NASA's Hubble Space Telescope entered a new era of scienceoperations this week, when engineers shut down one of the threeoperational gyroscopes aboard the observatory. The two-gyro mode isexpected to preserve the operating life of the third gyro and extendHubble's science observations through mid-2008, an eight-monthextension.
This conclusion followed detailed analysis by engineers andscientists at NASA's Goddard Space Flight Center, Greenbelt, Md., andthe Space Telescope Science Institute (STScI) in Baltimore. Thoroughtesting of the two-gyro mode was completed prior to implementation.
The gyros are an integral part Hubble's complex pointing controlsystem. The system maintains precise pointing of the telescope duringscience observations. The system was originally designed to operate onthree gyros, with another three in reserve. Two of the six are nolonger functional.
"Hubble science on two gyros will be indistinguishable from thesuperb science we have become accustomed to over the years," saidsenior Hubble scientist David Leckrone at Goddard.
Gyros are the heart, though not the sole component, of Hubble'spointing control system. When only two gyros are available, theobservatory experiences an "unsensed" direction. Using Hubble's FineGuidance Sensors, engineers were able to "fill in" the missing datanormally generated by the third gyro.
Hubble also needs to know its location as it completes oneobservation and slews across the sky to acquire its next target. Thisinformation, previously supplied by the observatory's three gyros, isprovided by onboard magnetometers and Fixed Head Star Trackers.
Many Hubble astronomers were consulted and were part of the overalldecision process about two-gyro science operations. Switching off onegyro can preserve it for future use and extended two-gyro operationaltime for Hubble.
NASA has stated a Space Shuttle servicing mission to Hubble will beconsidered after two successful return-to-flight missions. Theservicing mission would include installing new gyros, batteries, andscience instruments to provide several more years of observations.
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