By Dr David Whitehouse BBC News Online science editor

The World Space Observatory would help protect ultraviolet astronomy

That is the claim of a University of Leicester, UK, astronomer who is calling for a replacement called the World Space Observatory to be built.

Nasa says visits to the HST are to stop due to shuttle safety concerns.

Because it is in space, Hubble is the only telescope able to observe in the ultraviolet region of the spectrum.

Only from orbit

Speaking at the UK National Astronomy Meeting being held in Milton Keynes, Professor Martin Barstow said astronomers were very concerned that when Hubble ceased operation they would lose the clear images it provided of the Universe as seen in ultraviolet light.

Although Hubble is famous for its spectacular images in the visible and infrared, it also does important work with detectors sensitive to radiation at shorter wavelengths, including the ultraviolet.

These can only be carried out in space because the Earth's atmosphere acts to filter out higher energy light.

The successor to Hubble - the James Webb Space Telescope - is not due for launch until 2011 at the earliest, and it will not have Hubble's ultraviolet capability.

Professor Barstow pointed out that ultraviolet astronomy had already produced significant advances in the understanding of our own galaxy, stellar evolution and the behaviour of our own Sun.

New approach

"When Hubble finally fails, access to one of the most important parts of the spectrum will end for the foreseeable future," he said.

The only hope, he added, was for an international consortium of astronomers to fill the gap with the "World Space Observatory", a proposed telescope that would make more sensitive ultraviolet observations than Hubble.

He maintained it could be designed and built in about five years given the right political and financial backing.

"The World Space Observatory is a completely new approach to carrying out space science, spreading the overall costs across a much larger number of countries than in the past.

"At the moment, it is the only potential replacement for Hubble in the ultraviolet and it is essential that the worldwide community supports the project," he said.