After 10 days in space, a record-breaking lunar flyby and a journey that took them farther from Earth than any humans in more than 50 years, the four astronauts aboard NASA’s Artemis II mission are nearly home. But as of Friday, the most nerve-racking chapter of the mission is still unfolding.
NASA astronauts Reid Wiseman, Christina Koch and Victor Glover, along with Canadian Space Agency astronaut Jeremy Hansen, are set to return to Earth on Friday evening after 10 days in space. Their Orion capsule is scheduled to begin plunging through the atmosphere at around 7:53 p.m. ET, on a fiery journey expected to last less than 15 minutes, with a planned splashdown in the Pacific Ocean at 8:07 p.m. ET off the coast of San Diego.
A heat shield that was never ideal
Re-entry is always one of the riskiest parts of spaceflight, as vehicles can be exposed to temperatures of around 5,000 degrees Fahrenheit as they streak through the atmosphere. But that risk is especially pronounced for Artemis II, because the Orion spacecraft’s heat shield the critical layer of thermal protection at the bottom that protects astronauts from extreme temperatures has known flaws in its design.
The issue traces back to 2022. When Orion returned to Earth after the Artemis I uncrewed test flight, engineers found unexpected cracking and charring on the heat shield, with pieces of material breaking away. After a lengthy investigation, NASA determined the issue came down to the material itself, called Avcoat. As the heat shield burned away which it is designed to do gases built up inside the material. But in some areas, the shield was not porous enough to release that pressure, resulting in cracks and chunks breaking off during re-entry.
The Artemis II Orion spacecraft has a heat shield that is nearly identical to the one that flew on Artemis I. If the heat shield becomes damaged or cracks in a particular way, it could lead to catastrophic failure. And there is no escape mechanism that could save the astronauts during this point in the journey.
Dr. Danny Olivas, a former NASA astronaut who served on a space agency-appointed independent review team that investigated the incident, put it plainly, This is a deviant heat shield, there’s no doubt about it, this is not the heat shield that NASA would want to give its astronauts.
Why NASA didn’t simply replace it
For Artemis II, the capsule had already been built and assembled when NASA learned of the damage sustained during Artemis I. So, rather than redo the heat shield, NASA came up with a modified path for the capsule’s re-entry to minimize risk to the astronauts.
That fix was not about making modifications to the heat shield itself, but instead altering the space capsule’s re-entry trajectory, opting for a steeper angle that leads to higher heat levels but reduces the amount of time Orion and its crew spend enduring the most intense atmospheric resistance.
NASA also conducted extensive ground testing, recreating re-entry conditions using high-temperature testing facilities, wind tunnels and material analysis labs, and ran simulations of even more severe damage than what was seen on Artemis I, determining the spacecraft could still protect the crew within safety limits.
13 minutes where everything has to go right
The pressure on mission controllers today is significant. NASA’s Artemis II flight director Jeff Radigan said at a Thursday news briefing: We have to hit that angle correctly. Otherwise, we’re not going to have a successful re-entry. He described re-entry as 13 minutes of things that have to go right, and noted that mission controllers spent the past day and a half keeping Orion on the precise course required.
As Orion descends through about 400,000 feet, the spacecraft will enter a planned six-minute communications blackout at 7:53 p.m. as plasma forms around the capsule during peak heating. The crew is expected to experience up to 3.9 Gs in a nominal landing profile. After emerging from blackout, Orion will jettison its forward bay cover, deploy its drogue parachutes near 22,000 feet at 8:03 p.m., and then unfurl its three main parachutes around 6,000 feet at 8:04 p.m. to slow the capsule for splashdown.
Confidence, with eyes wide open
Despite the concerns, top Artemis II officials as well as the astronauts themselves have said they are confident that NASA understands the issue and that the capsule will return home safely. Olivas, for his part, has also said he believes NASA has the problem well in hand after conducting a thorough investigation.
Because of those issues, NASA will modify the heat shield design for future Artemis flights, with the Orion spacecraft used for those missions set to feature a more permeable layer of outer material. For Wiseman, Koch, Glover and Hansen, though, the mission comes down to what it has always been: 13 minutes, one heat shield and a splashdown that the world will be watching.
