Lots of nail biting on the eve of a historic launch

With the first commercial spacecraft to attempt docking with the International Space Station waiting on the launch pad, nerves and excitement are high. And hours before the historic launch, officials from NASA and private company SpaceX are managing expectations.

"It bears repeating that this is a test flight," said director for NASA Commercial Spaceflight Development Phil McAlister in a press conference today, where he was reluctant to even use the word "success". "NASA views test flights as learning opportunities."

The cargo-carrying Dragon capsule has a long list of firsts to achieve in the next few days. It's scheduled to launch at 4:15 am eastern time tomorrow, and will spend the first 24 hours catching up with the International Space Station in low-Earth orbit. At around hour 40, it will begin a choreographed dance around the space station to make sure it's sufficiently under control to attempt docking. Astronauts on the space station will test communications with the Dragon and can abort the mission at any time.

If everything goes well, Dragon will dock to the space station by 75 hours after launch, early morning on Tuesday 22 May.

"If successful, there's no question this is the historic flight," said SpaceX president Gwynne Shotwell. "I think we're going to be biting off our fingers between now and hour 75."

Shotwell also stressed that this is a test flight and things could go wrong.

"Success is not going to mean the success of the commercial space industry, and failure is not going to mean the failure of the commercial space industry," she said. "We'd hope that every flight is successful, that would make my job incredibly easy. But I don't want to say that, I don't think that's realistic."

Despite that, she has an optimistic view of the future. The company has 17 launches planned in the next three years, and could be bringing astronauts into space as early as 2015, Shotwell says - although McAlister says it may be more like 2017 before they're certified to fly NASA astronauts.

And the transition from big government organizations to private companies navigating the skies may be inevitable, he added.

"Once we get the private sector out there, there will be no turning back," he said. "[Spaceflight] will no longer be subject to the prevailing political winds. It will just push further and further out, no more looking backwards, only looking forwards."