"Not since Galileo turned his telescope towards the heavens in 1610 has any event so changed our understanding of the Universe as the deployment of the Hubble Space Telescope."
By Rachel Clarke
BBC News Online in Washington
So says Nasa's official introduction to the Hubble, but officials at the US space agency are now planning its demise and that is upsetting many scientists.
Scientists have glimpsed new galaxies through Hubble
The facts are straightforward. Launched in 1990, the telescope was always destined to have a limited life. Planning is well under way for a new space telescope - the James Webb - to launch in 2011 and the Hubble mission is slated to end by 2010.
But it need not be that way, argue Hubble's supporters. Such are the passions surrounding the subject that Nasa has chartered a panel of experts to determine the best way to manage the transition.
The panel has already received hundreds of e-mails offering suggestions and raising concerns about the changes.
Edward Cheng, who worked as a development scientist on the Hubble programme, told BBC News Online that there were simple reasons why many astronomers felt so strongly.
"They don't know a world without Hubble," he said. Such is the volume of data that the telescope has been able to gather, that scientists' first reaction now when faced with an idea or question is always "What can Hubble tell us?", he explained.
Scientists say Hubble captured the "best ever" image of Mars
Gave us the age of the Universe
Provided proof of black holes
Gave first views of star birth
Showed how stars die
Caught spectacular views of Comet Shoemaker-Levy 9's collision with Jupiter
Confirmed that quasars are galactic nuclei powered by black holes
Gathered evidence that the expansion of the Universe is accelerating
Of course Hubble was not always such a font of information. Soon after its launch an aberration was discovered on the crucial primary mirror. It was three years before corrective optics were designed, made and installed.
But the years since then have made all the difference, according to Sir Martin Rees of Cambridge University, who is England's Astronomer Royal and a member of the transition panel.
"There's no doubt it has been a flagship programme for Nasa for more than the last decade," he told BBC News Online.
And the data which has kept scientists so busy has also - in refined form - caught the imagination of the public with clues to the "big questions" like the origin of the Universe.
"Nasa has an awareness that the big questions are the questions which are not only of great scientific importance but they are also the ones the public is interested in," Sir Martin said.
Down to Earth
But while the scientific community wants to make the best use of the good will and interest that Hubble has generated, as well as the investment already made, harsh facts have to be faced.
Anne Kinney, director of Nasa's astronomy and physics division, brought a room full of Hubble fans back down to Earth when she stressed there was no way that Nasa would be able to recover Hubble to show off in a museum as had once been planned.
Astronaut safety must come above scientific goals, Nasa says
She told the public meeting in Washington DC that the loss of the Columbia shuttle and its seven crew in February had placed more emphasis than ever on the desire not to put astronauts at unnecessary risk.
At least one more visit to the telescope will be necessary to attach rockets to allow it to be brought out of orbit safely, but the extra danger of using that visit to recover Hubble is unacceptable given that it would bring no scientific advantage, she said.
Nasa has also rejected the idea of pushing Hubble into a higher orbit - "We are not prepared to leave a problem for future generations" - or to just leave Hubble working until it eventually fell by itself - "We are not going to be in a position where our missions cause deaths on Earth," she said.
Risk v gain
With manned spaceflight on hold while the shuttle disaster is investigated, no future mission can even be guaranteed to Hubble - named after Edwin Hubble who pioneered the study of galaxies in the 1920s.
But Dr Cheng said he expected Nasa to recover from the Columbia tragedy - just as it went back to work after the loss of the Challenger in 1986.
"There is a price to be paid for discovery," he said, adding that the question of acceptable risk should be put to astronauts, not to scientists or managers.
"To them it's discovery, it's their life. They know they are taking risks but they will do that if there is a lot to gain."
Adding propulsion to the Hubble so it could be destroyed harmlessly as it fell back to Earth might not be worth it to an astronaut, but servicing Hubble so it could continue to be used might be, he said.
The regeneration of Hubble through missions which have added new tools and capability has been a key feature of its success.
The observatory now in orbit uses cutting-edge technology, not merely equipment developed when the telescope was being built on Earth during the 1980s.
A camera upgrade resulted in this picture of the Cone Nebula
Dr Cheng says he believes Hubble could continue to be a useful tool until 2020 when irreplaceable parts such as the mirrors could be expected to degrade.
"Nothing made by humans goes on forever and Hubble is no exception. It has a time [to end]. That time is not now," he said.
Part of the desire to keep Hubble operating is simply not wanting to do without something to which you have become accustomed - but there is more to it than that.
The James Webb telescope will be able to do things which Hubble cannot, such as look through clouds of space dust. But it has no ultra-violet optical capacity and the end of Hubble will leave an entire community of scientists without their primary research tool.
Hubble is said to give Nasa 33% of its results for less than 2% of its budget, and its fans would like to see its life extended as long as possible.
Steven Beckwith, of the Space Telescope Science Institute, pointed to Hubble's successes, including many which had not been predicted when it was being developed.
"Dark energy was not even something people were talking about observationally in 1996/97," he said.
"One of the most remarkable things is extra-solar planets - there were no extra-solar planets discovered before Hubble's launch."
Many more things could still be there to be found, he said.
"Hubble has unique capabilities that provide compelling science opportunities not just to 2010 but beyond. Hubble has not reached the limits of its capability."
But even if the will was there, budgets are limited and Hubble's universe looks to be strictly limited.