NASA shut down one of the Hubble Space Telescope鈥檚 pointing gyroscopes this week in an effort to keep the observatory alive for an extra eight months or so. The scaled-down operating mode may extend the telescope鈥檚 lifetime until mid-2008 but will have some impact on the telescope鈥檚 ability to schedule observations.
Hubble was originally designed to use three of its six gyroscopes to point and stabilise itself in space. But the gyros regularly fail, and astronauts have already replaced them twice. Currently, two are broken 鈥� apparently because clumps of lubricant or small particles are preventing their bearings from turning smoothly.
So the 15-year-old observatory is using just three gyros, with another in 鈥渟tandby鈥� mode in case of another failure. The current configuration of gyros is expected to keep the telescope going until about 2007.
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Image quality
But NASA engineers believe the telescope will survive until mid-2008 now that they have put another gyro into standby mode. In this scenario, the telescope will operate on two gyros and if one fails, NASA can slot in one of the two standbys, repeating the process if a second gyro fails.
The change is not expected to directly affect the quality of Hubble鈥檚 celebrated images. Tests of the mode, in which onboard computers only used data from two gyros, showed the resulting images were nearly identical to those taken with three gyros.
鈥淗ubble science on two gyros will be indistinguishable from the superb science we have become accustomed to over the years,鈥� says senior Hubble scientist David Leckrone of NASA鈥檚 Goddard Space Flight Center in Greenbelt, Maryland, US.
Reduced flexibility
But the quality of astronomy research carried out by Hubble could be impacted. In lieu of a third gyroscope, Hubble must use 鈥渟tar-tracking鈥� cameras to orient itself. These trackers look out in a different direction from the telescope tube, so Hubble cannot make observations when Earth gets in the trackers鈥� field of view.
This will probably halve the number of days the telescope can observe any given object, which will significantly reduce the flexibility for scheduling observations.
The stay of execution is crucial, since NASA will not commit to sending astronauts to service the telescope until after the next shuttle safely returns to flight. The shuttles are currently grounded until at least March 2006 and may be delayed further because Hurricane Katrina has damaged the plant that makes the shuttle鈥檚 external tanks in Louisiana, US.
