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Virgin Galactic SpaceShipTwo VSS Unity
A long contrail extends behind Virgin Galactic’s VSS Unity rocket plane as it releases about 1,000 pounds of water from a ballast tank. (Virgin Galactic Photo)

Virgin Galactic’s SpaceShipTwo rocket plane took another step toward lighting up its engine in flight today, by simulating the shift in its weight with water instead of rocket fuel.

Today’s test flight involved sending up the plane, christened VSS Unity, from California’s Mojave Air and Space Port attached to its twin-fuselage White Knight carrier airplane.

Once the paired aircraft reached the proper altitude, White Knight Two released VSS Unity for an unpowered, gliding descent back to base. That’s been done four times before since last December, but this time, there was an added twist: Before takeoff, about 1,000 pounds of water were loaded into a ballast tank in the back of Unity’s fuselage.

The water, a stand-in for the fuel that will be consumed in Unity’s hybrid rocket engine, was dumped during the glide.

“That enabled us to explore the flight conditions we will experience during rocket-powered flights,” Virgin Galactic said in today’s post-flight update. “By jettisoning the water ballast on descent, we were also able to confirm handling characteristics as the vehicle’s center of gravity moved forward. Unity completed the flight with a safe and smooth landing in its lighter-weight configuration.”

Unity was piloted by Virgin Galactic’s David Mackay and CJ Sturckow. White Knight Two had Kelly Latimer and Michael Masucci at the controls, with Colin Bennett serving as flight test engineer.

Virgin Galactic said Unity is moving “towards the end of the initial glide test portion of the program” and heading toward its first rocket-powered tests. Eventually, test pilots will take the craft to outer-space heights, blazing a trail for suborbital space tourism.

About 700 customers have already paid as much as $250,000 for a seat on SpaceShipTwo, which is expected to go into commercial service within a year or two at Spaceport America in New Mexico. The precise timing depends on how the test program turns out. Virgin Galactic’s billionaire founder, Richard Branson, is likely to be among the first fliers.

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