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Veteran Landsat 5 satellite on the brink of failure
BY STEPHEN CLARK
SPACEFLIGHT NOW

Posted: November 18, 2011


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An aging Landsat observation satellite could be nearing its end due to a faulty electronic component essential for downloading surface images back to Earth, the U.S. Geological Survey announced Friday.


Artist's concept of Landsat 5. Credit: USGS
 
After several close calls with other components, Landsat 5 is showing signs of an "impending failure" after more than 27 years in space. USGS engineers have suspended image acquisitions using the satellite for at least 90 days, the agency said in a statement.

Over the last several months, satellite controllers monitored fluctuating performance of an amplifier for transmitting images from the spacecraft to ground stations. The amplifier's performance declined more in the last 10 days, according to the USGS.

"Numerous engineering and technical adjustments have been made to Landsat 5 in the past several days to sustain at least a limited imaging capability, but performance has continued to decline," the USGS statement said. "Instead of continuing to operate until the amplifier fails completely, which could bring the mission to an end, USGS engineers have suspended imaging activities for an initial period of 90 days in order to explore every possible option for restoring satellite-to-ground image transmissions."

Launched in March 1984, Landsat 5 has outlived its three-year design life nine times. Landsat 5 collected imagery in the aftermath of the Chernobyl nuclear reactor accident and the Sept. 11 terrorist attacks, plus countless other natural disasters.

"This anticipated decline of Landsat 5 provides confirmation of the importance of the timely launch of the next Landsat mission and the need for an operational and reliable National Land Imaging System," said Anne Castle, assistant secretary for water and science at the U.S. Department of the Interior. "The USGS is committed to maintaining the unique long term imaging database that the Landsat program provides."

The launch of the Landsat Data Continuity Mission, which will become Landsat 8, is scheduled for Jan. 15, 2013.

Landsat 5 was providing better data than the younger Landsat 7 satellite, which launched in 1999.

Part of Landsat 7's imaging instrument stopped working in 2003, significantly reducing the quality of data from the satellite.

The faulty part is called the scan line corrector, a mirror-like assembly that compensates for the "zigzag" motion of the image scans by the Enhanced Thermal Mapper Plus instrument.

Due to the glitch, each scene is missing about 22 percent of data, leaving gaps that give make some researchers hesitant to use Landsat 7 imagery. Scientists studying crops, forests, the water cycle and other disciplines say they preferred Landsat 5's data for their work.

An interruption in the Landsat program could harm research into climate change, ice fields, the carbon cycle and operational interests in agriculture, land use and resource management.

The Landsat program has kept a constant vigil over Earth since the launch of Landsat 1 in 1972. The constellation's 39-year legacy provides a robust archive of data at the fingertips of scientists.

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