Virgin Galactic is hoping to "reach space for the first time" on Thursday as it sends its SpaceShipTwo vehicle on a test flight it hopes could pave the way for commercial space travel.
The test flight is scheduled to depart from Mojave, California at 1000 Eastern Time (1600 CET) on Thursday.
"At the basic level, this flight will aim to fly higher and faster, " the company said in a statement.
It added: "We also plan to burn the rocket motor for durations which will see our pilots and spaceship reach space for the first time."
250,000 US dollars
Virgin Galactic was founded by British billionaire Richard Branson in 2004 in the hope of becoming the first company to send paying customers to space.
More than 600 people from around the world have already paid for tickets, according to the statement. Tickets cost $250,000 (€220,000).
Branson had initially said that the company could start sending people into space from as early as 2007 but the deadline has repeatedly been postponed due to technical difficulties.
One pilot lost his life and another was seriously injured in 2014 after the SpaceShipTwo crashed during a test flight. An investigation found that human error — the braking system was triggered too early — and inadequate safety measures were to blame.
But in October, Branson told CNBC that he could be in space "in months and not years."
How it works
The SpaceShipTwo vehicle is not launched, it is instead carried to about 14,000 metres by a special plane, the Virgin Mothership —nicknamed VMS Eve after Branson's mother.
It then detaches, fires up its engine and climbs.
The goal is for the vehicle to reach an altitude of at least 50 miles (80 kilometres). NASA and the US define anyone who flies at this altitude as an astronaut.
"If all goes to plan our pilots will experience an extended period of micro-gravity as VSS Unity coasts to apogee," Virgin Galactic said.
The pilots should also "have some pretty spectacular views."
However it will fall short of crossing the Karman line, which at 100 kilometres high, represents the boundary between Earth's atmosphere and space.
According to the statement, if the flight is successful the company will then "start simulating the commercial weight distribution in the spaceship represented by our future passengers."
"Excitingly, we are partly achieving that on the next flight by carrying four research payloads that are part of the NASA Flight Opportunities Program."
Virgin Galactic is racing against other companies to send clients to space. Competitors include Blue Origin — founded by Amazon CEO Jeff Bezos — and Elon Musk's SpaceX whose unmanned Falcon 9 rocket has brought supply to the International Space Station for NASA.