There’s an unlikely and little-known connection between NASA’s Artemis II lunar mission and one of Hans Bethe’s most practical yet least celebrated contributions from the late 1950s.
While consulting for AVCO on ICBM reentry vehicles, the Nobel laureate teamed up with engineer Mac Adams to publish a landmark 1959 paper: “A Theory for the Ablation of Glassy Materials.” The problem they tackled seemed almost impossible at the time: a nose cone slamming back into the atmosphere at Mach 25 would be enveloped in plasma hotter than 5,000 °F. Any normal material would simply vaporize. Pure insulation wouldn’t work; it would have to be impractically thick. Bethe and Adams realized the solution wasn’t to resist the heat but to embrace controlled sacrifice. They focused on glassy materials like fused quartz and glass-phenolic composites that would melt rather than char or burn chaotically.
Here’s what their theory showed: The outer surface reaches melting point and forms a thin, viscous liquid film. The hypersonic airflow shears this molten layer away, blowing it off as gas and droplets. The energy is carried outward and is absorbed in melting, vaporization, and convection instead of conducting inward. The ablation front steadily recedes, layer by layer, but the solid material behind it stays near room temperature. A shield only about an inch thick is enough. It was active cooling by mass loss, not passive protection. The heat shield literally burns away, turning the incoming plasma’s fury into exhaust that protects the vehicle.
That same foundational physics underpins today’s Orion capsule heat shield for Artemis II. Orion uses Avcoat - the only difference being that it is a charring ablator instead of a melting, glassy one, but descended from the same principles. The outer blocks pyrolyze and char at thousands of degrees, releasing gases that block the plasma and carry heat away, while the interior stays cool enough for the crew.
So when you watch Orion plunge through the atmosphere at 25,000 mph with its glowing plasma sheath, you’re seeing 1950s nuclear-missile research - refined by one of the 20th century’s greatest theoretical physicists - still keeping astronauts safe on the way back from the Moon. ICBM tech to lunar return. Science really is the ultimate long-term investment.
Look at this astronaut's face during reentry, knowing the capsule exterior is at 5,000°F.
The physics of why he's alive are wild.
The air in front of the capsule compresses so violently at Mach 25 that it turns into plasma. 5,000°F on the surface. Half the temperature of the sun. The heat shield absorbs that energy by literally burning itself away, layer by layer, carrying the heat with it as gas.
One inch of material is the entire margin. On the outside of that inch: 5,000°F. On the inside: 75°F. Room temperature. The thermal gradient across that single inch is the steepest temperature drop humans have ever engineered.
The orange glow in the window is ionized nitrogen and oxygen. That plasma is why comms go black for six minutes during reentry. Ground control can't reach the crew. The astronauts are alone inside a fireball, falling at 25,000 mph, watching the laws of thermodynamics keep them alive through a 1-inch wall.
Artemis II did exactly this last night. Four astronauts hit Earth's atmosphere at 24,664 mph, rode a 4,900°F plasma sheath for six minutes of radio silence, and splashed down a mile from target.
The heat shield is now being inspected for cracks. They found over 100 on the last unmanned test.