UT engineers work with NASA to put spacecraft in the hot seat

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Things are heating up as UT engineers find new ways to test spacecraft heat shields. 

Philip Varghese, aerospace engineering professor, and Noel Clemens, aerospace engineering department chair, are collaborating with NASA to study how spacecraft heat shields react to intense heat during reentry into the atmosphere. Researchers are using a plasma torch, which generates extremely hot ionized gas, to simulate reentry conditions. 

When a spacecraft enters the atmosphere during its descent to Earth, it rubs against gas particles, which creates drag and slows down the spacecraft. The friction created during reentry also creates large amounts of heat, exceeding the melting point for many known materials. Varghese said space shuttles weighing up to 100 tons come into the atmosphere at around 18,000 miles per hour, generating kinetic energy equivalent to one-fourth of the energy of the atomic bomb that detonated over Hiroshima.

Engineers deal with this issue by placing heat shields on the spacecraft which char away during reentry, Varghese said. Once the spacecraft reaches the ground, engineers can replace the heat shield material and reuse the spacecraft for future missions.

“The idea is that you start with a sacrificial layer — essentially, something designed to burn away a little bit,” Varghese said. “In the process of burning away, it takes away the energy of the hot gases and the hot gases burn away over the surface.”

During a recent test with the spacecraft Orion, NASA noticed that the closer Orion got to Earth, the hotter the heat shield became. Even when the air cooled, the temperature of the spacecraft unexpectedly continued to rise and the heat shield’s material continued to char away. 

With funding from NASA’s Johnson Space Center, Varghese and Clemens are leading a team attempting to verify these results. The team will use a plasma torch to simulate the conditions of reentry. 

“We’re testing whether (the heat shield getting hotter) is a real effect or just a part of their simulation,” said Benton Greene, aerospace engineering graduate student and researcher on the project. “What we’re going to do is simulate the last bit of that reentry profile using the plasma torch and see if we can recreate those conditions.” 

The plasma torch is currently being tested to see what conditions, in terms of temperature and flow rate, it can simulate. Greene said the project will test the materials of multiple heat shields, including the similar materials used by spacecrafts Orion and Apollo. Greene said that in the future, researchers may install a vacuum chamber at the Pickle Research Center in order to better simulate real-world atmospheric pressures and temperatures. The team may also use the torch to test other materials as candidates for use in heat shields, Varghese said.

Varghese added that the tests could be used to aid developments in space exploration.

“With suitably prepared test gases you could simulate, on the ground, things that are representative of what a spacecraft probe might encounter when it enters the Martian or Venusian or Titan atmosphere,” Varghese said. “That’s a longer term goal — to make studies for entries into other bodies in the solar system.”