In a Dec. 11 statement, the company said the next powered test flight of VSS Unity, the second SpaceShipTwo, is planned for a window that opens Dec. 13 from the Mojave Air and Space Port in California. The flight would be the fourth powered flight for this vehicle and the first since July. The statement came shortly after the publication of airspace restrictions in the vicinity of the airport "for rocket launch and recovery" for Dec. 13 through 15.

"At a basic level, this flight will aim to fly higher and faster," the company said in its statement. "We plan to burn the rocket motor for longer than we ever have in flight before, but not to its full duration."

The flight will collect "new and important data points" about the vehicle at higher altitudes and speeds, including supersonic handling qualities and thermal dynamics. How well the vehicle is doing will determine how long they burn the rocket motor, the company stated. On the previous flight, SpaceShipTwo's hybrid rocket motor burned for 42 seconds, while a full-duration burn would run about one minute.

On that previous flight, SpaceShipTwo reached a peak altitude of 32 miles (52 kilometers), and the company suggested the vehicle could go much higher on the upcoming flight. "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," it stated.