SpaceCon one is the moment for last minute preparations.
Virgin Galactic’s technicians fuss over spaceship Unity inside her vast hangar, tightening insulating panels and topping up the tanks of compressed oxygen that will be used for in-flight navigation. She is already slung beneath White Knight, the four-engine aircraft that in the next few hours will carry her into the sky.
From there, her two pilots will fire the giant rocket engine accelerating the craft to speeds of more than Mach 3 and into space for the first time.
It is the next major milestone in Richard Branson’s plan to take paying customers into space and to be the first to do so without government help.
In the hours before launch, George Whitesides, the chief executive of Virgin Galactic, exudes a mix of nerves and excitement as he stands before the rocket ship at the company’s spaceport in the Mojave Desert, California.
Little grows here apart from wind turbines and solar farms.
The spaceport itself grew out of a dusty naval base. One corner is given over to the boneyard, where dozens of decomissioned airliners lie yellowing in the sun.
The two main runways are surrounded by a complex of hangars and office buildings, taken over by space startups.
Close up, Unity is a simple beast. One giant engine fused into a wing.
"All it needs is a bunch of nitrous oxide and a couple of pilots to fly it," said Mr Whitesides, as for the first time he offered visitors, including The National, a glimpse of the spacecraft's final preparations before take-off.
Reaching beyond the threshold of space would represent critical progress towards commercial flights that were promised a decade ago.
It would catapult the company, which is backed by Abu Dhabi’s Aabar Investments, into poll position among the pioneers racing to take customers into space. And it would demonstrate that Virgin Galactic had overcome the tragic setback of an explosion during its 2014 test flight, in which a co-pilot was killed.
More than 600 people from more than 50 countries have already paid $250,000 to reserve seats in the six-passenger rocket craft, which is about the size of an executive jet.
The window for its test launch – when climatic conditions are just right – opens at 7am local time on Thursday and extends for three days.
If all goes to plan, Unity will climb more than 50 miles above the earth’s surface and into space where the pilots will experience micro-gravity. Some aviation agencies have different definitions of exactly where the earth’s atmosphere ends and space begins but Nasa and the US Air Force award astronaut wings at an altitude of 50 miles and beyond.
If the spaceship’s sensors indicate abnormal stresses or if the pilots are unhappy with the conditions, they may decide not to fire their engine for the full 50-plus seconds necessary.
“This is test flight,” said Mr Whitesides in a briefing to observers, as Mr Branson brewed tea nearby. “You are going to be watching a no-kidding test flight, with all of the novelty and excitement that goes along with a real test flight.
“Risk is a valuable part of forward progress. And intrinsic in risk is that sometimes you have good days and sometimes you have bad days.”
For the two test pilots that day will be begin at 5.30am, when they strap themselves into a flight simulator tucked behind curtains in one corner of the vast hangar. The computer will be programmed with the latest air speeds and temperatures.
White Knight will then take off from Mojave Air and Space Port, climbing into the sky until it reaches an altitude of 43,000 feet.
At that point, Unity is released from her cradle, testing her pilots to their limits. For three seconds she falls, allowing the carrier to climb away before the order is given: “Rocket motor ignition.”
Within moments, she accelerates to supersonic speeds. After 10 seconds, the pilots throw her into a carving “gamma turn”, hitting an almost vertical climb, accelerating past Mach 2 and beyond Mach 3.
She keeps climbing even after the pilots cut the solid-fuel rocket at some point after 50 seconds of burn. Then she arrives in space before the earth’s gravity slows her to a stall and pulls her back down.
The descent involves a unique “feathering” configuration in which the twin tails rotate upwards, increasing drag and stabilising the craft before its final glide mode, landing like a conventional aircraft on a runway.
In all, the flight is expected to last about 20 minutes, generating reams of data that technicians will use to push the next test even further and even higher.
“Whether we complete all our objectives during the next flight or need to wait a little longer, we remain committed to completing the final stages of this extraordinary flight test program as quickly, but more importantly as safely, as possible,” said the company in a statement.
The quest began in 2004 when Mr Branson founded Virgin Galactic after the success of SpaceShipOne, the first privately financed manned spacecraft that made three trips into space.
Today, he faces competition from fellow billionaires Jeff Bezos, the Amazon chief executive, and Elon Musk, SpaceX founder, to be the first to carry paying tourists into space.
Virgin will be a step closer if it succeeds in pulling off the first manned flight into space since the Nasa shuttle programme ended.
Todd Ericson, a test pilot and vice-president of safety, says all that stands in the way of that feat are weather conditions and the approval of the two test pilots before White Knight blasts them and their Unity spaceship into the sky.
“They just need to be happy with the way it’s going to go on the day.”