HOUSTON, United States (AFP) — The Artemis II astronauts conducted a historic lunar flyby, gathered invaluable data and took in unprecedented Moon views, but one of the most crucial moments of their 10-day mission is still to come: Friday’s splashdown.

Earlier this week, Americans Reid Wiseman, Victor Glover and Christina Koch along with Canadian Jeremy Hansen voyaged further from Earth than any human before, in a mission considered a key stepping stone towards eventual crewed lunar landings, and more.

They are scheduled to splash down in the Pacific Ocean off the coast of San Diego at 5:07 p.m. local time, after which US space agency NASA and the military will help them get out of the capsule and fly them to a recovery ship.

Their journey has been rich in milestones and already resulted in stunning photographs that have captivated the imaginations of people on Earth.

But until the astronauts are home safe, it’s too early to talk about success, NASA’s Associate Administrator Amit Kshatriya told a briefing Thursday.

“When we can start celebrating is when we have a crew safely in the medbay of the ship,” the high-ranking official said. “That’s really when we can allow the emotions to take over, and, you know, start talking about success.”

“We need to have the crew home before we do that.”

Vital heat shield

The stakes are particularly high given concerns that arose during Artemis I, a 2022 uncrewed test flight to the Moon and back that saw the Orion heat shield erode in unexpected ways.

The heat shield is vital: During their reentry, the Orion spacecraft will face temperatures peaking around 2,760 degrees Celsius, or half as hot as the surface of the Sun.

The astronauts will come hurtling back at a maximum velocity of 10,657 meters per second — more than 30 times the speed of sound.

The heat shield is meant to slowly erode — “ablate,” as NASA puts it — to protect the capsule, a process that during Artemis I was disrupted.

To minimize any risk to the crew, NASA has changed the reentry path they had used in that test mission, after determining it had played a role in the complications.

“We have high confidence in the system and the heat shield and the parachutes and the recovery systems we put together,” Kshatriya said. “The engineering supports it, the Artemis I flight data supports it. All of our ground test supports it. Our analysis supports it.”

“And tomorrow, the crew is going to put their lives behind that confidence.”

Asked later about stress levels on the ground, NASA’s associate administrator said “it’s impossible to say you don’t have any irrational fears left.”

“But I would tell you, I don’t have any rational fears about what’s going to happen.”