Washington  - The fifth and last mission to repair the ageing Hubble Space Telescope could launch a day earlier than planned, officials at the US space agency said Thursday.

The space shuttle Atlantis was to take off from its Florida launch site on May 12 and could likely take off at 2:01 pm (1801 GMT) on May 11, officials at the National Aeronautics and Space Administration (NASA) said.

"I'm fairly confident that we can make a May 11 launch date," said LeRoy Cain, deputy manager of the Space Shuttle Programme.

The earlier launch was to avoid a scheduling conflict at the Kennedy Space Centre in Cape Canaveral, Florida, and officials said they would know within a week if the May 11 date was feasible.

With an earlier launch date, Atlantis will have at least two additional chances - on May 12 and 13 - to lift off. If it can't launch by May 13 then NASA will have to wait until May 22 because of a scheduled military operation at the Cape Canaveral Air Force station.

The risky mission to repair Hubble has been plagued by delays, with NASA indefinitely postponing it because of problems with the orbiting telescope's mechanisms. A launch slated for October 14 was cancelled.

When Atlantis finally lifts off in May, its seven-member crew will refurbish and upgrade the telescope with state-of-the-art instruments that are expected to improve Hubble's eyesight 90-fold.

The crew will perform five spacewalks and it is expected that Hubble's operational lifespan will be extended through at least 2014, NASA said.

"Tomorrow is Hubble's birthday - she turns 19," said crew member John Grunsfeld, "so we should all celebrate."

NASA reluctantly scheduled the service mission under pressure from space enthusiasts who were alarmed at the prospect that the ageing Hubble would shut down for years before a new telescope could be launched - the James Webb Space Telescope, slated for launch in 2011.

Finally in 2006, NASA caved in to pressure from Congress and the scientific community and slated a repair mission. (dpa)