Stratolaunch airplane in flight
Stratolaunch’s Roc carrier plane flies above California’s Mojave Desert. (Stratolaunch via Twitter)

Stratolaunch, the aerospace company founded by the late Seattle billionaire Paul Allen, put the world’s biggest airplane through its second flight test today, two years after the first flight.

“We are airborne!” Stratolaunch reported in a tweet.

Today’s takeoff from California’s Mojave Air and Space Port at 7:30 a.m. PT marked the first time the plane, nicknamed Roc after the giant bird of Arabian and Persian mythology, got off the ground since Stratolaunch’s acquisition by Cerberus Capital Management in October 2019. The flight was expected to last more than three hours — longer than the first flight on April 13, 2019.

Since then, the business model for the 10-year-old venture has shifted: In its early years, Stratolaunch focused on using Roc as a flying launch pad for sending rockets and their payloads to orbit. The concept capitalizes on the air launch system pioneered by SpaceShipOne, which won financial backing from Allen and won the $10 million Ansari X Prize in 2004,

The new owners still expect to use Roc for air launch, but the current focus is on using the plane as a testbed for Stratolaunch’s hypersonic flight vehicles, Once the plane is cleared for regular operations, perhaps next year, Stratolaunch could begin launching its Talon-A prototype hypersonic plane.

Hypersonic flight at five times the speed of sound is a big deal for military applications. Russia and China are said to be working on hypersonic weapons systems, and the U.S. military is keen to keep up. Stratolaunch’s technology could figure in the Pentagon’s plans.

Stratolaunch hasn’t ruled out eventually pursuing other applications for its air launch system, including sending payloads and crewed space planes into orbit.

Other companies, principally including Virgin Orbit, are also working on next-generation air launch technology. Such systems hold the promise of greater versatility and quicker response time for launching payloads, due to the fact that the carrier planes can take off from a wide variety of runways, fly around inclement weather and theoretically launch their payloads in any desired orbital inclination.

Stratolaunch’s twin-fuselage, six-engine Roc airplane is in a class by itself, thanks to its world-record wingspan of 385 feet. In comparison, the wingspan of the modified Boeing 747 that Virgin Orbit is using comes to 211 feet. The previous record-holder was the Spruce Goose, a prototype seaplane that made its debut in 1947 and had a 320-foot wingspan.

Built by Mojave-based Scaled Composites, Roc is built to carry more than 500,000 pounds of payload. During 2019’s test flight, the airplane reached a maximum speed of 189 mph and maximum altitude of 17,000 feet. Stratolaunch said today’s test would involve a series of aerial maneuvers, including low approaches, with details to be laid out during a post-landing news briefing at 1 p.m. PT.