The mammoth airplane that got its start with backing from the late Seattle billionaire Paul Allen took to the air today for its third test flight — marking a new chapter in Stratolaunch’s decade-long effort to create a flying launch pad.
Stratolaunch’s twin-fuselage, six-engine Roc aircraft, named after a mythical giant bird, is the world’s largest airplane by wingspan. Its 385-foot spread is more than half again as wide as the wings of a Boeing 747.
When Allen founded Stratolaunch back in 2011, his intention was to use Roc to send rockets into orbit from the air. But after Allen’s death in 2018, the company was transferred to new owners — and Roc’s primary purpose pivoted to launching hypersonic test vehicles for military and commercial research.
If the development program proceeds as planned, Stratolaunch could begin testing its air-launched, rocket-powered Talon-A hypersonic vehicle as early as this year.
Today’s flight was conducted from California’s Mojave Air and Space Port and lasted four hours and 23 minutes. It came nearly three years after Roc’s first aerlal test, and almost a year after the second flight. The outing’s main objective was to evaluate the airplane’s performance and handling characteristics at increased altitude, and to retract and extend the left mid-main landing gear.
Stratolaunch said Roc reached an altitude of 23,500 feet at an indicated air speed of 180 knots (207 mph), besting the previous flight test’s maximum altitude of 14,000 feet. Before landing, the plane’s crew conducted a couple of close approaches for testing purposes.
“Today’s successful flight demonstrates and validates improvements to the carrier aircraft’s systems and overall flight performance,” Zachary Krevor, Stratolaunch’s president and chief operating officer, said in a news release. “We will take the data we gathered today and continue to advance the aircraft’s operational performance to support hypersonic testing in 2022.”
Krevor said today’s partial gear retraction was part of Stratolaunch’s “graduated approach to building confidence in the landing gear and gear door hardware.”
“Testing the left main landing gear individually mitigated risk and provided our aircrew with options for landing the aircraft in the event the hardware didn’t perform as expected,” he said. “We’ll review the data and determine when we can get back into the air to continue advancing our unique, hypersonic architecture.”
The plane was flown by senior test pilot Mark Giddings, with Evan Thomas serving as co-pilot. Thomas is Stratolaunch’s director of flight operations and piloted Roc’s first two test flights. Jake Riley was onboard today as the crew’s flight engineer.
During a webcast presented by NASASpaceflight.com, Stratolaunch design engineer Grace Wang said six to eight flight tests were planned in preparation for operational hypersonic launches. Stratolaunch’s chief technology officer, Daniel Millman, said during a post-landing teleconference that the next test flight would expand the envelope for landing-gear operation, and that the pylon for the Talon-A hypersonic test vehicles would be installed for the fifth test flight.
The first two Talon-A vehicles, known as TA-0 and TA-1, are under development. Stratolaunch said TA-1 completed its initial power-on testing in late December.
Hypersonic flight has become a national security priority in recent years, in part due to efforts by Russia and China to develop hypersonic weapons that could elude U.S. defenses. Stratolaunch has won a contract from the Missile Defense Agency to assess how reusable hypersonic testbeds could be used for defense applications.
Stratolaunch argues that its air-launch system is more versatile than a fixed-site launch system because it can operate from any airport with a runway big enough to accommodate Roc (such as Mojave’s 12,500-foot runway), can dodge inclement weather, and can deploy launch vehicles in any desired inclination.
The air-launch approach, which was used successfully for the Allen-backed SpaceShipOne project in 2004, has also been adopted for Virgin Galactic’s SpaceShipTwo rocket plane and Virgin Orbit’s Launcher One system.
Update for 4:15 p.m. PT Jan. 16: We’ve revised this report to reflect more precise flight statistics and updated quotes from Stratolaunch’s Zachary Krevor and Daniel Millman.