Cape Canaveral - SpaceX on Tuesday launched its Dragon space capsule toward the International Space Station, becoming the first private firm to attempt a test mission to the orbiting lab.
"Three, two, one and launch of the SpaceX Falcon 9 rocket, as Nasa turns to the private sector to resupply the International Space Station," said Nasa commentator George Diller, as the spacecraft blasted off at 03:44.
The test flight - which is set to include a fly-by and berthing with the station in the coming days - aims to show that private industry can restore US access to the ISS after Nasa retired its space shuttle fleet last year.
No humans are travelling aboard the Dragon, but six astronauts are already at the $100bn space lab to help the capsule latch on, to unload supplies and then restock the capsule with cargo to take back to Earth.
California-based SpaceX, owned by billionaire internet entrepreneur Elon Musk, is the first of several US competitors to try sending spacecraft to the ISS with the goal of restoring US access to space for human travellers by 2015.
The company successfully test-launched its Falcon 9 rocket in June 2010, then made history with its Dragon launch in December of that year, becoming the first commercial outfit to send a spacecraft into orbit and back.
Its reusable Dragon capsule has been built to carry both cargo and up to seven crew members.
Until now, only the space agencies of Russia, Japan and Europe have been able to send supply ships to the ISS.
The three-decade US shuttle programme, which ferried astronauts and cargo to the research outpost, ended for good in 2011, leaving Russia as the sole taxi to the ISS until private industry comes up with a replacement.
The Saturday launch attempt was scrubbed at the last second when computers detected high pressure in the central engine of the Falcon 9.
SpaceX engineers discovered the root cause was a faulty check valve and repaired it the same day.
The US space agency has given SpaceX about $390m so far of the total $680m that the company has spent on cargo development. SpaceX has a $1.6bn contract with Nasa for future supply missions.
$63m a ticket
Orbital Sciences Corporation is working on its own supply ship, with a preliminary launch scheduled for later this year, and has a $1.9bn contract with Nasa.
SpaceX also gets funding from Nasa for a separate effort to develop a commercial crew vehicle for carrying astronauts to space, along with competitors Blue Origin, Boeing and Sierra Nevada.
In a few years' time, SpaceX says it will be able to undercut the hefty price Nasa pays Russia for US astronauts to get a seat aboard the Soyuz space capsule - around $63m a ticket.
On 24 May, the spacecraft's sensors and flight systems are to undergo a series of tests to see if the craft is ready to berth with the space station, including a complicated fly-under at a distance of about 2.5km.
If Nasa gives the green light, the Dragon will then approach the ISS on 25 May in an attempt to berth with the station.
The astronauts on board the ISS will manoeuvre the station's robotic arm to help capture the capsule and attach it to the orbiting research outpost.
The hatch of the Dragon is set to open on 26 May for unloading and restocking. On 31 May, the Dragon is to detach from the station and make a safe landing in the Pacific Ocean off the coast of southern California.