It was the latest twist in the long-running drama surrounding the 18-year-old space telescope - one that initially took only fuzzy photos, then when fixed, provided dazzling and scientifically significant pictures of space, including a new one NASA showed Thursday.
A repair and upgrade mission to the telescope was nixed a couple of years ago as too risky for the astronauts. But enthusiasm and improved safety measures convinced NASA's current chief, Michael Griffin, to go forward with it.
That flight was supposed to happen in mid-October. But the science computer on the telescope unexpectedly shut down, so everything was put on hold. NASA was finally able to get a backup computer system to work in recent days.
But officials can't count on that backup working indefinitely, so they want astronauts to install an additional system part. That part, in storage since 1991, revealed a "significant" problem during testing, said Hubble program manager Preston Burch. It won't be ready to fly for at least six months, he said.
"I don't see this as a huge insurmountable deal," he added.
But if engineers don't get the spare box working properly, NASA will have to face a decision on whether to do the upgrade mission at all, said Jon Morse, NASA's astrophysics chief. That is because of the potential futility of upgrading an observatory that could fail at any moment.
That's not an issue right now, said NASA spokesman Ed Campion: "We're a long way from declaring anything absolutely failed."
The delay also may hinder another bigger NASA program, its new moon rocket that NASA hopes to launch by 2015. The space agency needs to spend several years reconfiguring a Kennedy Space Center launch pad for the new moon rocket testing. But that's the pad the Hubble repair mission will launch from.
For the time being, the $10 billion telescope is as good as it was before it shut down a few weeks ago, according to the Hubble Space Telescope Science Institute in Baltimore.
To prove it, NASA released a glimmering new Hubble photo showing two ring-shaped galaxies after they collided. Ray Villard, spokesman for the institute, called the image a "weird interaction" of the two galaxies which are 440 million light-years away.