Friday October 10, 2008, 5:20 am
The Hubble Space Telescope's handlers are weighing a plan to turn on a never-used backup system to restore communications as early as next week. If it works, the world's favorite orbiting observatory could be back in business just a couple of days later. If it doesn't, Hubble could conceivably be worse off than it was before.

The space telescope has been out of commission since Sept. 27, when its command and data-handling system abruptly failed. That forced a postponement of NASA's final Hubble servicing mission, which was due to begin this week with the launch of the shuttle Atlantis. The launch has been put off until next year - to give mission planners time to figure out how to make a fix, and to give Atlantis' crew time to practice the operation.

In the meantime, engineers have a devised a plan to switch Hubble's data-handling functions from the primary system, known as Side A, to the Side B backup system. Side B hasn't been put to the test since Hubble went into orbit in 1990.

"The transition to Side B operations is complex," Hubble's managers explained in a mission update released after the breakdown. "It requires that five other modules used in managing data also be switched to their B-side systems."

All the reconfigurations would be made remotely, by beaming commands to Hubble from the ground.

Sources familiar with the plans for the switchover note that there's some risk that the Side B systems won't work. There's even a chance that if the A-to-B switch doesn't work, Hubble wouldn't be able to switch back from B to A. That scenario would complicate plans for the eventual repair mission, and thus provides an argument for leaving things alone until Atlantis arrives.

A spare data-handling unit is being tested at NASA's Goddard Space Flight Center in Maryland, where the Hubble operations team is based. Engineers are also analyzing diagnostic data, according to NASASpaceflight.com, an independent Web site that closely follows the space program.

Hubble's managers reviewed the plans for the A-to-B switch today during a round of meetings at Goddard. More meetings are planned on Friday, and NASA Headquarters would review the recommendations on Tuesday, after the federal Columbus Day holiday.

If NASA's top officials give the go-ahead, the switchover could take place as early as Wednesday. Science operations could resume a couple of days after the switch has been made.

"If Side B goes up, and it's successful, we're looking forward to resuming science observations and coming up with clever programs to fill the time," said Ray Villard, a spokesman for the Baltimore-based Space Telescope Science Institute.

He said the first of Hubble's instruments to be brought back up would be the Wide Field and Planetary Camera 2, or WFPC2. He said reviving Hubble's other working camera, the Near Infrared Camera and Multi-Object Spectrometer, or NICMOS, would be "trickier" because of the camera system's cryogenics. Hubble's Fine Guidance Sensors could conceivably be used for science as well.

Hubble's other two science instruments, the Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph, are currently out of commission and have been slated for repair during Atlantis' visit. Two more instruments, the Wide Field Camera 3 and the Cosmic Origins Spectrograph, are ready for installation.

NASA was already planning to have Atlantis' astronauts do all those upgrades, and change out Hubble's worn-out batteries and gyroscopes as well. Now more complications lie ahead. Will Hubble's handlers go through with the temporary switchover? How will they adjust the spacewalk schedule and the cargo manifest to accommodate the definitive fix for the data-handling system? Stay tuned for next week's episode of "Hubble's Troubles."