Nasa scientists and astronauts have outlined details of a "challenging mission" to repair and upgrade the Hubble Space Telescope this year.

The Atlantis Space Shuttle is scheduled to lift off in August on the Hubble servicing mission designated STS-125.

The craft will carry a crew of seven astronauts and a cargo of equipment, tools and instruments to service the telescope which orbits 350 miles above the Earth.

Alan Stern, associate administrator for the Science Mission Directorate at Nasa, said: "Hubble is a national treasure, and Nasa is looking forward to seeing it receive this tune-up and upgrade.

"Americans are going to be excited when they see the results of this exciting shuttle mission flower into new discoveries about the Solar System and the larger universe.

"It doesn't get much more exciting than sending a team of astronauts and sophisticated high-tech instruments to make the Hubble better than ever before. "

The 11-day mission will include five spacewalks during which astronauts will install two powerful science instruments, new gyroscopes and batteries, and thermal blankets to extend Hubble's operational life until at least 2013.

If all goes well, a degrading Fine Guidance Sensor unit, one of three aboard Hubble, will be replaced with a refurbished unit to help maintain the telescope's ability to point and focus on objects throughout the universe.

"As an astronaut and an astronomer the opportunity to go back to Hubble is more than a dream come true," said John Grunsfeld, the mission's lead spacewalker.

"This mission promises to be quite challenging, and Nasa has put together the most experienced Hubble crew ever with three Hubble veterans.

"The crew and mission team are in full throttle training, looking forward to launch and the hard work of servicing Hubble."