| From: [email protected] (Steve Willner)
Newsgroups: sci.space
Subject: IUE (NASA Press Release)
Date: 18 Apr 88 19:33:32 GMT
Organization: Harvard-Smithsonian Ctr. for Astrophysics
Here's a NASA press release from back in January. I'm posting it
a bit late, but it's still relevant. My own comments are in {braces}.
Charles Redmond
Headquarters, Washington, D.C. January 22, 1988
(Phone:202/453-1549)
Randee Exler
Goddard Space Flight Center, Greenbelt ,Md.
(Phone:301/286-7277)
INTERNATIONAL ULTRAVIOLET EXPLORER MARKS DECADE OF RESEARCH
When NASA launched a space-based telescope called the
International Ultraviolet Explorer (IUE), it was expected to last only
3 years, perhaps 5 at the most.
On Jan. 26, the IUE will complete a decade of continuous operation
during which it was instrumental in some of the most important
advances in modern astronomy.
The IUE is credited with the discovery of galactic halos (hot gas
which surrounds our galaxy {They must mean other galaxies; I don't
think IUE has seen the halo of our Galaxy.}), monitoring volcanic
activities on Io (a moon of Jupiter), beaming the first images ever
recorded of Halley's comet from space and monitoring, since Feb. 24,
1987, the intense emissions of ultraviolet radiation from Supernova
1987A, an exploding star approximately 163,000 light years from Earth.
Dr. Yoji Kondo, IUE project scientist at NASA's Goddard Space
Flight Center (GSFC), Greenbelt, Md., maintains, "The IUE is one of
the most productive telescopes on or off the planet.
"One measure of the productivity of a scientific instrument is the
number of papers published in referred journals about work using that
instrument," he said. "As the IUE completed its 10th year in orbit,
more than 1,400 articles, based on IUE observations, have been
published in refereed journals. This far exceeds the number of
articles based on data from other telescopes in similar journals
during the same time period. The papers are based on research of
astronomers from around the world who conduct their studies in
real-time on both sides of the Atlantic." {For comparison, the
leading US journal publishes about 1000 papers per year. Of course,
many IUE papers contain data from other telescopes too.}
The IUE was placed in a geosynchronous orbit over the Atlantic
Ocean, enabling operations around the clock. The satellite telescope
is controlled from the science operations center at GSFC for 16 hours
and in Spain, with the Villafranca Ground Station near Madrid, for 8
hours. IUE staff astronomers at GSFC, under contract by the Computer
Sciences Corporation, Beltsville, Md., assist visiting astronomers
with their work. The Bendix Field Engineering Corporation performs
spacecraft maintenance operations 24 hours-a-day from GSFC.
The IUE is a joint effort of NASA, the European Space Agency (ESA)
and the British Science and Engineering Research Council (SERC).
Goddard scientists, engineers and technicians designed, integrated and
tested the IUE. An ESA team built the solar array and the ground
facilities near Madrid. SERC, in collaboration with University
College, London, provided four TV camera detectors for transforming
the spectral displays into video signals.
These organizations select observers and programs through annual
proposal competitions. In January 1987, the total number of U.S.
guest proposals for the 10th year of operation reached 320, the
highest number for any year. Over the years, the total number of IUE
guest observers at GSFC came to more than 800 different astronomers,
while the number for the control center in Spain totaled more than 750.
"These figures indicate that a very substantial number of the
world's astronomers have used the IUE for their work at one time or
another," said Kondo.
Goddard engineers, astronomers and analysts encountered a serious
problem with IUE when one of its remaining three gyros failed and the
spacecraft lost its pointing capability in 1985. Of the IUE's
original six gyros (three had previously failed in 1979, 1982, and
1983), the 1985 gyro failure left only two working gyros.
Spacecraft traditionally need a minimum of three gyros to
determine the spacecraft roll, pitch and yaw reference to point at
targets and maintain stabilization during observations. The problem
of maintaining three-axis stabilization with only two gyros is
considered nearly impossible to achieve.
A plan was devised and implemented by Goddard's guidance and
control team, led by GSFC engineer Henry Hoffman, that asubstituted
one axis of the IUE's sun sensor for the lost gyro, thus maintaining
three-axis control on only two gyros. Not only did using the sun
sensor stabilize the ailing spacecraft, but pointing accuracies and
stability remained virtually unchanged.
"The IUE has an entirely new set of control laws which bear no
resemblance to what was there before," explained Hoffman.
"We have a one-gyro system sitting in our hip pocket," he added.
This software has been fully checked out on the ground and will be
uplinked to the IUE if and when one of the remaining two gyros fails.
The one gyro system uses the second axis of the sun sensor in lieu of
one of the remaining two gyros.
"We have a concept and plans for developing a zero-gyro system,"
Hoffman claimed. "Two reference axes will be derived from the sun
sensor, and the third reference by carefully managing the speed of the
spacecraft's reaction wheels." The zero-gyro concept is being studied
and appears feasible at this time.
There are many ground-based telescopes much larger and more
powerful than the IUE but being space-borne vastly improves the
acquired images due to the absence of clouds or atmosphere that
obscure vision. {"Improves" is a bit of an understatement, since the
atmosphere is completely opaque at the ultraviolet wavelengths where
IUE works.}
Steve Willner Phone 617-495-7123 Bitnet: willner@cfa
60 Garden St. FTS: 830-7123 UUCP: willner@cfa
Cambridge, MA 02138 USA Internet: [email protected]
|
| Paula Cleggett-Haleim
Headquarters, Washington, D.C. September 22,
1993
Michael Finneran
Goddard Space Flight Center, Greenbelt, Md.
RELEASE: 93-164
New software is giving researchers a remarkably improved look at data
from NASA's International Ultraviolet Explorer (IUE), the space
agency's longest-running astronomical satellite in Earth orbit.
Called the New Spectral Imaging Processing System (NEWSIPS), the
software uses algorithms -- mathematical instruction codes -- that
reveal previously hidden information in the IUE data, according to
scientists at NASA's Goddard Space Flight Center, Greenbelt, Md.
"With this new software, we can revisit our old data and find all
sorts of things in there that we never could have seen before," said
Dr. Andrew G. Michalitsianos, Head of the Observatory Section at
Goddard, which built and manages IUE. "Who knows what we'll turn up."
The 15-year-old IUE was originally launched with a 5-year mission goal
but is still functioning today.
The new system subtracts fixed-pattern noise from the IUE data,
Michalitsianos said. Noise is an underlying and unwanted signal that
can mar data quality, much like scratches on a record album, hiss on a
tape or poor reception on a TV. The IUE noise comes from the
ultraviolet detector on the spacecraft.
The software was developed jointly by Goddard and the European Space
Agency's Villefranca Satellite Tracking Station in Spain. Such
software was not available when the spacecraft was launched in January
1978.
Since then, IUE has beamed a prodigious volume of data back to Earth.
Now scientists can review past findings and using the new software,
enhance the quality of the data three to four times, said
Michalitsianos.
Michalitsianos said the new software works particularly well on data
fro m faint objects in the Milky Way Galaxy. As a test of the new
system, he said, researchers reprocessed data gathered by IUE in 1978
on an object in space known as the gravitationally lensed binary
quasar 0957+561.
A quasar is a quasi-stellar object that emits strong radiation, which
ma y become faint if it is very far away. A gravitationally-lensed
binary quasar is a quasar whose light has been bent by a galaxy
positioned between it and the Earth. The intervening galaxy's
gravitational field acts like a lens to curve t he quasar's light
around it. Seen from Earth, the quasar appears as a double image due
to the splitting of its light above and below the object's actual
position.
Using NEWSIPS to reprocess IUE data on the quasar, scientists
discovered previously undetected spectral features that suggest the
presence of an extremely hot x-ray-emitting gas, Michalitsianos said.
Spectral features describe the amount and type of energy emitted from
an object at a specific wavelength in the electromagnetic spectrum.
"This is the first test of NEWSIPS that has borne scientific fruit,"
Michalitsianos said, "and it's an important demonstration of the
capabilities of the software."
The results of the quasar data reprocessing are scheduled to appear in
a paper in the Nov. 10, 1993, issue of "The Astrophysical Journal,"
said Michalitsianos, the lead author. Also contributing were
Demosthenes Kazanas, Yoji Kondo, Michele De La Pena and Stephen Maran
of Goddard; Joy Nichols- Bohlin, Thomas Meylan, Mario Perez and Randy
Thompson of Computer Sciences Corp.; and Fred C. Bruhweiler of the
Catholic University of America in Washington, D.C.
About 100,000 other IUE spectra stored at Goddard's National Space
Science Data Center are being reprocessed with NEWSIPS, Michalitsianos
said. In a few months, he added, reprocessed data will begin to be
released to the scientific community.
"It's very exciting," said Michalitsianos. "This is really exploiting
the full capability of the satellite. You're really realizing the
full investment of the mission."
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