Fwd = More Falling Satellites On The Way
- Forwarded by: fwestra@... (Frits Westra)
Original Date: Thu, 28 Feb 2002 09:10:44 -0800
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More Falling Satellites On The Way
By Leonard David
Senior Space Writer
posted: 05:20 pm ET
27 February 2002
NASA's has begun to study what on Earth to do with the Upper
Atmosphere Research Satellite (UARS).
This heavy weight spacecraft is due to de-orbit on its own in years to
come, due to natural forces. However there's a problem: UARS was not
designed for a controlled re-entry. That increases the chance it might
not safely crash into remote ocean waters. Due to its size, prospects
are high that leftover chunks of the spacecraft could reach Earth.
NASA is studying whether plucking the craft from orbit via the shuttle
is an option, albeit an expensive choice. Alternatively, the satellite
may be allowed to augur in naturally.
Right now, UARS remains hard at work delving into the workings of
Earth's atmosphere. It was deployed from space shuttle Discovery in
September 1991. UARS, among its duties, is helping develop techniques
for early detection of harmful changes in the ozone layer.
UARS had a design life of 18 months. But after a decade of service the
spacecraft continues to collect Earth science data. The craft weighs
some 13,000 pounds (5,909 kilograms), with eight of its ten
instruments still functioning.
Not to worry...for now
A study was done last month by the NASA Johnson Space Center's (JSC)
orbital debris office. They assessed the probability of human casualty
resulting from an uncontrolled reentry of UARS.
However, don't worry, at least for now.
UARS isn't due to take a tumble from above for another decade,
according to current estimates.
David Steitz, a spokesman for the Earth Science Enterprise at NASA
Headquarters in Washington, D.C., told SPACE.com that the UARS mission
is to continue to operate through the end of September.
UARS is on tap to gather information that might one day complement
data from the European Space Agency's ENVISAT, due for liftoff on an
Ariane 5 booster this Thursday, Steitz said.
"There is no definitive decommissioning date for UARS," Steitz said.
"NASA will conduct periodic assessments to evaluate the cost
expenditures of UARS versus the return of science and our science
needs. The next assessment of the mission will most likely occur in
late spring, looking toward next year," he said.
"UARS was designed in the 1980s, a time when the agency created
'expendable' missions without the same level of attention to reentry
concerns that we have today. UARS was not designed for a controlled
reentry," Steitz said.
No decision has been made on how UARS will come home - on its own, or
tucked in within a shuttle's cargo bay, Steitz said. "We have ample
time to thoughtfully look at all options, and are still considering
all options, with safety as NASA's first priority," he said.
A non-compliant newcomer
While decisions are still forthcoming on what to do with any incoming
UARS, another satellite has also gained the attention of orbital
A team led by William Rochelle of Lockheed Martin's Advanced Systems
Group in Houston, Texas, reports that NASA's soon-to-be-launched Aura
spacecraft has been found to be "non-compliant" with a NASA safety
standard on reentering satellites.
Aura is part of NASA's Earth Observing System (EOS) program. The
spacecraft is slated for launch by a Delta booster in the June-July
2003 time frame, and is under management of the space agency's Goddard
Space Flight Center in Greenbelt, Maryland. Builder of the craft is
TRW Inc. of Redondo Beach, California.
The EOS Aura satellite is based on TRW's EOS Common Spacecraft, and is
a sibling of NASA's EOS Aqua mission. That spacecraft has just arrived
at Vandenberg Air Force Base in California for launch this spring.
Once lobbed into a polar, sun-synchronous orbit, Aura's mission is to
study the Earth's ozone, air quality and climate, and is to operate
for five or more years.
Rochelle reports that Goddard engineers first performed a reentry
analysis of Aura, making use of NASA Johnson Space Center's (JSC)
Debris Assessment Software. That specialized software can assess the
chances of a spacecraft's components surviving a dive through Earth's
atmosphere. Data showed that pieces of Aura would likely reach the
By utilizing a higher fidelity Object Reentry Survival Analysis Tool
(ORSAT) -- developed by specialists at JSC and Lockheed Martin Space
Operations -- it was found that Aura hardware would, indeed, survive a
fiery fall from space.
Survive the dive
The ORSAT assessment found that Aura would break-up on reentry, with
most of the spacecraft consumed by heat during the plunge. However,
due to spacecraft mass, size and materials used, an "increased
possibility" exists that pieces of the over two-and-a-half ton (2,400
kilograms) satellite could survive and pose a safety risk to people on
Several Aura components were found likely to endure the hellish plunge
through thin to thick atmosphere. Among them: A titanium propulsion
module, four steel reaction wheel assemblies; scan mirror assemblies
in one Aura instrument, as well as a beryllium gimbal that's part of
the spacecraft's Tropospheric Emission Spectrometer.
Rochelle and other reentry debris experts point out that titanium,
steel, and beryllium tend to have higher survival tendencies. That's
due to the high temperatures needed to melt those material types.
Using ORSAT, a simulated Aura reentry found the debris footprint to be
some nearly 175 miles (280 kilometers) in length.
For the last several years, NASA has dealt with several deorbiting
The Compton Gamma Ray Observatory was finessed from orbit in 2000
using a series of delicate maneuvers. That craft safely splashed down
in the Pacific Ocean.
Late last month, NASA's Extreme Ultraviolet Explorer (EUVE) spacecraft
returned to Earth on its own. Pieces of that satellite are thought to
have landed somewhere in Egypt. There were no reports of debris being
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