Space Exploration Technologies (SpaceX) is blaming the overwhelming amount of work involved in developing its Falcon 9 rocket and Dragon capsule for a six-month delay in the new vehicles' maiden flight.

The Falcon 9 is designed to place 9,900kg (21,800lb) into low Earth orbit and its Dragon capsule will carry more than 2,500kg of cargo or a crew of up to six to LEO.

The rocket and capsule's development is, in part, being funded by the NASA Commercial Orbital Space Transportation Services (COTS) programme, under which SpaceX won a funded space act agreement in August 2006.

Previously scheduled for a US government-funded maiden demonstration flight in the fourth quarter of 2008 with two more flights before the end of the year, including the first COTS demonstration flight, the first launch is now expected late in the first quarter of 2009 and subsequent COTS and commercial flights in the second quarter.

"It is the enormous amount of work to get done," says SpaceX chief executive Elon Musk. "I can't honestly point to any one thing. It is an array of things - structural qualification, software and hardware testing. We have to complete it all for Dragon and for the Falcon 9, and prove it to the NASA folks."

Another cause for the delay, says Musk, is the regulatory work surrounding the company's new launch site at Cape Canaveral's pad 40, from where the Falcon 9 will operate. SpaceX's Falcon 1 rocket, which has been launched twice but suffered failures, operates from Kwajalein Atoll in the Pacific Ocean. This was also going to be Falcon 9's launch site before it switched to Cape Canaveral.

NASA commercial crew and cargo programme manager Alan Lindenmoyer revealed the Falcon 9 delay for COTS flights when speaking at the AIAA 3rd space exploration conference in Denver, Colorado on 26 February.

The following day, SpaceX announced it had completed qualification testing of the regeneratively cooled version of its Merlin 1C engine that will now power the Falcon 1 rocket. Falcon 1 has a 570kg to LEO capability and its third demonstration flight is scheduled for April.

Falcon 1's first three manifested launches for 2008 are: the demonstration flight, a new contract for a June mission, and then the launch of the Malayasian government's Razaksat satellite.