This article was originally published in conversation. The publication contributed this article to Space.com Expert Voices: Columns and Insights. Marcos Fernandez Toss is a professor of aerospace technology at the University of North Dakota.
In December 2022, on the coast of Baja California, the sun shone on the sparkling sea and the waves crashed against the dock of the USS Portland. Navy officials on deck scanned the sky for signs. The light suddenly appeared.
What started as a tiny dot grew into a circle, falling from the edge of space at extremely fast speeds. This is from NASA Orion Capsulewhich will soon end a 25-day Artemis 1 mission around and beyond moon with a fiery splash Enter the ocean.
Orion reenters the atmosphere The capsule followed an acute-angle trajectory, falling at incredible speeds before deploying three red and white parachutes. As the mission completed a journey of more than 270,000 miles (435,000 kilometers), for those on the deck of the USS Portland, the capsule felt like a full homecoming.
as a rescue workerRaising Orion to the deck of an aircraft carriershock waves swept across the surface of the capsule. That’s when the crew began discovering large cracks in Orion’s lower surface, where the capsule’s exterior was bonded to its heat shield.
But why wouldn’t a shield that can withstand temperatures of 5,000 degrees Fahrenheit (2,760 degrees Celsius) be damaged? Looks natural, right?
This mission, Artemis 1, unmanned. But NASA’s ultimate goal is to send humans to the moon by 2026. (The current target is 2027. ) Therefore, NASA needs to ensure that any damage to the capsule (even to its heat shield, which would mean some damage) does not endanger the lives of future crew members.
The shield was severely damaged when Artemis 1 re-entered the atmosphere on December 11, 2022, causing the next two Artemis missions to be delayed. While engineers are now working to prevent the same issue from happening again, the new release date is targeting April 2026, and it’s coming soon.
as a Professor of Aerospace TechnologyI enjoy studying how objects interact with the atmosphere. Artemis 1 provides a particularly interesting case and demonstrates why having a functional heat shield is critical for space exploration missions.
take away heat
To understand what exactly happened to Orion, let’s review the story. When the space capsule re-enters Earth’s atmosphere, it begins skim its higher layerswhich acts somewhat like a trampoline, absorbing some of the kinetic energy of an approaching spacecraft. This maneuver was carefully designed to gradually slow down Orion and reduce thermal stress on the inner layers of the shield.
After the first dive, Orion bounced back into space in a calculated motion, losing some energy before diving again. As it approaches the ocean, a second dive will take it into denser lower layers of air, further slowing it down.
As it falls, the drag on the capsule from air particles reduces its speed from about 27,000 mph (43,000 km/h) to about 20 mph (32 km/h). But this slowdown comes at a cost—the friction of the air is so great that the bottom surface of the capsule facing the airflow reaches temperatures of 5,000 degrees Fahrenheit (2,760 degrees Celsius).
At such scorching temperatures, air molecules begin to break apart, Thermal Mixing of Charged Particlescalled plasma, is formed. This plasma radiates energy and you can see red and yellow burning air surrounding the front of the vehicle, wrapping it backwards in the shape of a candle.
No material on Earth could withstand such hellish conditions without serious damage. So the engineers behind these capsules designed a layer of material called a heat shield that would be sacrificed by melting and evaporating, saving the capsule that would ultimately house the astronauts.
By protecting anyone who might one day be inside a space capsule, The heat shield is a key component.
It is this shell that encloses the wide end of the spacecraft in the form of a skin facing the incoming airflow – the hottest part of the vehicle. It’s made from a material designed to evaporate and absorb the energy created by the friction of the air with the vehicle.
The case of Orion
But what exactly happened to Orion’s heat shield during its descent in 2022?
For Orion, the heat shield material is a composite Resin called novolac – Corresponding to the bakelite used in some gun manufacturing – absorbed in a honeycomb structure of fiberglass threads.
When the surface is exposed to heat and airflow, the resin melts and recedes, exposing the fiberglass. The fiberglass reacts with the surrounding hot air, creating a black structure called char. The char then acts as a second thermal barrier.
NASA uses the same heat shield design for its Orion spacecraft as it did for its Apollo capsules. But the charcoal structure did not crack as it did on Orion during the Apollo missions.
After nearly two years of analyzing samples of the charred material, NASA concluded that The Orion project team overestimated the heat flow when the spacecraft re-entered the atmosphere.
As Orion approached the upper atmosphere, the shield began to melt and gas produced May escape through pores in the material. Then, when the capsule gained altitude again, the outer layer of resin froze, trapping the heat generated during the first dive inside. This heat vaporizes the resin.
When the capsule dips into the atmosphere a second time, the gas expands, then heats up again and finds its way out – a bit like a frozen lake. Thaw from bottom up —and its escape Cracks on the capsule surface Where the carbon structure is damaged. These are the cracks rescuers saw after the capsule splashed down.
At a press conference on December 5, 2024, NASA officials announced that the Artemis 2 mission will use a modified reentry trajectory design to prevent heat accumulation.
For Artemis III, scheduled for launch in 2027, NASA intends to use new shield manufacturing methods to make it more permeable. During reentry, the outside of the capsule will still get very hot and the heat shield will still evaporate. But these new methods will help astronauts stay comfortable in the capsule during splashdown.
Chonglin ZhangAn assistant professor in the Department of Mechanical Engineering at the University of North Dakota assisted with research for this article. read Original article.