WASHINGTON -- The promotional video shows a multi-jointed titanium handyman untwisting knobs and disconnecting an electrical cable with slow-motion aplomb, displaying fine motor skills that the voice-over assures will enable it to install "new batteries, gyroscopes and scientific instruments" aboard the aging Hubble Space Telescope.

But the video is only a teaser. In April, when NASA's Goddard Space Flight Center in Greenbelt, Md., showed the whole sequence to headquarters VIPs, what had first seemed an elusive dream -- a robotic mission to service Hubble and extend its life by five years or more -- suddenly became real.

"I remember coming to look at this stuff and asking, 'Is that an [animation]?' And somebody said, 'No, it's really happening,'" recalled Edward Weiler, who was NASA's associate administrator for space science at the time and is now Goddard's director. "I didn't think robots could do this kind of stuff."

It is by no means a sure thing. Yet largely because of the Canadian robot named "Dextre," NASA has gone in less than a year from virtually writing off the Hubble to embracing a mission that will cost between $1 billion and $1.6 billion and approach in complexity the hardest jobs the agency has ever undertaken.

To do it, the United States must develop its first-ever robotic docking vehicle, fill a bag with tools that, in many cases, have not been invented, and use the robot repairman to unscrew j-hooks, open and shut doors and "drawers," disconnect and attach electric connectors, and rig jumper cables.

By the end of 2007, NASA hopes to put into orbit its Hubble Robotic Vehicle of four components: a de-orbit module designed to dock with Hubble; a grappling arm to seize the telescope during docking and serve as a repair platform; an ejection module to carry spare parts and tools; and Dextre.

The jobs, in descending order of importance, are to change Hubble's batteries; install new gyroscopes; swap an old camera for a new, more sophisticated one; install a new spectrograph; and, if possible, replace a telescope pointing device and repair another spectrograph.

"There's nothing easy about it. It's all firsts," said Goddard's Preston Burch, Hubble's program manager. "And some of the things we're thinking about make people nervous."

In the past, shuttle astronauts had the job of servicing Hubble, missions that required a few days of spacewalks lasting six hours each. Dextre "can work 24-7," Weiler said -- a fortunate feature, because robots are not as supple as humans. "Watching it is like watching grass grow," Weiler said.

Burch hopes to complete the mission in a month. Some of it will be done by the robot working on its own, but most will be handled by ground controllers manipulating the robot's two arms -- like playing a video game.

Dextre, so nicknamed by the Canadian Space Agency, was developed by MD Robotics, of Brampton, Ontario, as the Special Purpose Dextrous Manipulator, a robotic repairman destined for eventual duty on the international space station.

Dextre has a central "torso" with two 10-foot arms that can pivot, turn, reach and grab in seven different ways. In repose, it is a 2,220-pound, Rube Goldberg-style titanium stick figure, but in action it can readily choose a mix of intricate movements to execute the commands of its operator.

Dextre's future changed dramatically in January, after NASA Administrator Sean O'Keefe canceled a scheduled shuttle servicing mission to Hubble, citing safety concerns after last year's Columbia tragedy.

Public outrage greeted this decision, which essentially sentenced Hubble to a watery grave once its batteries give out, but O'Keefe left open the possibility of robotic repair, and NASA sent out a bulletin asking for proposals.

MD Robotics responded to the bulletin, and Goddard asked to see Dextre perform. "We were able to demonstrate a lot that astronauts had done," said Dan King, MD Robotics' director for orbital robotics. "We opened doors, gained access, changed an existing connector, that kind of thing."

After Goddard and MD Robotics engineers dazzled the NASA brass in last April's demonstration, excitement started to build, climaxing in August, when O'Keefe traveled to Goddard to tell the Hubble team to get to work on a robotic mission to fly by the end of 2007.

Late last month, NASA awarded MD Robotics a $144 million preliminary contract to provide Dextre and the grappling arm, and gave a $330.6 million contract to Lockheed Martin for the de-orbit module. Goddard will build the ejection module and assemble the package, which will weigh about 24,000 pounds, fully fueled.

NASA set 2007 as the deadline, at first suggesting that Hubble's batteries would give out by then and cause the telescope to shut down within hours. But Weiler said a second set of test batteries on the ground show that Hubble's power should last until 2009. Still, engineers are sticking with an early launch in case the schedule slips.