The US space agency has set a tentative date of May 12 for the liftoff of the Atlantis space shuttle, on a long-delayed service mission to the Hubble telescope, NASA announced.

The original launch, scheduled for October, was put off after a unit that collects, formats and sends data back to the ground from Hubble failed.

"Since then, engineers have been working to prepare a spare... They expect to be able to ship the spare, known as the Science Instrument Command and Data Handling System, to NASA's Kennedy Space Center in Florida in spring 2009," NASA said in a statement sent out late Thursday.

The flight of Atlantis shuttle STS-125 to Hubble will be the last to service the aging telescope, which is due to be replaced in 2013 by a highly sophisticated space telescope with an eagle-eye camera.

Scientists hope the new telescope will help to lift the veil off the mysteries and origins of the universe.

The servicing mission will last 11 days and feature five spacewalks to extend Hubble's life into the next decade by refurbishing and upgrading Hubble with state-of-the-art science instruments and replacing failed units, NASA said.

The seven-month delay to the service mission will cost NASA around 70 million dollars, based on information given by officials at the space agency in September.

Then, they said that each month that the mission was put off would cost the agency around 10 million dollars, but they also insisted the added expense of the program was not a reason to abandon Hubble.

Launched 18 years ago, Hubble revolutionized astronomy by peering deep into the universe, beaming back dazzling images free of the distortions from Earth's atmosphere.

Orbiting 575 kilometers (360 miles) above Earth, Hubble has enabled scientists to better measure the age and origins of the universe, observe distant supernovas, and identify and study bodies in and outside the solar system.