By Irene Mona Klotz
in Mojave, California
The idea of launching into space from mid-air was not invented by Burt Rutan and his team at Scaled Composites.
White Knight and SpaceShipOne: The concept is not a new one
The basic plan was developed and tested four decades ago by a US government programme known as the X-15.
Neil Armstrong, the first person to walk on the Moon, cut his teeth not in a Gemini or Apollo capsule, but in the cockpit of an X-15 hypersonic aircraft.
But Nasa opted for rocket technology based on ballistic missile design, a decision that has led to labour-intensive, expensive transit systems.
Rutan aims to change all that with SpaceShipOne, a reusable suborbital vehicle designed to take three people to the edge of space.
Safe and easy
"I took risks on this programme I didn't have to take," said Rutan, an award-winning designer whose creations include the Voyager aircraft that flew around the world non-stop and without refuelling.
Among the innovations nestled within SpaceShipOne's sleek form is an atmospheric re-entry system that is impervious to the vehicle's direction during the critical, high-temperature descent back to Earth.
The wings are tucked up for re-entry
"We can enter in any direction," Rutan said. "We have a spaceship that does not have to be controlled upon re-entry and that is an enormous safety factor."
Like the X-15, SpaceShipOne will be carried to its launch altitude by another vehicle, in this case a twin-engine turbojet named White Knight.
When the vehicles reach about 15km (50,000ft), SpaceShipOne will be released from beneath White Knight for a hypersonic climb into space.
Pilot Mike Melvill will orient SpaceShipOne's nose straight up while the craft free-falls for up to 15 seconds. Then he must flip and switch and ignite his spaceship's innovative hybrid rocket motor, which was custom-built for Rutan by SpaceDev of San Diego.
The motor burns a solid rubber propellant with liquid nitrous oxide - a liquid version of "laughing gas".
The X-15: A pacesetter back in the 60s
If all goes as planned, SpaceShipOne's engine will burn for 80 seconds, then coast up to 100km (62 miles) - the official altitude of space.
If Melvill encounters any problems during flight, he can shut down the engine by cutting off the flow of nitrous oxide.
If successful, the ship will set a new speed record for a private aircraft - Mach 3.2 - and Melvill will get to see the curvature of Earth set against the blackness of space as well as experience about three-and-a-half minutes of weightlessness.
To prepare for re-entering the atmosphere, Melvill will rotate SpaceShipOne's wings vertically in respect to the fuselage, a manoeuvre known as "feathering".
The position increases the atmospheric drag on the vehicle so that it automatically orients itself to minimize friction and heating during re-entry.
When the vehicle falls to about 18km (60,000ft), Melvill will pivot the wings back down and glide to a runway at the Mojave Airport. The coast home takes about 15 minutes.
SpaceShipOne was financed by Microsoft co-founder Paul Allen, who said he spent more than $20m on the project.
Rutan said: "We built a complete manned programme from scratch for the price of one of those government studies."