The astronauts’ safe return tonight was by no means a sure thing. They were flying a spacecraft that had never carried crew before and entering the atmosphere on a trajectory that had never been attempted before, protected by a heat shield that had caused engineers worry ever since the flight of Artemis I in 2022.
During the remainder of the trip the crew was not so much flying toward the Earth as falling toward it, following a gravitational plunge that saw them moving faster and faster as they drew closer and closer until they were moving at a blistering 24,000 mph—or 6,500 mph faster than spacecraft in orbit around the Earth move. That’s a lot of energy with which to crash into Earth’s thick atmosphere, and the crew spent all of today preparing for that high-stakes rendezvous.
The astronauts’ workday began at 11:35 a.m. EDT, when NASA piped up the song “Lonesome Drifter,” by Charly Crockett—the latest in a playlist of wake-up calls that, on earlier days, included "Working Class Heroes (Work)" by CeeLo Green, "Good Morning" by Mandisa and TobyMac, and “Under Pressure” by Queen and David Bowie. The crew spent the next few hours stowing 10 days’ worth of gear and tools, securing all loose objects to ensure that nothing would fly free during the violent shaking and the increase in gravity that would mark the capsule’s entry into the atmosphere. At 2:53 p.m., they fired their thrusters for what is called the Return Trajectory Correction 3 Burn, which put them on the proper path to enter the atmosphere over Hawaii and hit the waters off San Diego.
As with the Apollo spacecraft, Orion’s heat shield is made principally of a material known as Avcoat, a combination of epoxy resin and silica fibers, designed to absorb the fires of reentry and slowly burn off, or ablate, carrying the reentry heat away from the capsule and crew. That’s a big job, given that the heat shield must withstand temperatures of 5,000°F, half as hot as the surface of the sun, and significantly hotter than the 3,000°F a spacecraft returning from Earth orbit endures. Unlike Apollo’s heat shields, however, Orion’s had serious R&D problems.
In November of 2022, the Artemis I spacecraft took off for an uncrewed flight around the moon, as a first test of the Orion capsule and the giant Space Launch System moon rocket. The mission flew flawlessly—until it didn’t. When the crew capsule was recovered from the ocean, technicians were alarmed to find that the heat shield was covered with more than 100 cracks and large divots where the Avcoat had failed and flaked away. Any one of those locations could have allowed the heat of reentry to burn through the aluminum alloy walls of the spacecraft, killing any luckless crew that may have been inside, in much the kind of reentry breakup that doomed the shuttle Columbia and its seven-person crew in 2003. It was little more than dumb luck that none of the flaws in the Artemis I heat shield led to such a burn-through event.
What was the Artemis II re-entry trajectory?
Additionally, NASA eased Artemis II’s coast back to Earth. Artemis I followed a reentry route pioneered by the Apollo missions called skip-entry. Rather than plunging directly into the atmosphere the way slower-moving Earth-orbiting spacecraft do, the Apollo ships roller-coastered into the atmosphere, then up and out again, and then back in, bleeding off heat and gravitational forces along the way. That proved too much for Artemis I. So for Artemis II, NASA split the difference, not quite following the as-the-crow-flies route of Earth-orbiting craft, but taking a somewhat shallower path than Artemis I did. In the run-up to today’s reentry, NASA brass knew they were playing with fire—literally—but remained cautiously optimistic about their plan.
“It’s impossible to say that you don’t have irrational fears left,” said Amit Kshatriya, NASA associate administrator. “I would tell you I don’t have any rational fears about what’s going to happen. We’ve done the work we have to, and we have full confidence in the recovery team, the flight control team, and the analysis of the work we did.”
Splashdown has been achieved. That history can now be written.
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