On Wednesday, Stratolaunch’s Roc flew for the fifth time from California’s Mojave Air and Space Port (KMHV), bringing the Pentagon closer to new hypersonic test flights.
The Roc is the world’s largest plane by wingspan, and it’s designed to transport and launch the company’s rocket-powered Talon-A hypersonic vehicles for military and commercial usage.
At roughly 7:40 a.m. PT, Roc’s six Pratt & Whitney PW4056 turbofans and 385-foot wings lifted the 500,000-pound twin-fuselage jet above Runway 30. After nearly five hours of testing, the plane returned to KMHV at 12:37 p.m. PT.
Pilots Evan Thomas, Steve Rainey, and Jake Riley flew Roc with a 15-foot-by-15-foot pylon slung from the jet’s 95-foot centre wing for the first time, testing the device and several other onboard technologies. The crew retracted and extended Roc’s eight landing gear as a Cessna 550 Citation Bravo chase plane neared. The 8,000-pound pylon, though, received the most attention.
“It’s exciting to have the pylon on now,” Stratolaunch chief engineer Scott Schultz said.
“I’m excited about the pylon and the fact that we’re turning it into a flying launchpad.”
The role of the pylon cannot be emphasized enough. It is the core of Stratolaunch’s business strategy to launch small, autonomous, rocket-powered hypersonic testbeds from altitudes of roughly 35,000 feet. Roc’s business model crumbles in the absence of a pylon.
Talon-A is a testbed for Mach 6 that can be reused. A Talon-A separation test article is planned to be installed on Roc’s pylon for a separation test later this year. The pylon also houses updated Talon-A data collecting equipment and sensors.
Engineers will analyze data from Wednesday’s flight to determine how Roc flew with the pylon, including any detrimental flying characteristics.
“So one of the things we’re looking at is how this pylon affects the airplane as a whole,” Schultz explained. “How much rudder per beta? How much elevator per alpha? Are we on predictions from an alpha versus CL [lift coefficient] curve, which is how much lift the airplane makes with the angle of attack.”
“We’ve also got a significant amount of accelerometers on this pylon and throughout the airplane to measure buffeting coming off of the pylon that would shake the rest of the airplane,” Schultz said.
The pylon is constructed of metal with a carbon skin and will not be the final iteration.
“It’s designed for a very light launch vehicle like Talon, but we’ve baked in substantially more weight capability and margin than Talon—although it’s not quite a half-million-pound rocket structure yet,” he added.
Stratolaunch is planned to boost the frequency of its operations for Roc test flights. For example, Roc has flown in January, February, and now May of this year. This pattern is likely to expand in the future.
Stratolaunch CTO Daniel Millman urges the Pentagon to investigate flight testing technologies on low-cost testbeds that are “regular, routine, and reusable” as the Pentagon works to create hypersonic weapons.
Although Roc isn’t expected to fly until mid-to late-2023, Stratolaunch has a hypersonic research contract with the US Air Force Research Laboratory.
Furthermore, the company has agreed to supply “threat replication” to the Pentagon’s Missile Defense Agency to help scientists better understand how to engage and intercept hypersonic threats. Last month, Stratolaunch opened a permanent office in the Washington, D.C., region to help with future contracting.