The window for Virgin Galactic's fourth test flight opens Thursday, and the company is hoping its sleek VSS Unity spaceplane will get to the edge of space for the first time.
"At a basic level, this flight will aim to fly higher and faster," the company said in a statement.
Virgin Galactic also plans to "start simulating the commercial weight distribution in the spaceship represented by our future passengers," the company said.
Company founder Richard Branson had promised to start taking tourists — about 800 people have paid $250,000 for tickets — to the edge of space by the end of the year. But this test flight over California's Mojave Desert will carry only a pilot and co-pilot, according to Virgin Galactic.
"We plan to burn the rocket motor for longer than we ever have in flight before, but not to its full duration. At the end stages of the rocket burn in the thin air of the mesosphere and with the speeds that we expect to achieve, additional altitude is added rapidly," the company stated. "That results in new and important data points."
The goal is to get to the Kármán line, which marks the boundary between the upper atmosphere and outer space, where future space tourists will get to look back and earth and experience weightlessness.
"If all goes to plan our pilots will experience an extended period of micro-gravity as SpaceShipTwo coasts to apogee, although they will remain securely strapped in throughout," Virgin Galactic said. "They should also have some pretty spectacular views which we look forward to sharing as soon as possible post flight."
In July, during its third test flight, the spaceplane reached an altitude of 170,800 feet (32.3 miles), more than halfway to the goal of reaching the edge of space.
Elon Musk's SpaceX and Jeff Bezos's Blue Origin also intend to take space tourists up on brief suborbital flights for a substantial fee.
It's not clear if VSS Unity, which is normally launched from mothership WhiteKnightTwo, will be ready in time to hit Branson's goal of carrying paid customers by the end of December.
It wouldn't be the first time the entrepreneur got ahead of himself. After establishing Virgin Galactic in 2004 he said it would be ready for passengers by 2007.
This time around the company is at least hedging its bets.
"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," Virgin Galactic said in a statement.