Nasa has set targets SpaceX must meet to stay in the COTS programme
A key milestone has been reached in the development of the rocket that may soon be flying cargo and astronauts to the International Space Station (ISS).
The SpaceX company has conducted a test-firing of its Falcon 9 vehicle.
The demonstration in Texas meets a target laid down by the US space agency (Nasa) which has given SpaceX some "seed" funding.
Nasa hopes the Falcon 9 can help fill the mission gap that will exist while it develops a successor to the shuttle.
That successor - known as Ares/Orion - is not expected to be flying before 2015, leaving a five-year break from shuttle retirement in 2010 during which the Americans would be reliant on international partners for all their ISS transportation needs.
It is anticipated that the Falcon 9 will make its maiden flight in the coming months - certainly by the first quarter of 2009. Initially, it will just loft satellites, including the British-built-and-operated Hylas broadband and TV spacecraft.
But SpaceX wants to be using the vehicle to launch its Dragon capsule very soon afterwards. The capsule is being designed to carry both supplies and people to the space station.
Falcon 9 could still complete a mission if one of its nine engines failed
The latest testing saw the first nine-engined firing of the Falcon 9's first stage (it will have two stages, both of which will be reusable). Firings were completed on Thursday and Friday, at the Texas Test Facility outside McGregor.
SpaceX said the engines, at full power, consumed 1,500kg (3,200lbs) of fuel and liquid oxygen per second, and generated a thrust of 3,700 kiloNewtons (832,000lbf) - four times the maximum thrust of a 747 aircraft.
California-based SpaceX and Virginia-based Orbital Sciences Corporation have both received development money from Nasa under its Commercial Orbital Transportation Services (COTS) competition.
The agency wants to see the "market" take over many of the low-Earth orbit transportation roles traditionally done "in house" at Nasa; and the hope is that the commercial sector can service the space station at a lower cost than has been the case to date.
This would leave the US space agency free to concentrate its technology - and more of its resources - on activities further afield, going to the Moon and to Mars.
In its "heavy" configuration, Falcon 9 will have the capacity to take about 30 tonnes of payload into low-Earth orbit - comparable to what the shuttle is able to achieve now.
SpaceX is about to launch its smaller Falcon 1 rocket in the coming days.
The company is led by the internet billionaire Elon Musk.