16 kilometers, or 52,000 ft, underneath a carrier aircraft, White Knight II, after separation the vehicle would continue to over 100 km (the Kármán line, a common definition of where "space" begins). The time from liftoff of the White Knight booster carrying SpaceShipTwo until the touchdown of the spacecraft after the suborbital flight would be about 2.5 hours. The suborbital flight itself would be only a small fraction of that time, with weightlessness lasting approximately 6 minutes. Passengers will be able to release themselves from their seats during these six minutes and float around the cabin. Development operations 2007 Scaled Composites fuel tank testing explosion In July 2007, three Scaled Composite employees were killed and three critically injured at the Mojave spaceport while testing components of the rocket motor for SpaceShipTwo. An explosion occurred during a cold fire test, which involved nitrous oxide flowing through fuel injectors. The procedure had been expected to be safe. Commencement of sub-space test flights Just a year later, in July 2008, Richard Branson predicted the maiden space voyage would take place within 18 months. In October 2009, Virgin Galactic announced that initial flights would take place from Spaceport America "within two years." Later that year, Scaled Composite announced that White Knight Two's first SpaceShipTwo captive flights would be in early 2010. Both aircraft did fly together in March 2010. The credibility of the earlier promises of launch dates by Virgin Galactic were brought into question in October 2014 by its chief executive, George Whitesides, when he told The Guardian: "We’ve changed dramatically as a company. When I joined in 2010 we were mostly a marketing organisation. Right now we can design, build, test and fly a rocket motor all by ourselves and all in Mojave, which I don’t think is done anywhere else on the planet". On 7 December 2009, SpaceShipTwo was unveiled at the Mojave Spaceport. Branson told the 300 people attending, each of whom had booked rides at $200,000 each, that flights would begin "in 2011". However, in April 2011, Branson announced further delays, saying "I hope 18 months from now, we’ll be sitting in our spaceship and heading off into space". By February 2012, SpaceShipTwo had completed 15 test flights attached to White Knight Two, and an additional 16 glide tests, the last of which took place in September 2011. A rocket-powered test flight of SpaceShipTwo took place on 29 April