23 years after Columbia disaster, one-of-a-kind 'plasma tunnel' recreates extreme conditions spacecraft face upon reentry
Story by Daniel Strain; photos by Patrick Campbell; video by Nicholas Goda
Picture a spacecraft returning to Earth after a long journey.
The vehicle slams into the planet’s atmosphere at roughly 17,000 miles per hour. A shockwave erupts. Molecules in the air are ripped apart, forming a plasma—a gas made of charged particles that can reach tens of thousands of degrees Fahrenheit, many times hotter than the surface of the sun.
The sight is spectacular to behold, but it’s also dangerous, said Hisham Ali, assistant professor in the Ann and H.J. Smead Department of Aerospace Engineering Sciences.
The is a tragic example. On Feb. 1, 2003, as the space shuttle reentered Earth’s atmosphere, plasma flooded into the vehicle through a defect in its shield of protective tiles. The shuttle disintegrated, and seven crewmembers, including CU Boulder alumna Kalpna Chawla, died.
Illustration showing NASA's Orion spacecraft returning to Earth. (Credit: NASA)
Ali has dedicated his career to helping prevent those kinds of accidents.
“One of the most critical and dangerous phases of any space mission is when spacecraft reenter Earth’s atmosphere,” he said. “If we’re taking more humans to orbit through space tourism, we need to do that safely and effectively, and that’s a challenging problem.”
Scientists call this kind of flight “hypersonic.” Vehicles hit hypersonic speeds when they travel at Mach 5, or five times the speed of sound, and faster. At sea level, that’s a blistering 3,800 miles per hour.
Ali and his team are trying to recreate the wild physics that occur at those speeds, entirely from the safety of the ground.
To do that, the group opened a new kind of research facility on campus in late 2025. Known as an inductively coupled plasma tunnel, the facility generates streams of plasma that flow at speeds of hundreds to thousands of miles per hour and burn at up to 9,000 degrees Fahrenheit and hotter.
He and his students are using this one-of-a-kind facility to test how new materials and other technologies behave in such a treacherous environment. They’re also exploring an out-there idea: whether engineers can use powerful magnets to actually maneuver vehicles flying at incredible speeds, something that’s not possible today.
“There’s not a chamber exactly like this anywhere in the world,” Ali said.
A lab that glows
That machine is coming to life now in a windowless lab on CU Boulder's East Campus. There, a 40-kilowatt generator roars on, and it’s hard to hear anything over the sound.
Ali and a small team of graduate students monitor a series of readouts on a computer terminal. Beside them are the main components of the group’s plasma wind tunnel: The first is a tube made of quartz glass, known as a nozzle, which is about the size and shape of a wine bottle. It feeds into a much larger chamber that’s sealed with stainless steel several inches thick.
“I think we’re ready to light,” Ali says to his team.
In an instant, a lavender-colored light blinks on in the quartz-glass tube. The eerie glow comes from a plasma, like the kind that threatens spacecraft when they return to Earth.
From there, the plasma rushes into the metal chamber, which you can peer into through a porthole window. Inside, every surface radiates orange from the heat.
To simulate the conditions of hypersonic flight the group needs two things: speed and heat.
To build up speed, he and his students inject a stream of argon gas into their tunnel. A powerful vacuum system then sucks that gas through the tunnel—and fast. The vacuum can pull more than 20,000 cubic meters of air per hour, making it one of the most powerful machines of its kind at any university in the United States.
The heat comes next. The researchers hit their plasma with strong radio waves that flip back and forth. Those waves generate electric currents within the gas, eventually causing it to explode into a plasma. Once the argon is lit, the team can then inject regular, Earth air into the tunnel.
“My students and I worked a lot of late hours to make this happen,” Ali said.
Staying cool
Ali’s own passion for hypersonic flight began on a school trip.
The engineer grew up in Alabama, and when he was in fifth grade, he attended Space Camp at the U.S. Space and Rocket Center in Huntsville. There, a guide pulled out a tile similar to the ones NASA engineers once used to shield space shuttles from heat during reentry.
“They put a blowtorch on one side and let us put our hands on the other. You could still feel that it was cool,” Ali said. “I thought that was very interesting.”
It kicked off Ali’s lifelong dream of helping humans explore the solar system—and come back safely.
The new plasma tunnel brings him one step closer to that goal.
Ali explained that he and his students can use a metal arm to lower almost anything—like a new type of heat-resistant material or design for a sensor—into the flow of their plasma. The streaming plasma instantly forms a shock wave around the obstruction. The team can then test how technologies behave under those kinds of extreme conditions.
The researchers have already collaborated with one aerospace company to test a new type of heat-resistant material. They have plans to work with several more companies in the months ahead.
But the facility does more than just capture Earth’s atmosphere in a bottle. It can also simulate the atmosphere of many other planets. What would happen, for example, if a space capsule rammed into Mars’ thin, carbon dioxide-rich atmosphere?
“Once our plasma is lit, we can inject carbon dioxide and create a plasma made of flowing carbon dioxide, similar to what a spacecraft might experience at Mars,” Ali said.
Hisham Ali inspects his plasma wind tunnel.
Room to maneuver
The team is tackling what might be the most persistent challenge of hypersonic flight: Once a vehicle hits those kinds of speeds, it’s nearly impossible to steer. That’s because anything that sticks out from a plane or spacecraft, like wings or flaps, would burn up almost at once. As a result, pilots can’t easily change a spacecraft’s trajectory after it reenters Earth’s orbit if something goes wrong.
Ali’s team hopes to get around that limitation with the help of an unusual property: magnetism.
Plasmas, Ali noted, are made of charged particles. If you have a powerful enough magnet, you can potentially change the flow of those charged particles, much like how you can use toy magnet to move around iron filings.
The researchers envision that future spacecraft could employ ultra-strong magnets to push on the plasma shock waves around them. In the process, they might build up enough force to turn—at least a little bit.
The team will soon start running experiments to test that idea.
For now, Ali is excited to see the culmination of a dream that began with a blowtorch all those years ago.
“Increasing humankind’s understanding of our world and others is something I’ve always found really inspiring,” he said.
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