Dec. 5, 2016

— Virgin Galactic's second SpaceShipTwo, the VSS Unity, successfully completed its first free flight on Saturday (Dec. 3), touching down safely at the Mojave Air and Space Port in California.

The piloted test flight of the space tourism vehicle followed four captive carry tests, where VSS Unity flew attached to its WhiteKnightTwo mothership, VMS Eve. Saturday's free flight marked the 218th flight of the carrier aircraft.

"Mountains of data and analysis preceded this flight," said Virgin Galactic on Twitter after the flight was underway. "In testing, you check every assumption."

Click to enlarge and view video in a new window. (Virgin Galactic)

This glide test marked the beginning of a series of planned free flights intended to prove VSS Unity's performance in a variety of conditions; both heavy, simulating the full weight of a load of fuel, oxidizer, pilots and passengers, and light, with empty tanks, and in between, at a variety of flight path angles and airspeeds.

"Today, Unity is flying light," the company tweeted.

For this first test, Virgin Galactic kept the vehicle at a light weight and placed a "speed limit" on its pilots (Mach 0.6), according to a statement posted to the company's website.

"Once we analyze the results, we'll be cleared to go faster on subsequent tests," said the company.

Piloting Unity were Mark Stucky, a former NASA astronaut instructor and Air Force test pilot who has been with Virgin Galactic since 2008, and David Mackay, Virgin Galactic's chief pilot. Aboard VMS Eve were pilots Mike Masucci and Todd Ericsson, with flight test engineer Dustin Mosher.

VSS Unity separated from the Virgin Mothership Eve at 50,000 feet and then flew free for 10 minutes to a landing. (Virgin Galactic)

VSS Unity was in free flight from an altitude of 50,000 feet (15,240 m) for ten minutes. The entire test flight, from take off of WhiteKnightTwo to the touch down of SpaceShipTwo lasted one hour and 20 minutes.

VSS Unity is the first vehicle built by Virgin Galactic's sister organization, The Spaceship Company.

Virgin Galactic's first SpaceShipTwo, the "VSS Enterprise," was built by Scaled Composites. It flew 31 glide tests and three powered flights between 2010 and 2014. On Oct. 14, 2014, during its fourth engine test, VSS Enterprise broke apart, killing its co-pilot, Mike Alsbury, and severely injuring its pilot, Pete Siebold.

A National Transportation Safety Board investigation found that the accident had been the result of pilot error; Alsbury had unlocked the feather braking system early, causing its tail booms to rise as the craft accelerated through Mach 1.

The Spaceship Company redesigned the vehicle's controls so that the feather could not be prematurely deployed and restructured its test program to improve safety.

Virgin Spaceship Unity touches down after flying freely for the first time on Dec. 3, 2016 in the Mojave Desert. (Virgin Galactic)

"We have not yet reached the rocket powered phase of the test flight program," the company said on its website after Saturday's flight. "First we need to gather test flight data to confirm our analyses and calculations about how Unity will perform in a wide variety of real-world flight conditions."

An initial look at the data, as well as feedback from Stucky and Mackay, indicated that the flight went "extremely well," according to Virgin Galactic.

"We are looking forward to getting back into the skies," the company said, "as soon as the engineers say we're ready to do so."

Sir Richard Branson, Virgin Galactic's founder, and George Whitesides, the CEO of Virgin Galactic and The Spaceship Company, were on hand to greet and congratulate Stucky and Mackay after the flight.