A US rocket company has blamed a design error for its latest failure to reach orbit, which caused the loss of three government satellites and human ashes, including the remains of Star Trek actor James Doohan and astronaut Gordon Cooper.

The two-stage Falcon 1 rocket, which blasted off from a Central Pacific atoll on Saturday night, separated as planned on its way to space, but leftover thrust after engine cutoff caused the first stage to fall back and hit the second stage, according to SpaceX.

The rocket, containing the remains of 208 people, dropped in the Pacific and was not recovered.

The family of Doohan, who played Scotty on the television show Star Trek, could not immediately be reached for comment.

A message left with Cooper's widow Suzan Cooper was not immediately returned. Cooper was one of the original Mercury astronauts who set a space endurance record by travelling 5.31 million kilometres aboard Gemini V in 1965.

The rocket also carried three small satellites for NASA and the US Defence Department. It was not immediately known how much the satellites cost. NASA lost a nanosatellite and an experimental solar sail.

Saturday's foiled launch was the third miss for SpaceX, which hopes to break into the low-cost space launch business.

Its 2006 maiden launch failed due to a fuel line leak. The rocket reached some 290km above Earth on its second try last year, but its second stage prematurely shut off.

The latest attempt used a different engine than the previous two tries. SpaceX said the new engine performed flawlessly, but the failure occurred because there was a short time gap - 1.5 seconds - between engine shutdown and stage separation.

Neither stage exploded, but they "got a little bit cooked", said internet entrepreneur Elon Musk, who founded SpaceX in 2002.

Musk said the problem could be easily fixed by increasing the timing between the two steps. Engineers did not detect the problem during testing because it was done at sea level, Musk said.

SpaceX plans to launch another Falcon 1 as early as next month.

Besides the Falcon 1, SpaceX is developing for NASA a larger launch vehicle, Falcon 9, capable of flying to the international space station when the current space shuttle fleet retires in 2010.