By Dr David Whitehouse
BBC News Online science editor
An influential panel of researchers says the US space agency (Nasa) should not rule out a space shuttle mission to repair the orbiting Hubble telescope.
"The most important telescope in history"
Nasa requested the report through the US National Academy of Sciences after being criticised for the decision to ban future shuttle servicing flights.
The ban was deemed necessary because of new safety rules brought in following the loss of the space shuttle Columbia.
The report says it is vital to repair Hubble by manned or unmanned missions.
Astronauts or robots
Nasa's January decision to cancel the fourth shuttle mission to service the ailing Hubble Space Telescope (HST) led to a welter of criticism from, amongst others, US politicians; and this prompted the agency to seek a second opinion.
The full report, produced by prominent scientists and engineers from the National Academy of Sciences, is due in the Autumn but the panel has released some of its early thoughts.
It says that according to its interpretation of the recommendations of the Columbia Accident Investigation Board (CAIB), it does not believe that a shuttle flight to the HST has been completely ruled out.
Consequently, it does not want Nasa to foreclose the shuttle option to service the HST.
Its adds: "At the same time that Nasa is vigorously pursuing development of robotic servicing capabilities, and until the agency has completed a more comprehensive examination of the engineering and technology issues, including risk assessments related to both robotic and human servicing options, Nasa should take no actions that would preclude a space shuttle servicing mission to the Hubble Space Telescope."
Hubble's deepest view of the cosmos was revealed earlier this year
The panel says it would be happy to see the servicing done by either a manned mission or by a robotic spacecraft - just as long the HST is saved.
Without further servicing, say astronomers, the HST is unlikely to survive for more than three or four years.
The panel says a further servicing mission should include both the replacement of the present instruments with the two instruments already developed for flight - the Wide Field Camera-3 and the Cosmic Origins Spectrograph - as well as engineering objectives, such as gyroscope and battery replacements.
Such a servicing mission, the report continues, would extend the life of this unique telescope and maximise its productivity.
In a statement on the Hubble report, Nasa's Administrator Sean O'Keefe said he deeply appreciated the panel's comments - but he gave no indication he would change his mind on manned servicing.
"We agree with the committee's view that the Hubble Space Telescope is arguably the most important telescope in history. Nasa is committed to exploring ways to safely extend the useful scientific life of Hubble.
"The challenges of a robotic mission are under examination and we'll continue our exhaustive and aggressive efforts to assess innovative servicing options," he says.
"Nasa will evaluate proposals we expect to receive shortly. Along the way, we'll keep options open to assure the best possible outcome.
"The Hubble Space Telescope is a national treasure. Just as we are committed to meeting the recommendations and findings of the CAIB and returning the space shuttle to safe flight, we're committed to doing everything possible to safely extend the scientific life of this valuable asset."