NASA is testing heat shields that can keep astronauts safe as they return from missions to the Moon and Mars in an unusual way: by taking out the trash.

When Northrop Grumman 24^th cargo resupply mission for NASA undocked from the International Space Station, it carried a fleet of 12 small, experimental capsules designed to test the next generation of thermal protection materials that could serve as the foundation for future heat shields.

The experiment, called the Kentucky Reentry Probe Experiment (KREPE-3), is the third in a series of low-cost, high-impact missions that use the final moments of the cargo spacecraft’s lifespan to gather valuable data.

The experiment is a collaboration among the University of Kentucky, the state of Kentucky, NASA’s Established Program to Stimulate Competitive Research (EPSCoR), several NASA centers, and other federal and commercial partners.

“KREPE-3 is a great example of the goals of NASA’s EPSCoR program,” said David Berger, EPSCoR program manager at NASA’s Headquarters in Washington. “We are supporting the next generation of scientists and engineers as they develop unique projects that benefit their education and NASA’s mission goals.”

Trash to treasure

Before the mission’s Cygnus XL spacecraft departed the station, astronauts packed it with waste and activated the 12 small capsules carried inside. Designed by University of Kentucky students, the capsules include sensors that will measure temperature, pressure, motion, magnetic field, and light during re-entry. 

As the vehicle harmlessly breaks apart in Earth’s atmosphere on its planned route, the capsules will eject and begin collecting data on how each set of experimental heat shield materials performs. Satellite signals will transfer live data to researchers, offering insights into how larger heat shields could protect future cargo or crew.

“It’s a smart way to get flight data on materials that are still in development,” said Keith Peterson, a materials engineer at NASA’s Ames Research Center in California’s Silicon Valley. “We’re essentially hitching a ride on a vehicle that’s already coming back to Earth.”

Heating up innovation

The capsules will carry a variety of thermal protective components, including proven technology such as the ceramic tile material used on the space shuttle. Others will test new options, such as a 3D-printed heat shield from the Additive Manufacturing of Thermal Protective Systems project developed at NASA Johnson and Oak Ridge National Laboratory.

Researchers at NASA Ames are contributing several materials to KREPE-3, including two capsules that will fly a next-generation family of protective coverings known as Materials Engineered for Re-entry using Innovative Needling Operations (MERINO). Made from layers of carbon and phenolic fibers stitched together like felt, the materials are more flexible, faster to produce, and less expensive than traditional protective substances – making them promising candidates for Mars missions. Thanks to Mars’ thinner atmosphere, missions to land on the Red Planet involve lower heat loads and allow for lighter protection.

A third capsule will combine those protective coverings with other elements. The Kentucky Instrumented Conical Hypersonic Experiment will utilize a dual-cone shape. It combines a tungsten tip attached to a cone layered with carbon and hear-resistant plastic fibers, and an aft cone wrapped in MERINO. This unique design will validate computer models against real-world data.

Another capsule is shaped like the protective aeroshell that will protect NASA’s upcoming mission, Dragonfly, as it arrives at Saturn’s moon, Titan, and will test the dynamic stability of the design. It is covered in Phenolic Impregnated Carbon Ablator, a material developed at NASA Ames that has applications for commercial vehicles and flew on NASA’s Stardust, Mars Science Laboratory, and Mars 2020 missions.

One capsule will test a deployable heat shield called Adaptable Deployable Entry and Placement Technology, which is shaped like an umbrella to increase surface area and slow descent. At full scale, Adaptable Deployable Entry design could be folded, making it ideal for deploying payloads that are larger than the rockets that launch them into flight.

While some capsules are testing new materials to carry missions to Mars, others are testing new shapes and designs that will further research and understanding of computer modeling and sensor design — technologies that could open doors to another generation of re-entry design innovation.

Additional capsules developed by domestic and international partners will test a variety of known and new materials, including a heat flux sensor developed at the University of Stuttgart in Germany, that will help researchers measure how heat moves across a surface during re-entry.

“We’re pushing the boundaries of what heat shields can do,” said Peterson. “And we’re testing them in a way that’s fast, affordable, and incredibly effective.”