Updated Burt Rutan's SpaceShipOne is scheduled to blast off at 14.47 BST this afternoon for the first of its flights aimed at securing the $10m X-Prize.
The vehicle - which has already made one successful trip to 100km in June - will be carried to 47,000 feet by its White Knight mother ship and after release blast its way to the official boundary of space. If successful, it must complete the same feat within two weeks. The second shot is planned for 4 October.
SpaceShipOne is the product of Rutan's Scaled Composites, which is funded by Microsoft co-founder Paul Allen. Earlier this week, Brit entrepreneur Richard Branson ordered five scaled-up versions of the craft and is planning to bring space tourism within the reach of the common man - providing he is rather more than commonly endowed in the cash department. Flights are due to begin in 2007, and will set wannabe astronauts back £100,000.
This afternoon's lift-off is from Mojave, California. Reports say that thousands of eager spectators are descending on the town in anticipation of the event. The pilot for the flight has not been announced, but front-runner must be Mike Melvill, who piloted SpaceShipOne on its first sojourn into the stratosphere. Rutan himself is said to be keen to jump aboard the second flight. ®
SpaceShipOne finally blasted off at 14.11 GMT and landed safely back at Mojave around 90 minutes later - apparently having completed its mission with Mike Melvill at the controls. US television reports speak of "anomalies" during the flight - referring to the vehicle going into a spin shortly after separation from White Knight - but Melvill regained control and was able to take SpaceShipOne halfway to the $10m X-Prize.
Virgin to offer space flights
Cheap rocket crumbles in hunt for $10m space prize
Rutan bagsies 'shotgun' in SpaceShipOne
X-prize race hots up
US edges closer to private space flight
FAA greenlights private spaceship