May 6, 2015
Spacecraft re-entering Earth’s atmosphere are subjected to extreme heat, with air temperatures surrounding vehicles reaching above 8,000 Kelvin (near 15,000 degrees Fahrenheit)—a temperature hotter than magma.
ASE/EM researchers are planning to emulate these extreme re-entry temperature conditions on solid ground by using a plasma torch—a “flame” of superheated gas—to study how potential heat shield materials hold up. The flame will be able to reach re-entry temperatures as well as surpass them with a maximum temperature of 10,000 Kelvin, a value hotter than the surface of the sun.
Philip Varghese, professor and director of the Center for Aeromechanics Research, and Noel Clemens, professor and ASE/EM department chair, have received $570,000 from NASA Johnson Space Center (JSC) and the Cockrell School to build a torch facility at the J.J. Pickle Research Campus. It’s planned to be up and running by the end of 2015.
The research team will be working closely with JSC to test heat shield materials for the Orion spacecraft, a next-generation space exploration vehicle that NASA is building to shuttle a human crew to Mars.
“We are excited that JSC has chosen UT as a partner to develop this capability that is so critical to the success of the Orion program,” Clemens said.
The research goal is to identify potential shield materials that are thin, yet still able to undergo ablation, a process that turns a portion of the shield material into a gas that takes the heat with it as it leaves the rest of the material behind.
“The heat shield is in some sense the sacrifice and it burns or ablates away,” Varghese said. “And the idea is the [surface] should not get so hot that the stuff behind it starts to melt, nor should it burn away so quickly that you’re left without a shield.”
The emphasis on shield thinness is driven by the desire for a lighter spacecraft, Varghese said. The lighter the craft, the less it costs to send it to space, which allows funds to be spent on larger payloads instead.
One of the reasons why the team is using a plasma torch over other methods is that the gases that make up the torch’s flame can be adjusted to reflect the gases in Earth’s atmosphere—as well as gasses in exoplanet atmospheres that future spacecraft may encounter.
Another reason is that the plasma provides a “clean” burn. The plasma is formed in a quartz tube, and ejected through an opening in the form of a flame made up only of its composite gases. Other heating methods, such as those involving arc-jets, risk introducing metal impurities that could contaminate the shield materials and affect how they respond.
The planned experiments involve heating a small tile of shield material within the flame while laser-based sensors record values such as temperature and the composition of the ablated gas. These precise readings will allow Varghese and Clemens to record in detail how the shield material is affected by the torch, and enable NASA researchers to make informed decisions on shield materials.
“With a facility like this, we can better understand the existing materials, and [NASA] can cook up new materials and understand how they behave better so they can start thinking about the next generation of heat shield materials,” Varghese said.
“We see it as a joint venture,” added Randy Lillard, branch chief of thermal design at JSC. “We are going to provide help with the design, and put in some of our instrumentation and projects. But in the long term UT will have a facility where they can keep doing research and testing materials.”
