Shuttle astronauts would do a better job of upgrading the ailing Hubble Space Telescope than robots, a panel of space experts has said.
Hubble needs regular maintenance
The panel was set up to look at ways of servicing Hubble, which needs replacement gyroscopes and batteries and some new instruments.
A robotic mission was favoured by Nasa chief Sean O'Keefe in the aftermath of the Columbia space shuttle disaster.
Nasa said it would study the report but would not comment on its findings now.
"A shuttle servicing mission is the best option for extending the life of the Hubble telescope and ultimately de-orbiting it safely," said Louis Lanzerotti, head of the expert panel charged with investigating how to fix the 14-year-old orbiting observatory.
Mr O'Keefe cancelled a planned shuttle servicing mission to the telescope in January due to safety concerns after the break-up of space shuttle Columbia on re-entry.
But following pressure from astronomers and fans, the Nasa chief requested proposals for a robot that could service the telescope.
Now, Dr Lanzerotti and other panel members have decided the plan for a robotic mission is more technologically risky - and far less likely to actually fix Hubble.
They told a news conference that the risk to astronauts in a shuttle repair mission was about the same as that involved in travelling to the International Space Station (ISS).
No shuttles have flown since the Columbia accident on 1 February 2003 killed seven astronauts. Flights are not expected to resume before next May.
Any shuttle mission to Hubble would have to be slotted into a schedule of flights already planned to the ISS, said panel member Richard Truly.