India, April 11 --  Orion hit the first traces of Earth's upper atmosphere at 400,000 feet above the Pacific, traveling at almost 35 times the speed of sound. Inside the capsule, the four Artemis II astronauts pulled 3.9 Gs-about what you would feel on a really good roller coaster. Then the plasma came, and the radios went silent.

For exactly six minutes, mission control heard nothing. Plasma built up around the spacecraft as it raced through the atmosphere, temporarily blocking all communications. The heat shield faced peak heating, repelling temperatures of 5,000 degrees Fahrenheit-half as hot as the surface of the sun.

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The Artemis II crew breached the upper atmosphere sout...