Two months shy of its 22ndbirthday, the Landsat 5 Earth observatory has a new lease on life aftercontrollers dodged a potentially fatal bullet involving a crucial mechanism incharge of pivoting the craft's solar array that began to show problems inNovember.
The solar array drivesystem is responsible for ensuring the satellite's power-producing solar panelscan correctly point toward the Sun throughout each 99-minute circuit around theEarth. Electricity is then stored in on-board batteries for use during thenighttime portion of the orbit.
Without this importantdevice, imaging operations are not possible due to inadequate power reserves.Landsat 5 had already encountered a difficulty with the solar array drivesystem last January when the primary mechanism failed after functioningnormally for almost 21 years. Engineers studied that issue and declared it atotal loss, leaving the venerable spacecraft reliant upon a backup driver.
Similar behavior was notedin the secondary system on November 26, and movement of the drive became toosporadic to provide the needed electrical power to sufficiently charge thebatteries, the United States Geological Survey said in a statement late lastyear. Normal operations were immediately halted to allow controllers to studythe problem.
Engineers conducted amonth-long investigation before finalizing a testing plan that was carried outthrough the first few weeks of January. The tests resulted in a set of newoperating practices that make it possible for Landsat 5 to return to its roleas a key environmental observation satellite used by scientists and otherofficials around the world.
The first new images oftargets inside the continental United States were captured a week ago, andinternational observations are set to resume within the next few weeks.
"This is good news forthe global science and operational communities," said the USGS Land RemoteSensing Program Coordinator, Jay Feuquay. "The Landsat program has awell-established record of over 30 years of Earth observations. The latestdevelopments allow the Landsat user community to continue to rely on Landsatimagery. I am optimistic about the 'fix' applied to the solar array problem andthe future operations of Landsat 5."
Landsat 5 was launched intopolar orbit on March 1, 1984, from California's Vandenberg Air Force Base atopa Delta rocket to begin what was then anticipated to be a three-year mission togather images of locales across the globe. The spaceborne survey platform isjust one of two remaining members of the original Landsat fleet - joining themore recent addition of Landsat 7 in a combined mission to continue the Landsatlegacy in producing tools for scientists to better monitor Earth's surfacechanges on scales ranging from weeks to decades. Operating in tandem, the duocan offer full global coverage on an eight-day cycle.
The long-lived observatoryhas taken over 620,000 images in its almost 22 years in orbit, witnessing from435 miles high a number of major world events including the Chernobyl disaster,two wars in Iraq, the 2004 tsunami, and Hurricane Katrina.
Landsat 7 has beensuffering from the loss of an imaging instrument component known as the scanline corrector since mid-2003. The SLC compensates for the forward motion ofthe craft as it speeds along at five miles per second. Officials opted to offerreduced quality images without the use of the SLC by late 2003, and theseproducts are still on the market today.
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