Hubble fixed.

MSNBC

The revival of the Hubble Space Telescope is going "exactly as we hoped," a NASA spokesman said today, and the world's best-known orbiting observatory is expected to be back in business on Friday.

Hubble's science operations went on the blink last month when the main system for handling commands and data going back and forth between the telescope's instruments and the ground failed. Controllers could still send commands up to Hubble and receive diagnostic readings, but the flow of imagery that made the telescope famous was cut off.

The sudden, unexpected snag forced the postponement of the space shuttle Atlantis' final service call, which was due for launch this week.

To revive Hubble, engineers at NASA's Goddard Space Flight Center devised a plan to switch the flow of data from the main system that the 18-year-old telescope had always used, known as Side A, to a never-before-used backup system known as Side B. The space agency's top management gave the go-ahead for the remote-controlled switchover on Tuesday, and engineers went to work on Wednesday.

Engineers checked out Side B for the first time on Wednesday night, NASA spokesman Ed Campion told me today. "All that went exactly as we hoped, so after that, the Advanced Camera for Surveys and the Wide Field Planetary Camera 2 were retrieved out of safe mode to establish that each of them has a good working interface to Side B," he said.

Hubble's reconfigured electronics passed that test as well. "Everything worked the way we hoped it would," Campion said. "Now we're going to send commands to begin internal exposures and calibrations of the science instruments."

The test pictures won't be scientifically significant. They'll merely show things like the illuminated insides of the telescope itself. But they will give scientists at the Space Telescope Science Institute in Baltimore some Side B data to compare with Side A data captured before the glitch.

The Side B data should be available for review by midnight ET tonight, and the before-vs.-after review should be completed sometime Friday morning.

"If all this goes as planned, we pretty much expect that science collection will resume sometime on Friday," Campion said.

Susan Hendrix, a NASA spokeswoman who specializes in following Hubble operations, said the telescope team hasn't yet decided what the first post-switchover scientific target would be. She also declined to speculate on when the first science images would be released. "I don't want to jinx it," she said. "It should be sooner than later."

Like many at NASA, Hendrix said she felt a personal stake in the telescope's ups and downs. "Hubble's been very near and dear to me," she told me. "It's kind of like an adopted child."

Even if Hubble resumes science operations, the child will still have to undergo some follow-up surgery: A spare unit is currently being tested at Goddard, and if that checks out, it will likely be brought up on Atlantis for installation (along with lots of other Hubble goodies) next year. Even when the new unit is in place, Hubble data will continue to flow through the Side B electronics, and Side A would become the backup. That's in line with a common-sense rule for engineers: "If it's no longer broke, don't try fixing it again."