For the first time in almost a year, NASA was set to launch a space shuttle Saturday on a mission that will test whether the space agency has reduced the risks of flying in the 25-year-old vehicles.
As the astronauts finished strapping into the space shuttle one by one, thunder clouds moved closer to the Kennedy Space Center and threatened to delay the 3:48 p.m. EDT (1948 GMT) blastoff of Discovery in what would be only the second launch since the Columbia disaster in 2003.
Dressed in their neon orange spacesuits, the astronauts waved and gave thumbs up as they boarded the astrovan to go to the pad.
Vice President Dick Cheney was among the dignitaries expected to attend the launch.
A last-minute technical problem popped up Saturday morning, with the failure of a heater used to keep propellant from freezing in a firing thruster. The thruster is not used during launch, but it can control the shuttle's position in space and during a rendezvous with the international space station.
"It's not a show-stopper, in terms of rendezvous," said NASA spokesman Kyle Herring. "You can manage it."
The countdown proceeded as normal, and NASA was unsure what effect it would have on the launch. Space agency managers have said they want all four thrusters working properly.
Fueling, completed under three hours, showed that four new fuel tank sensors worked properly. The four sensors designed to prevent the main engines from running too long or not long enough during the climb to space had been replaced after one of them gave an electrical reading that was slightly off. The swap-out pushed back Discovery's launch in May.
The launch Saturday will test NASA Administrator Michael Griffin's decision to go ahead with the mission despite the concerns of two top agency managers who fear foam flying off the fuel tank might harm the space shuttle, reports AP.
Outgoing US President Donald Trump does not accept the outcome of the November election. Trump has also refused to attend Joe Biden's inauguration ceremony on January 20