This story was updated at 11:34 a.m. EST.

The decision is in and the Hubble Space Telescope is saved.

NASA announced Tuesday that it will go ahead with one final space shuttle mission to repair and upgrade Hubble after months of debate over the risks of such an endeavor.

"We are going to add a shuttle servicing mission of the Hubble Space Telescope to the shuttle's manifest to be flown before it retires," announced NASA chief Michael Griffinat the agency's Goddard Space Flight Center in Baltimore, Maryland, where Hubble engineers and scientists gave him a standing ovation. "This is a day that I've wanted to get to for the last 18 months."

"Hubble is one of the great observatories," Griffin has said. "It has revealed fundamental things about the universe of which we had no idea."

Griffin said today that the $900 million servicing mission will likely launch aboard NASA's Discovery orbiter between construction flights to complete the International Space Station (ISS), and is expected to feature no less than four--and preferably five--spacewalks to upgrade Hubble's optics and make other repairs.

"We're trying for early May of 2008," Griffin said.

Veteran shuttle flyer Scott Altman will command the mission, with first-time flyer Gregory Johnson servicing as pilots and astronauts Andrew Feustel, Michael Good, John Grunsfeld, Michael Massimino and Megan McArthur servicing as mission specialists. Their mission will launch from NASA's Kennedy Space Center spaceport in Cape Canaveral, Florida, where a second shuttle will stand ready on a second launch pad to serve as a rescue vehicle if needed.

The astronauts will discuss their duties in press conference scheduled for at 2:30 p.m. EST (1930 GMT) today. NASA will also hold an earlier press conference at 12:45 p.m. EST (1745 GMT). [Click here for live NASA TV via SPACE.com's feed.]

Astronomers hope the decision means Hubble could still be in operation by 2013 when NASA's next great observatory--the James Webb Space Telescope--is slated to fly. Hubble's visible and ultraviolet observations will not be duplicated by JWST, which will scan primarily in the infrared wavelengths, researchers said.

"I think it is important to at least make the decision, because that will then tell us [what's happening]," University of Texas astronomer J. Craig Wheeler, president of the American Astronomical Society, told SPACE.com. "It's terribly important to make a decision."

Daunting mission ahead

Hubble-bound shuttle astronauts have a daunting task ahead of them. Their tasks include:

• The installation of Wide Field Camera-3, a new camera to amplify Hubble's vision.
• The replacement of Hubble's batteries, some thermal insulation and a broken guidance sensor.
• Refurbishment of the Hubble's vital attitude controlling gyroscopes used to orient the space telescope. Only two of the six are in operation. Two are held as spares while two others are broken.
• The installation of the Cosmic Origins Spectrograph and unprecedented repair of Hubble's Space Telescope Imaging Spectrograph (STIS), which was never designed to be worked on in space.
• Using the shuttle's engines to boost Hubble into a slightly higher orbit.

The servicing mission will be the fifth shuttle flight to maintain the aging Hubble telescope since its April 1990 launch and NASA's sixth Hubble-dedicated orbiter flight.

"We're essentially going to get a new Hubble," said Sen. Barbara Mikulski, (D-Maryland), who has been a staunch supporter of a final servicing mission to the space telescope, during the announcement at Goddard. "It's a great day for science. It's a great day for discovery."

Ed Weiler, director of NASA's Goddard center, said the next Hubble servicing mission will also include the installation of fixtures designed to connect with a future de-orbit module that would guide the space telescope's controlled disposal plunge through the Earth's atmosphere in the next decade or so.

"We really don't, probably, have to go up there until the 2020 or 2025 timeframe," Weiler said, adding that by then NASA's Orion Crew Exploration Vehicles (CEV) are expected to ferry astronauts back to the Moon. "If the CEV can go to the Moon, it can probably take up a solid rocket motor to Hubble."

Long road to Hubble

NASA initially cancelled the upcoming Hubble servicing flight in 2004, citing the proposed mission as unsafe following the 2003 Columbia accident that killed seven astronauts. But the agency eventually backpedaled after outspoken disapproval from the science community and public, and support by the then-newly installed Griffin.

After first studying the potential to service Hubble robotically, NASA ultimately returned to an astronaut-based servicing mission.

Astronaut safety in orbit topped NASA's list for a potential Hubble servicing mission.

"We are not going to risk a crew in order to do the Hubble mission," Griffin said today.

The tragic 2003 loss of Columbia and its crew stemmed from heat shield damage that went undetected during the orbiter's 16-day mission. NASA now trains more than 100 cameras on orbiters during liftoff, record the flight with onboard cameras, followed by a series of in-orbit heat shield inspections with a robotic arm-mounted boom.

Should serious damage prevent an orbiter's return, most of NASA's remaining astronaut crews can simply take refuge aboard the International Space Station, where they will already be docked there to complete the outpost's construction by NASA's September 2010 shuttle retirement date.

But the Hubble-bound mission will not carry that ISS safe haven plan, prompting NASA's commitment to having a second shuttle ready to fly before staging the servicing flight in the first place.

"We will carry that rescue option in the manifest," Griffin said today. "And that rescue option will consist of a shuttle waiting on the other pad from which we launch the Hubble flight."

Griffin has conceded that devoting a NASA shuttle mission to service Hubble does interfere slightly with the ISS construction flow, but it does not disregard the obligations of NASA to its international ISS partners.

"Obviously, that's a flight that we're doing that's not an assembly mission," Griffin said, adding that Hubble has always been a joint mission between NASA and the European Space Agency. "Hubble itself has had international participation and its contributions to the advancement of knowledge have been international in nature."

But science aside, it has always been the pictures of the universe that have been Hubble's strength, a forte that will apparently continue for quite some time.

"Hubble has probably been the most incredible instrument ever," Livio said. "Not just in doing the science, but bringing that science to the awareness of people all over the globe."

The Hubble story so far:

• NASA Cancels Shuttle Mission to Service Hubble
• Public Bombards Operators to Save Hubble
• NASA Chief: 'Let's Go Save the Hubble'
• Canadian Robot Top Choice for Hubble Servicing Mission
• Study: Hubble Robotic Repair Mission Too Costly
• NASA Prepares for Possible Shuttle Mission to Save Hubble
• NASA Review: Hubble Headed For Deorbit-Option Only
• Health Checkup: Engineers Work to Stall Hubble's Death
• Hubble Puzzle: How Safe is a Shuttle Servicing Mission?  

Podcast: Hubble: The First Great Space Observatory