The space shuttle Atlantis is due to blast off on Monday, May 11, on its way to a rendezvous in orbit with the Hubble Space Telescope. It will be the fifth and final space repair flight to the orbiting observatory.

Once in orbit, the astronauts will maneuver the telescope into the shuttle's cargo bay, where they can do what's needed to keep Hubble in good shape until its replacement is launched, five years from now.

The telescope will be getting new science instruments, batteries and gyroscopes, says astronaut Mike Massimino.

"We're going to put in a new wide-field camera, which is going to increase the telescope's ability to see into the universe by a factor of 10, so we can see a lot of cool stuff if we do our job right and this thing works. So we're excited about the wide-field camera and also the cosmic origins spectrograph, which is another big scientific instrument we're putting in. So those things are going to increase the science capability of the telescope."

Massimino, who will be on two of the five space walks, was on one of the four previous Hubble repair flights. His crewmate, John Grunsfeld, was on three of them.

"The Hubble has been in orbit for 18 years. It's a remarkable period of time for any spacecraft to be operating at the level Hubble has, and in an environment that's pretty nasty, and that takes its toll on the telescope."

Grunsfeld's academic background is in physics and astronomy. He says it's important to keep Hubble working as long as possible because of the contributions the space telescope has made to science.

"It has produced all of the science that we expected it would - the discovery that black holes really do exist, massive black holes millions of times the mass of our sun. It's measured the age of the universe. It's answered just so many of those fundamental questions that people have been asking about the cosmos since people have been able to ask questions," Grunsfeld said.

After the shuttle program's second fatal accident in 2003, NASA canceled the planned repair mission to Hubble. Space agency officials considered the flight too dangerous. If there were any problem with the shuttle, they said, the astronauts would be stranded, unable to seek the safe-harbor refuge of the space station, which flies in a different orbit.

But astronomers and other supporters of the space telescope urged the decision be reversed. Which it was, but only after NASA added some new safety measures. Crew commander Scott Altman explains what happens if they get into trouble.

"So we will shelter in place on our [shuttle] orbiter," said crew commander Scott Altman, "power down to extend the life, the oxygen, and we can go up to roughly 25 days waiting for somebody to come up to us."

Meanwhile, the space shuttle Endeavour will be standing by in case a rescue mission is needed.

"We have done a great deal of planning and work on the launch-on-need," says NASA official LeRoy Cain, "and so Endeavour is ready to go on Pad B if we should need it for launch-on-need."

With only a handful of shuttle flights left on the program's manifest, NASA has begun laying off workers. Nearly three decades after the first shuttle flight in 1981, the three remaining orbiters are set to be grounded next year.