SpaceX set to launch with cargo for International Space Station

And, he added during a pre-launch briefing, it's nice to have a US-based carrier back in the mix. It gives the US more flexibility in getting replacement parts to the space station in a timely fashion. Moreover, "shipping and customs can kill you when you're trying to get [parts] overseas" to ride on Russian, Japanese, or European cargo craft.

"We're excited to have the vehicle coming up to visit the ISS," he says.

The launch is set for 8:35 p.m. Eastern Daylight Time Sunday, although the weather forecast gives the mission a 40 percent chance of a scrub because conditions could violate launch requirements. Once off the pad, Dragon should take about 53 hours to reach the station, said Gwynne Shotwell, SpaceX's president. The capsule is expected to remain hitched to the space station for about three weeks.

Because Dragon is trying to rendezvous with another spacecraft, it has a very narrow span of time in which it can launch each day. The mission can't wait an hour for the weather to clear if it's not acceptable at launch time. If tonight's launch is postponed, SpaceX will have opportunities Monday and Tuesday for launches, days when the weather is expected to be more favorable for a launch.

In addition to the weather, NASA is eying some space debris that may require the space station to move out of the way. The debris is expected to make its closest approach to the station on Monday at 7:02 a.m. Eastern Daylight Time. Any change in the station's orbit would be slight, Mr. Suffredini said. But it would require Dragon to work a bit harder to catch up with the station.

As SpaceX was making its final preparations for today's launch last week, Orbital Sciences Corporation – the second company slated to carry cargo to the space station – cleared a milestone enroute to its first test launch.

On Oct. 1, it rolled out the first stage of its Antares rocket to the launch pad at NASA's Wallops Island Flight Facility on the Virginia coast. By the end of October, NASA officials say, they anticipate the first fuel loading and unloading tests, as well as the first, brief test of the rocket's motors as the first stage stands on the pad. In December, the company plans its first test flight, followed by the first demonstration flight to the space station.

NASA and Orbital Science haven't decided on timing for the demonstration flight, Suffredini says. "But I'd be surprised if it was before late February or early March."

IN PICTURES: Launch of SpaceX's Falcon 9 Rocket

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