NASA scrubbed the last scheduled launch of the space shuttle Endeavour on Friday, citing problems with failed heaters. Buses carrying the astronauts were headed to the shuttle when the decision was made and were turned around.
The space agency said the repairs will take time and it will set a new launch date this week. Such delays are not uncommon in the shuttle program; launches are often postponed and rescheduled.
The mission commander, Navy Capt. Mark Kelly, is the husband of Rep. Gabrielle Giffords, D-Ariz., who was seriously injured in January's Tuscon shootings. Giffords had been scheduled to watch the launch in Florida along with President Obama and his family.
Endeavour is loaded with a $2 billion particle physics detector that will seek out antimatter and dark energy across the universe. Many in and outside of NASA say the experiment, if successful, could validate science operations at the decade-old orbiting lab.
As many as 750,000 people were expected to crowd nearby coastal communities for the liftoff, the Associated Press reported. The last shuttle program mission is scheduled for June 28. After that, the United States will rely on Russian spacecraft to get astronauts in and out of orbit.
Kennedy Space Center was groaning with 45,000 guests, including more than three dozen members of Congress, at least two former NASA administrators, and a score of high-level academic and space industry officials, who planned to observe Friday's launch.
NASA is ending the shuttle program this summer, after the last trip by Atlantis. Obama is pushing private space initiatives and encouraging robotic scientific mission.