Hubble Space Telescope put into hibernation after critical system failure

The Hubble Space Telescope

November 15, 1999
Web posted at: 8:49 p.m. EST (0149 GMT)

GREENBELT, Maryland (CNN) -- With three weeks to go before it is due for an urgent in-orbit service call, the Hubble Space Telescope suffered a critical system failure -- leaving the $6 billion instrument scientifically useless.

Engineers at the Goddard Space Flight Center on Saturday morning put the Hubble into so-called "safe mode" after a gyroscope failed. Its failure left only two of its six gyroscopes operative -- and the space telescope needs a minimum of three gyros to aim precisely.

Three other gyros already had failed, prompting enough concern at NASA to move up a shuttle mission to service and repair the telescope.

But a series of problems with the space-shuttle fleet delayed the launch of that mission. A laborious series of inspections and repairs to the wiring inside the shuttle Discovery -- as well as an engine swap after a piece of a drill bit was discovered in the cooling system -- have forced shuttle managers to reschedule the launch for December 6.

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The flight plan calls for two pairs of astronauts to conduct a series of four daring spacewalks to repair and improve several components on the Space Telescope which was launched in 1990. At the top of their work order: replacement of all six gyroscopes.

Assuming the shuttle arrives on schedule, Hubble will have been in its hibernation mode for more than three weeks. While the telescope has been safe mode twice before, it has never slept for that long, which has created some nervousness.

"We have never looked at the possibility of being off-line for three weeks," said Space Telescope Science Institute spokesman Ray Villard.

Villard says about 100 astronomical observations will be lost while the Hubble is shut down. Most can be scheduled later, but a few -- like some planned observations of an exploding star called a supernova, and a joint venture with the NASA probe Galileo -- cannot be replicated.

Hubble costs U.S. taxpayers about $20 million per month to remain in operation, regardless of whether it is generating images.

In safe mode, the Hubble's lens cap (aperture door) is shut and a sun-sensor and star-tracker are employed to keep the telescope's solar arrays pointed toward the sun. Those devices provide enough guidance to keep Hubble properly oriented but are not sensitive enough to allow the instrument to take pictures. When the Hubble is in darkness, it reverts to a "controlled drift."

A cluster of much less accurate, back-up gyroscopes called the "retrieval mode gyro assembly" will be used to aim the Hubble properly so that the shuttle can rendezvous and grab the telescope with its 50-foot robotic arm. The shuttle Discovery crew, led by Cmdr. Curt Brown, have used simulators in Houston to train for precisely that scenario.

That package of backup gyros has never been used. If it fails, "the crew can grapple the Hubble if it is in free-drift," says NASA spokesman Rob Navias. "There is a certain rate of drift up to which they could grapple."

The Hubble was designed to be serviced and repaired by shuttle crews. This will be the third such repair mission. Two more are planned before the telescope is slated to be retired -- and probably carried back to earth -- in about 10 years.