With a forecast of near-perfect weather, NASA's Hubble Space Telescope scientists and managers were euphoric as they awaited Monday's planned launch of shuttle Atlantis on the final trip to the orbiting observatory.
The anticipation was all the greater given all the years of mission delays.
"To be within one day of it is remarkable, unbelievable and I have to persuade myself I'm not dreaming," senior project scientist David Leckrone said on Sunday.
"But I walk outside and I see that beautiful bird on the pad (Atlantis) and I see the gorgeous weather, and we're going to get off on Monday and it's going to go splendidly. I just feel it."
Earlier on Sunday, meteorologists issued an improved forecast, putting the odds of good launching weather at 90 per cent, about as good as it gets. Only a slight chance of rain is expected at the emergency landing site in Spain.
Atlantis is poised to blast off with seven astronauts just after 2 pm. EDT (1800 GMT).
The 19-year-old Hubble needs new batteries, gyroscopes, cameras and other equipment that NASA hopes will keep the telescope operating -- at a higher than ever scientific level -- for another five to 10 years.