Virgin Galactic said its space tourism rocket plane could reach “space altitudes” for the first time as early as Thursday.

The company said its SpaceShipTwo, VSS Unity, has entered the next stage of testing which will “expand the envelope for altitude, air speed, loads and thermal heating”.

The rocket motor on the spaceship will burn for a longer period on the next flight, which is set to take the pilot and aircraft into space for the first time.

Virgin Galactic, founded by billionaire businessman Richard Branson, said the window for the next phase will begin on Thursday but the nature of flight testing means it may take longer to get to the milestone.

If this test flight in Mojave, California is successful, the two pilots on board will experience an extended period of micro-gravity but “will be strapped in throughout”.

As well as the higher altitudes, the company said they will also look to simulate the commercial weight distribution on the test flight in preparation for future passengers.

‘Higher and faster’

A spokesman for Virgin Galactic said: “Our window for our fourth powered test flight opens on 13 December 2018. At a basic level, this flight will aim to fly higher and faster. We plan to burn the rocket motor for longer than we ever have in flight before, but not to its full duration.

“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 programme as quickly, but more importantly, as safely as possible.”

More than 600 people from 50 countries have reserved places to fly with Virgin Galactic when all testing has been completed.