NASA is on target for its launch of the space shuttle Atlantis on its final mission to service the Hubble telescope, the US space agency said on Sunday.


"Atlantis is ready to fly," said the test director, Charlie Blackwell-Thompson, adding that the countdown to launch was proceeding on schedule, with lift-off expected on Monday at 2.01pm (1801 GMT).

Weather forecasters said there was a 90 per cent chance of favourable conditions for the launch from Kennedy Space Centre in Cape Canaveral, Florida.

The 11-day shuttle mission aims to provide the fifth and final maintenance operation to the Hubble before the shuttle fleet is retired, and if successful NASA has said the mission would extend the stargazer's life by at least five years.

Hubble's servicing will entail five spacewalks, each lasting up to seven hours. Crew members plan to replace the telescope's six gyroscopes and batteries and upgrade its optical instruments.

Launched in 1990, Hubble has long been considered the greatest tool in the history of astronomy.

Using powerful instruments to peer into deep space, it has provided profound insights into the origins and evolution of the universe.

But NASA experts stressed that the Atlantis mission carries heavy risks.

"This will be the most challenging servicing mission that's been faced by our astronauts in terms of the total amount of work," said Preston Burch, mission manager.

A journey to the 11-ton Hubble carries more risk of being hit by space debris or micrometeorites than a flight to the International Space Station, as the telescope orbits at almost twice the height of the ISS.

Officials hope the mission will allow Hubble to keep functioning until 2014, when it is due to be replaced by the James Webb Space Telescope, a highly sophisticated space telescope with an eagle-eye camera.