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Fwd = More Falling Satellites On The Way

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  • Frits Westra
    Forwarded by: fwestra@hetnet.nl (Frits Westra) URL: http://www.space.com/news/uars_plans_020227.html Original Date: Thu, 28 Feb 2002
    Message 1 of 1 , Feb 28, 2002
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      Forwarded by: fwestra@... (Frits Westra)
      URL: http://www.space.com/news/uars_plans_020227.html
      Original Date: Thu, 28 Feb 2002 09:10:44 -0800

      ========================== Forwarded message begins ======================


      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
      debris experts.


      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
      surface.


      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
      the ground.


      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
      scientific satellites.


      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
      recovered.
      _________________________________________________________________

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