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Countdown to historic space trip
SpaceShipOne, the first private manned spacecraft, is undergoing final preparations before its historic flight to the edge of space on Monday.
The craft, built by aviation pioneer Burt Rutan, will be launched into the sky by its carrier, White Knight, then rocket upwards to 100km (62 miles).
No private craft has ever been so high. In May, it reached 64km (40 miles) in a test flight, doubling its last best.
The attempt over California's Mojave Desert is due to launch at 1330 GMT.
Mr Rutan and his team from his company, Scaled Composites, hope the flight will take them closer to winning the Ansari X-prize of $10m (£5.7m) awarded to the first non-government, manned flight into space.
Windy concern
The as yet unnamed pilot will also rocket into the record books to become the first civilian to fly a spaceship out of Earth's atmosphere.
The pilot's name will be confirmed on Sunday. May's test flight was piloted by Mike Melvill.
If the mission is a success, SpaceShipOne will attempt the X-prize at a later stage.
To beat 25 other teams to the X-prize, SpaceShipOne must reach 100km - space's official boundary - twice in two weeks with a crew of three.
When the X-prize is claimed, it could open up the skies to future tourist trips to the edge of space for those bored of the usual beach holiday.
Monday's historic flight is being attempted early in the day (0630 PDT) because it is less likely to be very windy at that time and a lower Sun angle affords a better view.
High winds or cloudy skies could jeopardise the flight plans.
But BBC weatherman Rob McElwee told BBC News Online that the weather should be on the side of SpaceShipOne over the Mojave Desert.
Rocket burn
"On Monday morning, the pressure gradient will be loose," he explained. "That means relatively light winds, and in this case, from the surface to the tropopause.
"At launch height, it should be no more than 10 knots. But there is a possibility of a katabatic wind off the high ground. That may give a gusty surface wind around dawn."
A katabatic wind is a cool one that blows down a hillside. This is because the air at the top cools more quickly at night then sinks because it is denser.
If the weather does behave, Monday's flight will see White Knight lift off from the runway in front of gathered crowds. SpaceShipOne will be carried by the craft to an altitude of 50,000ft (15km).
That should take an hour, after which SpaceShipOne will be unleashed into the skies.
It will glide very briefly before firing up its rocket for about 80 seconds. It will blast off to its target height of 100km in a vertical climb at Mach 3 (three times the speed of sound).
When it has reached its target altitude, the vehicle will change its wing configuration to allow for high drag, and will start to fall back towards Earth during which the pilot will be weightless.
At re-entry, the ship's special wing configuration will allow it to glide back down to Earth in about 20 minutes.
Back for more
The craft will escape Earth's atmosphere, but it will not be able to orbit the planet because of the speed it is going.
Going sub-orbital is cheaper and far less riskier, but it still means the pilot will have a stunning view of Earth.
Burt Rutan has been widely acclaimed for his pioneering achievements in the field of aviation.
White Knight and SpaceShipOne are thought to be revolutionary in many ways. SpaceShipOne's hybrid engines need special fuel that is safer, and both White Knight and the ship can be reused.
The fuel used, specially developed by US firm SpaceDev, is called hydroxy-terminated polybutadiene (HTPB). It is a mix of rubber and nitrous oxide, commonly known as laughing gas.
It is not volatile and it is more eco-friendly than other space rocket fuels. Its by-products are water vapour, carbon dioxide, carbon monoxide and nitrogen.
The conventional space shuttle's solid rocket boosters burn ammonium perchlorate and aluminium.
Story from BBC NEWS:
SPACE FLIGHT ATTEMPT
SpaceShipOne boosts itself into the atmosphere
It aims for an altitude of 100km (62 miles)
Wings fold up to provide "feather" effect
Converts back to non-feathered glider