On April 29, 2013, Virgin Galactic took a huge
step toward suborbital spaceflight -- the six-person SpaceShipTwo
ignited its rocket engine for the first time in flight, accelerating it
to supersonic speeds. Richard Branson called the test "critical." Seen
here, WhiteKnightTwo -- SpaceShipTwo's mothership -- taxis along the
airstrip at California's Mojave Air ans Space Port shortly before
takeoff at 7 a.m. PST.