Spacecraft That Sweat? A Cool New Way to Tackle Atmospheric Reentry

A car may drive for 15-20 years before needing replacement, while a passenger jet may fly for up to 40. A spacecraft may only fly once. Even the longest-serving spacecraft, the space shuttle Discovery, completed only a few dozen flights, each requiring months of extensive testing and replacement of critical pieces. As space travel becomes more common, the need for fully reusable spacecraft is growing. One potential solution? A spacecraft that sweats.

The Department of Aerospace Engineering at Texas A&M University is partnering with Canopy Aerospace to develop and test a 3D-printed material that releases or "sweats" a coolant gas to protect spacecraft. This technology, part of a $1.7 million Air Force Small Business Technology Transfer grant, could enable the design of fully and rapidly reusable spacecraft.

The most significant hurdle in making a spacecraft fully reusable is withstanding the intense heat it encounters when reentering the atmosphere at high speeds. Traditional spacecraft rely on heat shields that burn away completely or ceramic tiles that may need replacement between flights. Modern spacecraft like SpaceX's Starship demonstrate a higher degree of reusability by using more advanced heat shields than their predecessors.

A sweaty spacecraft could abandon heat shields altogether and utilize a method called transpiration cooling. This method creates a layer of gas along the vehicle's surface that not only cools the spacecraft but also acts as a barrier preventing direct contact with the hot atmosphere.

"Gas has a very low thermal conductivity," said Dr. Hassan Saad Ifti, assistant professor of aerospace engineering in the department. "This is why a puffer jacket is so effective. It traps air in these pockets, so it is the insulation from the air keeping you warm, not the solid part of the jacket."

Because the sweated gas insulates the vehicle, single-use heat shields are no longer needed. This could reduce the time between flights from months, as seen with the space shuttle, to a matter of hours, closer to the turnover time of a passenger jet.

The idea of using gas as an insulator for spacecraft has existed for decades, but it is not as simple as strapping a puffer jacket to a rocket. Until now, limitations in materials science, computational power and ground testing abilities have made it challenging to implement.

This project will connect Canopy Aerospace's materials science capabilities with Texas A&M's state-of-the-art testing facilities and the aerospace engineering researchers' hypersonics expertise to overcome those limitations.

"We are in a great position to bring together expertise on aerodynamics and high-speed testing to ensure this project succeeds," said Dr. Ivett Leyva, department head of aerospace engineering.

For transpiration cooling in spaceflight to be successful, the spacecraft's hull material must be strong enough to withstand extreme pressures yet porous enough for the coolant to sweat through. Canopy Aerospace has already developed the material—a 3D-printed silicon carbide. The first batch of prototypes has been sent to Texas A&M for high-speed testing.

William Matthews, a fourth-year Ph.D. student, is leading the development of testing rigs to evaluate the material's effectiveness — both in how well it sweats gas and how well that gas insulates a spacecraft.

"We should see that the material's surface is cooler at hypersonic speeds when the coolant flow is introduced than the baseline when no coolant is present," Matthews said. "Depending on how well the gas permeates the material, there are a lot of potential outcomes for this technology, and these tests should help us decide which direction we want to go."

The initial wind tunnel testing at Texas A&M Engineering Experiment Station's National Aerothermochemistry and Hypersonics Laboratory will provide basic understanding of the physics behind transpiration cooling in spaceflight. The results will help Texas A&M and Canopy Aerospace determine the requirements for a full-scale mission and build the foundation for commercial use of the technology.

"I am optimistic about this technology," said Ifti. "If all goes well, we could see sweaty spacecraft in the sky by the end of our lifetimes."

Provided by Texas A&M University College of Engineering