Stratolaunch’s Roc—the biggest aeroplane in the world—completed its first test flight in more than eight months on Sunday (January 16).

The test flight, the third in the plane’s history was wheels up at 8:47 am on the 12,500-foot Runway 30 at California’s Mojave Air & Space Port. The four-hour-and-23-minute mission expanded Roc’s proven test envelope, including a higher altitude, as well as retracting and extending one of its main landing gear in flight for the first time. 

In addition to setting a Roc record for flight duration, the mission pushed its proven test envelope for altitude and speed. The behemoth reached a maximum altitude of 23,500 feet and a top speed of 180 knots of indicated airspeed (kias), Stratolaunch said, making it Roc’s most productive test flight so far.

During previous flights, the airplane climbed to about 17,000 feet and accelerated to 165 kias. Roc was designed to fly to altitudes around 35,000 feet, reaching a top speed of 500 keas.

Stratolaunch president and CEO, Zachary Krevor, said in a statement that, “today’s successful flight demonstrates and validates improvements to the carrier aircraft’s systems and overall flight performance.” The one-of-a-kind, six-engined, twin-fuselage jet is to serve as a carrier to air-launch reusable hypersonic aircraft for testing and research.

Events leading up to test flight

In the weeks leading up to this latest test flight crews practised taxi test runs, operating the airplane’s communications, airworthiness, and all of its subsystems to ensure proper functionality. Surprisingly, during the initial ascent, the winged behemoth packs some actual get-up-and-go.

During Roc’s historic first flight in April 2019, the flight crew discovered that the airplane gains altitude much more quickly than expected. Roc, built by Scaled Composites, founded by Burt Rutan, was designed as an in-flight launch platform. 

Originally, a key purpose for the airplane was to launch small satellites into low Earth orbit from the air but Roc’s mission changed after the tragic 2018 death of Stratolaunch founder, Paul Allen. After ownership of the company transitioned to Cerberus Capital Management, Roc’s focus shifted to launching hypersonic test vehicles. 

Plans for fourth test light underway

Engineers plan to use Roc to launch a hypersonic testbed vehicle called Talon, currently under development by Stratolaunch. Plans for a fourth flight test are already underway with engineers planning to install a pylon that will enable Roc to carry various launch vehicles.

Stratolaunch expects Roc to begin commercial operations later this year. It took more than eight months to resume flight testing due to the transition to new ownership as well as a “considerable amount” of developments made to the aircraft, including a command-by-wire system on Roc’s massive outboard ailerons and some adjustments to the leading edge of the enormous wings.