Press Release
BOLT Experiment Readies for Final Flight in Sweden
True to its name, BOLT aims to understand​ boundary layer transition — whether the air around the surface of a hypersonic vehicle is laminar (moving in a smooth manner) or turbulent (swirling in circles, and associated with up to eight times the heat transfer). Observing this flow around a hypersonic vehicle in flight is valuable; the resulting basic science knowledge can be transitioned to more applied efforts toward helping design hypersonic aircraft and missiles. However, multiple factors, including hypersonic vehicles’ shape and altitude, and the fact that they move faster than five times the speed of sound, make pinpointing this shift incredibly difficult.
Credit: Johns Hopkins APL/Angelica Butte and Steve Smith
After waiting over a year because of the pandemic, the Johns Hopkins Applied Physics Laboratory (APL) Boundary Layer Transition (BOLT) flight experiment team is preparing for a late-June launch campaign at the Esrange Space Center (SSC) in Kiruna, Sweden.
True to its name, BOLT aims to understand boundary layer transition — whether the air around the surface of a hypersonic vehicle is laminar (moving in a smooth manner) or turbulent (swirling in circles, and associated with up to eight times the heat transfer). Observing this flow around a hypersonic vehicle in flight is valuable; the resulting basic science knowledge can be transitioned to more applied efforts toward helping design hypersonic aircraft and missiles. However, multiple factors, including hypersonic vehicles’ shape and altitude, and the fact that they move faster than five times the speed of sound, make pinpointing this shift incredibly difficult.
An APL team developed and built the Boundary Layer Transition (BOLT) flight hardware with help from an Air Force research grant. BOLT’s long-awaited flight test is slated for late June.
Credit: Air Force Office of Scientific Research/Johns Hopkins APL
To understand this behavior, the Johns Hopkins APL team in Laurel, Maryland, built the BOLT hardware after being awarded a grant from the Air Force Research Laboratory’s Air Force Office of Scientific Research. Tapping the expertise of multiple academic, commercial and government groups, including NASA Langley, the Air Force Research Laboratory’s Aerospace Systems Directorate, University of Minnesota, Purdue University, Texas A&M University, CUBRC, Australia’s Defence Science and Technology Group, the German Aerospace Center (DLR) and VirtusAero, APL developed wind tunnel models and built the flight experiment hardware.
The project began in 2017 with wind tunnel testing and computer simulation work, and was headed to an actual flight in May 2020 that would provide much-needed data and validation — but the COVID-19 pandemic stalled BOLT’s launch as travel came to a halt.
Still, the APL team, along with DLR, the organization coordinating the launch campaign with SSC, did what it could while waiting for pandemic restrictions to ease and international travel to become possible once again.
“We made some progress on the postflight data analysis tools, but largely most of the research from here on out requires the flight data,” said APL’s Brad Wheaton, the principal investigator on BOLT. “This data will be critical to understanding the behavior of boundary layer transition on complex shapes and will be used to validate new prediction tools that will enable us to more precisely identify transition on future complex geometries.”
The vast wilderness of the Esrange Space Center in northern Sweden will not only serve as a picturesque backdrop for BOLT’s final flight but also make it easier for the team to recover the payload after launch.
Credit: Dorian Hargarten, DLR
The BOLT experiment hardware will rely on thermocouples, pressure sensors and heat-transfer gauges to mark the onset of boundary layer transition during flight. The vast wilderness of SSC’s rocket range and research center in northern Sweden will not only serve as a picturesque backdrop for BOLT’s final flight but also enable the team to more easily find and recover the payload after launch.
Team members will compare data from the launch campaign to what they learned from wind tunnel tests and simulations to see how well their prediction techniques stacked up and how they can further improve their methods. APL will also lead this subsequent research effort to analyze the flight data with academic and industry partners.
“The BOLT experiment will be the ultimate validation of the physics in the true flight environment,” Wheaton said.