guided precisely by an automatic device.
Many more tests and installations still lie ahead, before the flying
eye on the sky can take off from its base airport, NASA Dryden Flight
Research Center at Edwards Air Force Base, near Los Angeles
(California/U.S.A.), to embark on its first scientific missions. Up to
15 experts from Germany will be accompanying the experiments. At a
working altitude of over 12,000 meters, they'll be opening an
approximately four by six meter bulkhead door at the tail of the plane
to observe space for several hours on three or four evenings each week.
More flexible research into new phenomena
SOFIA offers even more invaluable advantages. Unlike observation
satellites, this aircraft is not restricted to specific orbits. It can
fly to any large airport on earth. While there, new components can be
installed, instruments can be replaced or sensors can be added in order
to study temporary phenomena that are only visible from certain
locations, solar eclipses or partially covered stars, for example. With
the help of the flying observatory, scientists are hoping to capture
light with wavelengths of between 0.3 and 1,600 micrometers, especially
invisible heat radiation. This makes up a considerable share of the
radiant power of our universe. Some cosmic structures in this spectral
region, for instance, shine some thousand times brighter than optical
structures. This often remains hidden to grounded telescopes, because
this part of the spectrum is usually swallowed up by clouds and water
vapor. This is also why it hasn't been researched more thoroughly. But,
this should change with SOFIA, because it leaves around 99 percent of
the atmospheric humidity behind it. Because the infrared radiation can
even penetrate through interstellar clouds of dust, SOFIA offers views
of previously undiscovered interstellar structures, including galaxies,
groups of stars or the birthplaces of young stars. "This data will
broaden our conception of the composition of the interstellar medium
and the processes that lead to the creation of stars inside our
cosmos," promises Prof. Jürgen Stutzki from the University of Cologne
(Germany) and currently speaker for the SOFIA researchers. Everyone is
optimistic that SOFIA will be a complete success. Initial tests give
cause for optimism. Furthermore, analyses have shown that the flying
observatory achieves approximately ten times the sensitivity and three
times higher resolution than its predecessor, the Kuiper Airborne
Observatory that enabled the rings around the planet Uranus to be
discovered.
However, before SOFIA was able to take off for the skies for the good of
science, yet another symbolic act had to take place. Erik Lindbergh, a
grandson of the legendary aviation pioneer Charles Lindbergh, who
became the first person to ever fly over the Atlantic in 1927,
christened the research aircraft »Clipper Lindbergh«. This is actually
the same name that Lindbergh's widow, Anne Morrow Lindbergh, had given
the aircraft several years earlier, before it had been reconstructed.
All those involved consider this a good omen.
