This fear for the Artemis 2 Moon crew gives Nasa chief sleepless nights

The heat shield at the base of the Orion spacecraft is what stands between the crew and extreme temperatures during re-entry, but doubts remain around it due to what happened during the Artemis 1 mission.

In Short

• Artemis 2 astronauts returning, splashdown on April 11 at 5:37 am IST
• Heat shield faces an extreme of 2,760°C, causing plasma sheath and radio blackout.
• Nasa is confident structure will protect crew despite intense heat during reentry.

After days of travelling farther from Earth than any human in history, the four astronauts aboard Nasa’s Orion spacecraft are finally on their way back.

The Artemis 2 crew, comprising Reid Wiseman, Victor Glover, Christina Koch, and Jeremy Hansen, is scheduled to splash down off the coast of San Diego at approximately at 5:37 am IST on April 11.

But the mission isn’t over yet. The most nerve-wracking leg is still ahead, and it's the re-entry of the spacecraft back into Earth's atmosphere.

"In terms of what keeps me up at night, my blood pressure will be elevated until they [Artemis-II crew] are under parachutes in the water off the west coast," said Nasa administrator Jared Isaacman.

WHAT WILL HAPPEN WHEN ARTEMIS-II REENTERS EARTH?

During re-entry, about 122 kilometres above Earth, Orion’s service module will separate from the crew capsule. The capsule then plunges into the atmosphere at roughly 40,000 kilometres per hour.

At that speed, air molecules ahead of the spacecraft compress violently, heating the exterior of the capsule to around 2,760 degrees Celsius. For several minutes during this phase, a plasma sheath generated by this intense compression forms around the vehicle, blocking all radio communication between the crew and mission control.

After surviving peak heating, two parachutes will deploy to slow Orion to roughly 480 kilometres per hour, followed by three other pilot parachutes and then three main parachutes, which bring the capsule down to about 27 kilometres per hour before splashdown.

WHY IS REENTRY RISKY?

"Look, re-entry, you saw that massive rocket, 8.8. million pounds of thrust, that put a lot of energy in a very small spacecraft," said Isaacman. "All of that energy has to be taken out when it slams back into the atmosphere when coming back from the Moon. And there's no plan Bs there."

The heat shield at the base of Orion is what stands between the crew and those extreme temperatures, but doubts remain around it due to what happened during the Artemis 1 mission.

When Nasa retrieved the Orion capsule after the uncrewed Artemis 1 test flight in 2022, engineers discovered that material from the heat shield had broken off in chunks during re-entry.

That was not how it was designed to behave. Engineers eventually concluded that the gases trapped inside the shield’s material had built up pressure and caused it to crack when exposed to intense heat.

"I have no doubt the team did the right analysis on this, and we altered the mission profile," Isaacman noted. "The whole re-entry profile is very different than Artemis 1 to account for what I would describe as the shortcomings of the current heat shield on that vehicle."

This time, rather than replacing the shield, Nasa has instead opted to modify Orion’s re-entry path for Artemis 2, skipping the manoeuvre that was used during Artemis 1.

Instead, Orion will fly a steeper, more direct path to reduce heat exposure.

Nasa’s analysis concluded that even under conditions exceeding those expected during re-entry, the heat shield would remain intact and protect the crew.

"So I am going to be thinking about that constantly until they are back in the water," Isaacman added.

- Ends