NASA hasn't seen this much launch jitters since the space shuttle program ended last summer.
On Saturday, a private company was set to make history by launching a capsule loaded with supplies to the International Space Station. The rocket maker known as SpaceX _ Space Exploration Technologies Corp. _ hopes to join a short list of governments in flying to the orbiting lab.
On the eve of this new commercial era, NASA officials described it as "a seminal moment" and extremely important mission, while SpaceX leaders said they were awe-struck over what they were about to undertake.
"There's no question this is a historic flight," SpaceX President Gwynne Shotwell said at a news conference Friday.
Only Europe, Russia, Japan and the U.S. have sent a spacecraft to the space station, she noted. "So yeah, we really respect having the opportunity to attempt this," she said.
The SpaceX Falcon 9 rocket was scheduled to blast off from Cape Canaveral at 4:55 a.m. Forecasters put the odds of good weather at 70 percent.
The Dragon capsule atop the rocket contains a half-ton of space station supplies. The capsule will perform practice maneuvers around the space station on Monday before NASA gives a "go" for docking on Tuesday.
The California-based SpaceX _ formed by PayPal co-founder Elon Musk _ is the first of several competing companies to actually get this close to launching a vessel to the space station. For now, it's supplies. Within three or four years, the goal is to have astronauts on board so Americans no longer have to hitch expensive rides on Russian rockets.
Well before Atlantis made the final shuttle flight last July, NASA began handing over space station delivery duties to the private sector. It is more cost-effective that way, said NASA's director of commercial spaceflight development, Phil McAlister, and enables the space agency "to take our savings and plow them into" other venues such as interplanetary exploration.
SpaceX has launched a Falcon 9 rocket just twice before, once with a Dragon capsule that reached orbit. The company has never gotten down to zero and flown on the first try, Shotwell noted, putting the odds of accomplishing that Saturday _ with a scant one-second launch window _ at 50-50 or a bit better.
A Dragon capsule blasted into orbit in December 2010. What was remarkable was the safe recovery of that capsule following its brief solo flight around the world; it splashed into the Pacific.
If all goes well, the newest Dragon also will parachute down off the California coast, returning experiments and equipment two weeks after reaching the space station.
Both NASA and SpaceX stress this is a test flight, with the main objective being to learn.
"Hopefully, we learn a lot and, hopefully, we make a lot of progress," Shotwell said.