SpaceX on Saturday aims to become the first private company to send its own cargo ship to the International Space Station, a feat that only a handful of world governments have pulled off.
The high-stakes mission is scheduled to begin before dawn on Saturday (4.55am, 8.55am GMT) with the launch of the unmanned Dragon spacecraft aboard a Falcon 9 rocket from Cape Canaveral Air Force Station in Florida.
The bid, if successful, would catapult the company owned by billionaire internet entrepreneur Elon Musk even further ahead in the race to fill the void left by the shuttle programme's end last year and restore America's access to space.
If not, it would be a setback for SpaceX, one of several companies working to build and launch a spacecraft that could tote astronauts to the ISS by 2015, and the first to attempt a cargo mission as a precursor to a manned flight.
"The attention given to this flight creates a set of high expectations and it's still a test flight but the consequences of failure would be very serious," said John Logsdon, space policy expert at George Washington University.
"NASA is putting a big bet on this succeeding."
SpaceX has so far received $381-million from NASA as part of a multi-year $1.6-billion contract to develop the capability to carry cargo to and from the ISS.
NASA has struck a similar deal with a second company, Orbital Sciences, though it has yet to attempt its first cargo mission.
The final flight of the US space shuttle programme in 2011 ended a 30-year era of US dominance in human spaceflight and left Russia as the only nation capable of transporting both astronauts and cargo to the International Space Station.
SpaceX is already further ahead than any of its other competitors in the private space race, which also include aerospace giant Boeing, the Nevada-based Sierra Nevada Corporation, and Washington state-based BlueOrigin LLC.
In 2010, SpaceX became the first commercial enterprise to successfully launch its space capsule into low-Earth orbit and back for a safe ocean recovery.
It has also been able to develop the Falcon 9 rocket launch vehicle at a third of the cost - $1.7-billion - it would have been for the US space agency to do the same - $4-billion - according to a NASA/Air Force Cost Model analysis.
"They are playing with their own money and they have real incentives to hold down costs," said Howard McCurdy, an author and space policy expert at American University in Washington.
"SpaceX is in the lead but whether or not they are going to wind up in the lead at the end, we don't know, that's what makes it fascinating to watch," he told AFP.
"It's like the Kentucky Derby. The winner may be halfway back. We are just going around the first turn right now."
If Saturday's launch is successful, the Dragon will attempt a fly-under of the orbiting lab at a distance of about 2.5 kilometres three days later, followed by a berthing bid with the ISS on day four of the mission.
Astronauts already aboard the ISS will use the space station's robotic arm to capture the gum-drop shaped Dragon capsule as it approaches and help it latch on, a high-precision manoeuvre given that both the lab and spacecraft are orbiting the Earth every 90 minutes.
On day five, astronauts already at the ISS will unload cargo from the Dragon and restock it with supplies to carry back to Earth.
After a two-week stay in space, the Dragon aims to return to Earth for a safe splashdown in the Pacific Ocean off the coast of California.
If weather or other reasons prevent Saturday's liftoff, another opportunity for launch opens on 22 May.
In addition to Russia, the space agencies of Japan and Europe also operate cargo ships to the ISS.