Virgin Galactic has taken another step back into space with the first free flight of its VSS Unity spaceplane with its propulsion system installed. The sixth glide test of the passenger-carrying hypersonic craft was conducted over the Mojave Desert in California as a dry-run for future rocket powered tests that will propel briefly it on a suborbital trajectory into space.

The latest test flight took place on August 4 when VSS Unity was taken aloft by its mothership, VMS Eve, piloted by Nicola Pecile and Mike Masucci with flight test engineer Dustin Mosher. Meanwhile, VSS Unity was under the command of test pilots Dave Mackay and CJ Sturckow.

This was the first time the replacement prototype for the VSS Enterprise, which was lost in a midair accident in 2014, has flown with its propulsion system installed. This includes the centrally positioned Main Oxidizer Tank that was fully charged with nitrous oxide. The only thing missing was the solid propellant, called the Case-Throat-Nozzle, which was replaced by 1,000 lb (454 kg) of water ballast. In addition, the forward pressurant tank was filled with helium.

As part of the flight test, Mackay and Sturckow vented the nitrous tank while still attached to the mothership. At above 40,000 ft (12,200 m), the spaceplane was released and the twin tail booms raised into the feathered reentry configuration as the pilots evaluated how the extra weight of the propulsion system affected the center of gravity for flight and landing.

After the booms were returned to their original position, Unity was put through a high-g pull-up maneuver and bank-to-bank rolls before returning to the Mojave airstrip. The flight data will now go on to analysis.

"We are really pleased with what we saw today," said Chief pilot David Mackay. "We collected hundreds of gigabytes of data for us to review, and from the pilots' point of view, it felt really wonderful. All of you here at Virgin Galactic and The Spaceship Company should be very proud: VSS Unity is a great spaceship."

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