Cracking the code of hypersonic flight: A decade of BOLT breakthroughs

From the heartbreak of an early flight failure to a resounding triumph over the Norwegian Sea, the Boundary Layer Transition and Turbulence (BOLT) Program spent nearly a decade launching rockets into the atmosphere, to investigate boundary layer transition and turbulence, key phenomena in hypersonic flight.

Boundary-layer transition may sound like a niche science term, but it has been the stubborn gatekeeper of ultra-fast flight for decades.

It dictates whether a vehicle glides smoothly through the atmosphere or fights a losing battle against a blowtorch of hot airflow capable of melting it.

Pinpointing exactly how and when this transition happens changes everything: lighter vehicles, optimized heat protection systems, longer flight ranges and unprecedented stability at speeds several times faster than the speed of sound.

Engineers long knew this transition mattered. What they needed were more, direct, real-world measurements of how it unfolds outside the lab, in the sky.

BOLT helped change that.

Born from the vision and leadership of Dr. Ivett A. Leyva — Texas A&M Fort-Worth associate dean for research and Arthur McFarland professor of aerospace engineering at Texas A&M University — during her tenure as a program officer at the Air Force Office of Scientific Research (AFOSR), BOLT would unfold into a saga of three flight experiments over the next decade.

While the first and third flight experiments were led by Johns Hopkins University Applied Physics Laboratory (APL), and the second by Texas A&M University, BOLT drew on broad support and expertise from a wide range of partners.

With AFOSR as the lead government sponsoring agency, the teams also included NASA Langley, Johnson and Wallops, University of Minnesota, Purdue University, CUBRC, VirtusAero, the German Aerospace Center (DLR), the Australian Defense Science and Technology Group, the University of Queensland, the Air Force Research Laboratory’s Propulsion Directorate and the University of Arizona.

The mission of this international coalition: to crack the code of boundary layer transition and turbulence.

"I created the program to energize the scientific community and challenge it to predict the boundary layer behavior of a new canonical geometry. Almost a decade later, the sky is recognized as the ultimate laboratory where hypersonic flow basic science experiments should also be done," Leyva said. 

The BOLT program’s journey and groundbreaking outcomes were presented in a recent proceeding, published at the AIAA SCITECH 2026 Forum.

When smooth air turns turbulent

At hypersonic-level speeds — at least five times faster than the speed of sound — air doesn’t just slip past a vehicle’s surface; it becomes an energy-packed heat envelope that clings to the vehicle’s shell.

“Air compresses, heats, ionizes and transfers energy to the vehicle’s skin through a thin region called the boundary-layer,” Leyva said.

Under the right conditions, this thin, normally smooth layer of air can erupt into violent, chaotic turbulence.

“Tiny wind instabilities can grow and trigger the path to turbulence,” Leyva said. “What generally begins as smooth flow can become chaotic. That’s the idea behind boundary-layer transition.”

For decades, this shift from uniform (laminar) to violent (turbulent) flow has been one of the least understood phenomena in hypersonic science and fluid mechanics.

“There was a real gap between the data produced in controlled settings and what actually happens during flights and in the sky,” Leyva said.

Cracking the code of hypersonic flight

To close that gap, BOLT scientists took their research from intricate computer simulations and confined labs into the open sky, capturing real-world, rare, high-quality data.

Among BOLT’s most significant achievements was linking elegant mathematical theories with practical engineering needs.

Engineers can fine-tune next generation hypersonic vehicles for lighter weight, improved heat protection, extended flight ranges and more efficient, stable flights.

The captured flight data also gives flight models, wind tunnels and computer simulations a tangible backbone to better predict — not just suggest — the effects of boundary-layer transition on hypersonic vehicles.

“As researchers develop new ways to predict transition and turbulence behaviors, they now have flight datasets to test against,” Leyva said. “We’ve grounded old simulation models with real flight data and are paving the way for new computational innovations.”

Ultimately, it is almost inevitable for a hypersonic vehicle to cross the same transitional frontier — but now, scientists and researchers have clear data to map out boundary-layer transition and turbulence behaviors for a broader set of conditions.

The BOLT saga: A tale of three flight experiments

Building on the strong legacy of the HIFiRE flight experiments developed by the Air Force Research Laboratory and AFOSR, BOLT was conceived in 2017 to test — even challenge — decades of assumptions about boundary-layer transitions and turbulence.

The journey started with BOLT-1A, led by APL’s Dr. Brad Wheaton.

After years of preparation, wind tunnel testing and high accuracy computations, BOLT-1A was a sobering reminder of the challenges of hypersonic flight. Shortly after a successful launch in Sweden, the rocket spiraled like a football due to flight instability.

“By identifying and modeling that anomaly with our partners, we were able to refine the experiment designs to enable subsequent flights and new, high-quality data for the research community,” Wheaton said.

BOLT-1A marked an early turning point for the team.

“While a setback, BOLT-1A wasn’t a failure,” Leyva said. “It provided us with invaluable ground testing and ever-more accurate numerical simulations as well as lessons on flight operations.”

Those lessons shaped the second flight experiment, BOLT II in memory of Mike Holden.

Led by Texas A&M’s Dr. Rodney Bowersox, the flight experiment — outfitted with more than 400 sensors along the rocket — revealed how both smooth surfaces and surfaces with tiny bumps can develop turbulent flow.

“The successful BOLT II flight in March 2022 didn’t just capture data, it tested decades-old theories of turbulence, distilled into real-world science,” Leyva said.

Finally, in September 2024, the team led by APL’s Wheaton returned to the skies over Norway with BOLT-1B, a repeat of BOLT-1A. But this time, the flight was a resounding success.

“It collected hundreds of high-fidelity measurements that revealed the physics and behavior of boundary-layer transition for the BOLT geometry,” Leyva said. “It was an amazing research achievement.”

After almost a decade of daring flights, setbacks and triumphs, BOLT proved that groundbreaking science thrives on collaboration, not isolation.

The collaborative engine behind a decade of hypersonic research

BOLT’s success wasn’t just through high-speed rockets; it was powered by a multidisciplinary research engine.

Universities, government agencies, international partners and private industry pooled expertise and resources to tackle fundamental science questions whose answers ripple and feed into practical hypersonic flight.

“Collaboration gave us access to perspectives and expertise we would have otherwise not developed independently,” Leyva said.

Equally important was training the next generation of scientists to carry the mantle and take the next leap in high-speed flight forward.

“Students were designing experiments, testing and analyzing real flight data and playing a central role in the program’s success,” Leyva said.

The near decade-long collaboration did more than capture first-of-its-kind science, it created a community.

“It wasn’t just about building rockets and testing them,” Leyva said. “It was about building relationships, people and skills that defined this decade, and will train the engineers for the next decade of hypersonic science.”

While the rockets reached Mach speeds far above 5, the BOLT program proved that the most powerful engine is human innovation: curiosity, teamwork and the courage to explore the unknown.

More information: Bradley M. Wheaton, Ivett Leyva, Rodney Bowersox, Graham V. Candler, Scott Berry, Aaron Dufrene and Sarah Popkin. “The BOLT Experiments: Outcomes from a Decade of Fundamental Science in Hypersonic Flight,” AIAA 2026-0957. AIAA SCITECH 2026 Forum. January 2026.

DOI: 10.2514/6.2026-0957

Journal information: American Institute of Aeronautics and Astronautics