Virgin Galactic's commercial passenger-carrying craft the SpaceShipTwo has just passed a critical milestone: In a test flight it's just fired up its engine—and broken the sound barrier—for the first time.
Virgin Galactic's Twitter account provided the up-to-date news on the test flight, reporting that at around 10:50 Eastern Time:
For the 1st time ever, SS2 has lit her rocket engine in flight! A major milestone in human spaceflight. Photos, video, and details to follow— Virgin Galactic (@virgingalactic) April 29, 2013
The craft was also confirmed as breaking the sound barrier by pilots Stucky and Alsbury. The engine burned for just 16 seconds, but that was enough to propel it from its launch height of 47,000 feet to over 55,000 feet and a top speed of Mach 1.2 (for context your average airliner flies at about 35,000 feet and Mach 0.8, and even Concorde only flew at Mach 2.02 and a cruising height of about 56,000 feet).
This flight marks one of the few remaining test barriers to actually flying the vehicle into space, and then finally to carrying passengers above the atmosphere in what's called a suborbital "pop-gun" flight (like Alan Shepard's historic trip on May 5th 1961). Virgin Galactic's effort is based on proven technology developed to beat the first X-Prize competition, and is very different from other commercial space efforts like SpaceX's.