Landsat 5 Satellite Recovers From Latest Glitch

by Stephen Clark

Date: 28 January 2006 Time: 11:58 AM ET

Two months shy of its 22nd birthday, the Landsat 5 Earth observatory has a new lease on life after controllers dodged a potentially fatal bullet involving a crucial mechanism in charge of pivoting the craft's solar array that began to show problems in November.

The solar array drive system is responsible for ensuring the satellite's power-producing solar panels can correctly point toward the Sun throughout each 99-minute circuit around the Earth. Electricity is then stored in on-board batteries for use during the nighttime portion of the orbit.

Without this important device, imaging operations are not possible due to inadequate power reserves. Landsat 5 had already encountered a difficulty with the solar array drive system last January when the primary mechanism failed after functioning normally for almost 21 years. Engineers studied that issue and declared it a total loss, leaving the venerable spacecraft reliant upon a backup driver.

Similar behavior was noted in the secondary system on November 26, and movement of the drive became too sporadic to provide the needed electrical power to sufficiently charge the batteries, the United States Geological Survey said in a statement late last year. Normal operations were immediately halted to allow controllers to study the problem.

Engineers conducted a month-long investigation before finalizing a testing plan that was carried out through the first few weeks of January. The tests resulted in a set of new operating practices that make it possible for Landsat 5 to return to its role as a key environmental observation satellite used by scientists and other officials around the world.

The first new images of targets inside the continental United States were captured a week ago, and international observations are set to resume within the next few weeks.

"This is good news for the global science and operational communities," said the USGS Land Remote Sensing Program Coordinator, Jay Feuquay. "The Landsat program has a well-established record of over 30 years of Earth observations. The latest developments allow the Landsat user community to continue to rely on Landsat imagery. I am optimistic about the 'fix' applied to the solar array problem and the future operations of Landsat 5."

Landsat 5 was launched into polar orbit on March 1, 1984, from California's Vandenberg Air Force Base atop a Delta rocket to begin what was then anticipated to be a three-year mission to gather images of locales across the globe. The spaceborne survey platform is just one of two remaining members of the original Landsat fleet - joining the more recent addition of Landsat 7 in a combined mission to continue the Landsat legacy in producing tools for scientists to better monitor Earth's surface changes on scales ranging from weeks to decades. Operating in tandem, the duo can offer full global coverage on an eight-day cycle.

The long-lived observatory has taken over 620,000 images in its almost 22 years in orbit, witnessing from 435 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 been suffering from the loss of an imaging instrument component known as the scan line corrector since mid-2003. The SLC compensates for the forward motion of the craft as it speeds along at five miles per second. Officials opted to offer reduced quality images without the use of the SLC by late 2003, and these products are still on the market today.