US space agency (Nasa) chief Mike Griffin says shuttle astronauts will be sent to service the Hubble telescope.
HUBBLE SPACE TELESCOPE
Named after the great US astronomer Edwin Hubble
Launched in 1990 into a 600km-high circular orbit
Equipped with a 2.4m primary mirror and five instruments
Length: 15.9m; diameter: 4.2m; Mass: 11,110kg
Observations have probed about 24,000 celestial objects
Made more than 93,000 trips around our planet
Generates about 10 gigabytes of data each day
The orbiting observatory has astounded astronomers and the public alike with its amazing pictures of the cosmos, but its systems are beginning to fail.
Dr Griffin told Nasa employees that recent modifications to the shuttle launch system meant it was now safe to send a crew to work on Hubble.
The mission, which will use the shuttle Discovery, should launch in 2008.
"We are going to add a shuttle servicing mission - to the Hubble space telescope - to the shuttle's manifest to be flown before [the orbiter] retires," Dr Griffin told an audience at the Goddard Space Flight Center in Maryland where the Hubble programme is managed.
Without servicing, the observatory is not expected to last more than two or three years.
Its batteries and gyroscopes, which are used to point the telescope, are degrading and they will now be replaced.
The shuttle crew will also install two new instruments: the Wide Field Camera 3 (WFC3), and the Cosmic Origins Spectrograph (COS). The new instruments will improve significantly Hubble's ability to probe distant, faint objects in the early Universe.
Haven of safety
The servicing mission should extend Hubble's orbital lifetime to at least 2013, by which time Nasa will be getting close to launching a successor: the James Webb Space Telescope.
Dr Griffin's decision reverses that of his predecessor, Sean O'Keefe, who cancelled the planned visit in the wake of the Columbia shuttle disaster in 2003.
The orbiter's heat shield had been damaged during launch and the ship was destroyed as it returned through the atmosphere for landing 16 days later.
Mr O'Keefe had implemented a safe-haven policy for subsequent shuttle crews, which meant if their orbiters became damaged in a similar way they could stay on the International Space Station until rescued.
A Hubble servicing mission was a casualty of this policy as shuttles do not carry sufficient fuel to move between the orbits of the observatory and the station.
Dr Griffin's green light will now require Nasa to prepare an alternative rescue strategy if Discovery finds it has sustained catastrophic damage on the climb to orbit.
This would involve sending up another shuttle to attempt a ship-to-ship transfer of astronauts.
A 'PIT STOP' IN SPACE
See how the Discovery shuttle will grapple Hubble
"There are very small odds that we would have a problem on ascent for which the remedy would be a launch-on-need shuttle - a rescue shuttle," explained Dr Griffin.
"But against the very small probability that that could occur [we] have made the decision that we will carry that rescue option in the manifest; and that that rescue mission will consist of a shuttle waiting on the other pad from which we launch the Hubble mission."
Record of discovery
The news of a servicing mission was greeted with jubilation by astronomers worldwide. The multi-billion-dollar observatory project has made a remarkable contribution to our understanding of the origin and evolution of the Universe.
Hubble has obtained the deepest views of the cosmos, finding high-interest objects for other observatories to investigate in detail.
Its studies of the Universe's expansion early in its mission dramatically refined the best estimates for the age of the cosmos. Its pictures have also produced definitive proof for the existence of black holes and confirmed theories of planetary formation.
Scientists expect an upgraded Hubble to continue making groundbreaking discoveries.
"Today Hubble is producing more science than ever before in its history. Astronomers are requesting five times more observing time than that available to them," said Bob Fosbury, head of the European Space Agency's Hubble group.
"The new instruments will open completely new windows on the Universe. Extraordinary observations are planned in the coming years, including some of the most fascinating physical phenomena ever seen: investigations of planets around other stars, digging deeper into the ancestry of our Milky Way and above all, gaining a much deeper insight into the evolution of the Universe."
The Maryland Senator Barbara Mikulski, who has campaigned for a servicing mission, called Tuesday "an exceptional day".
"It's a great day for science, a great day for discovery, a great day for inspiration; because that's one of the things Hubble has meant to so many people," she told the Goddard meeting.
SERVICING THE HUBBLE SPACE TELESCOPE
Shuttle Discovery will grab Hubble with a robotic arm and pull it on to a work platform to allow astronauts easy access to its interior
Hubble has six gyroscopes that are critical to its control and pointing systems. These have started to fail and all will have to be replaced
Six new batteries will rejuvenate the electrical system; astronauts will attach new thermal blankets to insulate sensitive components
The telescope has two instrument bays; the COS and WFC3 will be slid into racks made vacant by the removal of older instruments
An attempt will also be made to repair the Space Telescope Imaging Spectrograph (STIS) which stopped working in 2004