Paul Allen’s Stratolaunch Systems lays out a roadmap for hypersonic rocket planes

Stratolaunch’s swept-wing hypersonic testbed would be propelled by a rocket engine. (Stratolaunch Illustration)

Stratolaunch Systems, the aerospace company created by Microsoft co-founder Paul Allen, says it’s exploring the development of a series of rocket planes that would serve as a testbed for hypersonic flight.

Stephen Corda, Stratolaunch’s senior technical fellow for hypersonics, presented the concept this week at the American Institute of Aeronautics and Astronautics’ International Space Planes and Hypersonic Systems and Technologies conference in Orlando, Fla.

If Stratolaunch follows through on the concept, the company could use the world’s largest airplane as a launch platform for an uncrewed aerospace plane that travels at more than 10 times the speed of sound, or Mach 10.

Hypersonic vehicles rank among the top technological frontiers for Pentagon officials, who have sounded the alarm about hypersonic weapon development programs in Russia and China. But it’s not yet clear whether Stratolaunch will join the hypersonic aerospace race.

“We are currently exploring potential partnership opportunities to develop an air-launched hypersonic testbed,” Stratolaunch said today in an emailed statement. “The hypersonic testbed would be deployed from our carrier aircraft and would be used for hypersonic research and technology development for space launch systems, however, no decision have been made yet.”

In the concept study presented this week, Corda and his colleagues provide a detailed description of a delta-wing testbed plane called the Hyper-Z. It would be 83.4 feet long, with a wingspan of 32.4 feet and a launch weight of about 65,000 pounds.

Stratolaunch’s hydrogen-fueled PGA rocket engine would serve as the plane’s main propulsion system, but it could also be equipped with an air-breathing propulsion system, such as a scramjet engine. The flight profiles could accommodate a maximum speed of Mach 11, or a maximum altitude of 477,000 feet.

Hyper-Z would be launched from Stratolaunch’s mammoth twin-fuselage carrier airplane, which has a record-setting wingspan of 385 feet. The plane is currently going through ground testing at California’s Mojave Air and Space Port and should have its maiden test flight within the next few months.

The testbed design could accommodate equipment related to hypersonics and space launch development, and external payloads could be mounted to its underbelly, Stratolaunch said.

Hyper-Z’s main mission would be to test the aerodynamics and technologies required for hypersonic flight — blazing the trail for a full line of rocket-powered vehicles including a crew-capable orbital space plane that Stratolaunch has dubbed “Black Ice.”

The design also allows for small payloads and experiments that could be placed at strategic locations on the vehicle, known as hyper-spots. “A goal of this concept is to make the hypersonic flight environment accessible to universities, small business and other smaller concerns,” Corda and his colleagues write.

To smooth the way for Hyper-Z, Stratolaunch proposes building a subscale version of the plane called Hyper-A. This precursor plane would be about 28 feet long, with a wingspan of 11 feet and a launch weight of 6,000 pounds. That would make Hyper-A just a bit bigger than the Air Force’s Boeing-built X-51 Waverider aircraft, which put in a record-setting hypersonic flight in 2013.

Hyper-A is designed to fly beyond Mach 6, well above the Mach 5 speed that generally defines hypersonic flight. Its flight profile could be tweaked to go as fast as Mach 7.7, or rise as high as 125,000 feet.

Stratolaunch has already conducted low-speed wind tunnel tests for the Hyper-Z design, and high-speed wind tunnel tests are to begin this fall. But because the project hasn’t yet gotten the full go-ahead, Stratolaunch hasn’t committed to a time frame for development.

The carrier airplane — which has been nicknamed “Roc” after the mythical giant bird in “A Thousand and One Nights” — is expected to require 18 to 24 months of flight testing before it’s cleared to launch payloads. That suggests the first flight of Hyper-A could take place no earlier than 2020.