Twice in the past five months, the company launched a hypersonic vehicle over the Pacific Ocean, accelerated it to more than five times the speed of sound, and autonomously landed at Vandenberg Space Force Base in California. Stratolaunch used the same vehicle for both flights. This is the first time anyone in the United States has flown a reusable hypersonic rocket plane since the last flight of the X-15, the iconic rocket-powered aircraft that pushed the envelope of high-altitude, high-speed flight 60 years ago. He said the Talon test vehicle advances the capability lost with the retirement of the X-15 by flying autonomously. Like the Talon-A, the X-15 released from a carrier jet and ignited a rocket engine to soar into the uppermost layers of the atmosphere.