After spending 10 days in space on the first crewed lunar mission in more than 50 years, the astronauts of Artemis II are now preparing for the most critical and risky phase of their journey which is returning to Earth.
According to NASA, reentry is widely considered one of the most dangerous parts of any space mission.
What makes the reentry so dangerous?
When the Orion spacecraft comes back to Earth, it will be moving at about 25,000 miles per hour which is more than 30 times the speed of sound, according to CNN. At that speed, the air around it gets compressed which makes the outside of the capsule heat up to over 5,000 degrees Fahrenheit.
The only thing protecting the astronauts from this extreme heat is the heat shield. If it fails, there is no backup and no escape system at that stage.
“The Orion spacecraft will enter the Earth’s atmosphere at approximately 25,000 miles per hour. That heat shield will bear the full force of that reentry,” NASA official Amit Kshatriya said, as per CNN. “Every system we’ve demonstrated over the past nine days, life support, navigation, propulsion, communications, all of it depends on the final minutes of flight.”
NASA’s flight director Jeff Radigan explained how critical this phase is: “It’s 13 minutes of things that have to go right,” he said, according to NBC News.
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The heat shield problem
This concern is real and not just theoretical. After the Artemis I test mission in 2022, teams found that the heat shield had cracks and damage, according to CNN. Investigators later said this happened because gas pressure built up during re-entry.
The issue for Artemis II is that it is using almost the same heat shield design as Artemis I and by the time the issue was discovered, it had already been installed, so it could not be redesigned.
NASA has admitted the shield is not perfect. Former astronaut Dr Danny Olivas said, “This is a deviant heat shield.” He added, “There’s no doubt about it: This is not the heat shield that NASA would want to give its astronauts.” Still, he said he believes NASA “has its arms around the problem.”
Astronaut Victor Glover said, “I’ll be honest and say, I’ve actually been thinking about entry since April 3, 2023, when we got assigned to this mission,” according to CNN. “One of the first press conferences, we were asked, what are we looking forward to? And I said, splashdown. And it’s kind of humorous, but it’s literal as well that we have to get back.”
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How NASA is managing the risk?
To reduce risk, NASA has changed the way the spacecraft will return to Earth. Instead of the “skip” re-entry used in Artemis I, Artemis II will follow a “loft” trajectory to reduce heat stress and limit cracking.
Mission commander Reid Wiseman said, “If we stick to the new reentry path that NASA has planned, then this heat shield will be safe to fly,” as per CNN.
NASA Administrator Jared Isaacman has also expressed “full confidence” in the Orion heat shield, according to NBC News.
After splashdown, a diver will photograph the heat shield from below to check its performance.
NASA leaders remain confident. The agency says it has studied the issue in detail and believes the modified reentry plan will keep the crew safe.
