NASA sends 12 heat-shield test capsules aboard departing Cygnus spacecraft

NASA said on Oct. 9 that 12 experimental heat-shield capsules had departed the International Space Station inside a Northrop Grumman Cygnus XL cargo spacecraft. The capsules are intended to gather measurements when the cargo craft breaks apart during its planned re-entry into Earth’s atmosphere, giving researchers flight data on materials being considered for future spacecraft.

The mission, called the Kentucky Reentry Probe Experiment 3, or KREPE-3, uses a cargo vehicle already headed for disposal. Astronauts activated the capsules and packed them inside the spacecraft alongside waste before departure, according to NASA. The plan calls for the capsules to eject as the vehicle breaks apart and send their measurements to researchers by satellite. NASA has not reported that this release or transmission has happened.

What the KREPE-3 capsules will measure

Each capsule carries sensors designed to record temperature, pressure, motion, magnetic field and light. Those measurements could show researchers what happens to the experimental protective materials under actual re-entry conditions. NASA Ames materials engineer Keith Peterson described the approach as a way to obtain flight data for materials still in development by using a spacecraft already returning to Earth.

The materials are deliberately varied. NASA says the payload includes established ceramic tile of the kind used on the space shuttle, as well as a 3D-printed heat shield developed by NASA’s Johnson Space Center and Oak Ridge National Laboratory. NASA Ames is contributing other protective materials. Comparing their behavior in flight is an aim of the experiment; the current announcement contains no KREPE-3 performance comparison.

Another capsule, the Kentucky Instrumented Conical Hypersonic Experiment, combines a tungsten tip, carbon and heat-resistant plastic fibers, and MERINO. NASA says its measurements are intended to test computer models against flight data. Other designs include a capsule shaped like the aeroshell planned for NASA’s Dragonfly mission to Saturn’s moon Titan and a deployable, umbrella-like heat shield designed to increase surface area and slow descent.

NASA also describes partner tests of other materials and designs, including a University of Stuttgart heat-flux sensor intended to measure how heat moves across a surface during re-entry. These are experiments on small capsules, rather than demonstrations that any of the materials is ready to protect an operational crewed spacecraft.

Why researchers need re-entry data

In a March report, Kentucky Educational Television interviewed University of Kentucky researchers about KREPE-3. They described flight testing as a way to observe conditions that are difficult to reproduce on the ground. One researcher explained the design trade-off: adding protective material increases weight and size, while a heat shield still has to protect astronauts or samples returning through the atmosphere.

KREPE-3 follows two earlier flights. NASA said two KREPE-1 capsules recorded and relayed temperature measurements during re-entry in December 2022. Five student-built KREPE-2 capsules flew aboard a Cygnus spacecraft in July 2024; according to NASA, all survived temperatures above 4,000 degrees Fahrenheit and transmitted data through the Iridium satellite network.

NASA said the KREPE-2 measurements included temperature, pressure, acceleration and angular velocity, while a tested spectrometer captured shockwave spectral data. Its November 2024 account said analysis was underway to inform spacecraft design and later experiments. University of Kentucky principal investigator Alexandre Martin identified transmission from every capsule as that flight’s principal achievement. Those earlier results show the approach has returned data before, but they do not establish the outcome of KREPE-3.