NASA on Thursday said it intends to attempt the launch of a historic, 10-day mission around the moon and back in April, following slips from launch windows in February and March.
Officials also acknowledged the mission—as with any journey beyond low-Earth orbit—may risk the lives of four crewmembers.
Following a flight readiness review, NASA teams polled “go” to attempt the launch on April 1, with additional opportunities in the five subsequent days and April 30. On Thursday, the space agency plans to roll its Space Launch System (SLS) rocket and Orion capsule—the two spacecraft handling the mission—from its Vehicle Assembly Building (VAB) to Launch Complex 39A at Kennedy Space Center in Florida.
Artemis II is intended to test systems and mission profiles ahead of future lunar landing attempts under Artemis, starting as soon as 2028.
“It’s a test flight and it is not without risk,” Lori Glaze, deputy associate administrator of the NASA branch that manages systems development for the Artemis campaign, said during a news conference Thursday. “But our team and our hardware are ready.”
NASA has conducted two wet dress rehearsals for the Artemis II launch, loading the SLS with more than 700,000 gallons of liquid oxygen and liquid hydrogen propellant and completing a mock countdown. However, Glaze said the next time the vehicle is loaded will be when it flies for real.
“We don’t feel like we need another wet dress, and this is one of those opportunities where I think…we’re using good technical judgment and being bold, making bold decisions about what we do,” said John Honeycutt, manager of the SLS program at NASA’s Marshall Space Flight Center in Alabama and chair of the Artemis II mission management team.
NASA Weighs the Risk
Honeycutt estimated that the risk of failure during Artemis I—the first, uncrewed flight of SLS and Orion in 2022—was about 50-50.
“The way I got the 1 in 2 is to just go look at the rockets that flew their first mission,” Honeycutt said. “How many of them were successful? It’s about 1 in 2.”
Honeycutt said a 1-in-50 threshold for Artemis II would be a “good number.” But because the mission has been long delayed, Glaze said, NASA will take on “significantly more risk than a mission or a flight system that’s flying all the time.” Honeycutt said the figure is likely “closer to 1 in 2.”
“We’re probably not 1 in 50 on the mission going exactly like we want to, but we’re probably not 1 in 2 like we were on the first flight,” he said.
Officials declined to give a firm assessment of risk due to the novelty of flying SLS and Orion with crew for the first time. An audit published this week by NASA’s Office of Inspector General (OIG) found that the space shuttle program believed it was operating at a 1-in-100 crew loss threshold. Later research determined it was really 1 in 10, the same as the Apollo missions, highlighting the fickle nature of such predictions.
“I think we’re being really careful not to really lay probabilistic numbers on the table for this mission, just given the small amount of data,” Honeycutt said.
He said the mission phases with the highest level of risk will be ascent, the perigee raise burn that lifts Orion’s Earth orbit, and the translunar injection burn that will send the Artemis II crew further from Earth than any human has ever flown.
Per the OIG, NASA’s crew loss threshold is 1 in 40 for lunar missions and 1 in 30 for Artemis missions overall. For comparison, the figure for crew swap missions to the International Space Station (ISS) is about 1 in 500, and about 1 in 200 for a 210-day stay at the orbital laboratory.
The report further found limitations in the agency’s ability to conduct crew survival analyses. It determined that NASA has “ruled out” crew rescue capabilities for the first crewed moon landings under Artemis, which are scheduled for 2028.
Crew Weighs In
Glaze said the Artemis II crewmembers—NASA astronauts Reid Wiseman, Christina Koch, and Victor Glover and Canadian Space Agency astronaut Jeremy Hansen—attended Thursday’s flight readiness review, giving them a chance to express any concerns they had with the mission.
“They did convey some of the things that they think about and the things that they worry about as the crewmembers, the kinds of risks that were of most concern to them,” Glaze said.
One involved the Orion crew capsule’s heat shield. The vehicle is coated in an outer layer of material called Avcoat, designed to protect the crew against temperatures up to 15,000 degrees Fahrenheit. Engineers predicted it would work just fine on Artemis I. But after the mission, they found the heat shield suffered higher than expected erosion during the reentry phase, when it experiences peak heating.
Rather than replace the heat shield for Artemis II, a NASA executive council voted unanimously to modify Orion’s reentry profile, capping a buildup of gases that is believed to have caused the Avcoat to crack. A new shield will be installed for Artemis III.
Glaze said program managers and the astronauts have “all agreed that we’ve got a good heat shield.”
“The question was, are we gonna be able to hit that entry interface and get them back on Earth safely?” she said.
Entry interface is the phase of the mission when Orion’s reaction control system engines steer the heat shield toward Earth. Until that point, it remains covered. Superheated plasma will form around the vehicle and temporarily block crew communications. The heat shield is meant to absorb that energy, allowing the capsule to slow down and gently parachute into the ocean.
“The main thing that I want to do is I want to hit that damn entry interface right down the middle and make sure that I bring the crew home safely,” said Honeycutt.
Glaze said the crew also talked about risks to communication with mission control and the performance of environmental and life support systems.
“One of the things that they mentioned was, we’ve spent the last 25 years in low-Earth orbit, and they wanted us to make sure that we all recognize…that this mission is different,” she said. “We are going well beyond low-Earth orbit. We’re going out to the moon, and we can’t always rely on our experience in low-Earth orbit when we’re taking on this kind of a mission.”
No More Dress Rehearsals
Glaze said NASA is not planning a third wet dress rehearsal (WDR) for Artemis II.
During the first WDR in early February, a liquid hydrogen leak near the quick disconnect interface of the tail service mast umbilical—used to load the SLS core stage with propellant—“spiked” at about T-5:15 in the mock countdown, prompting a ground launch sequencer to automatically halt it. Engineers repaired those seals and replaced some filters in ground systems on the launch pad. Teams also suffered multiple communications “dropouts” during the test.
Glaze said a second WDR “went very, very smoothly,” as teams loaded propellant on schedule without any leaks. They also hit their timeline for practicing closeout operations, during which astronauts are secured in Orion. Teams did lose communications early in the mock countdown, but they were quickly restored.
“Every time we tank the vehicle, it takes a little bit of the life out of those tanks,” said Glaze. “We certainly want to test and always make sure that everything’s working. But we’ve now done a couple wet dress rehearsals…when we tank the vehicle the very next time, I would like it to be on a day that we could actually launch.”
After the second exercise, engineers were unable to flow helium to the SLS interim cryogenic propulsion stage, which is required to pressurize its fuel tanks and keep its engine in good shape before launch. That prompted NASA to roll SLS and Orion back to the VAB, where engineers in March repaired a dislodged seal.
Though often necessary, transporting the spacecraft is resource-intensive. They travel on NASA’s crawler-transporter 2 (CT-2), which is about the size of a baseball infield and the heaviest self-powered land vehicle on Earth. The CT-2 can move up to 18 million pounds traveling at about 1 mph.
It takes about 12 hours to complete the 4-mile journey between the VAB and the pad. NASA plans to begin the rollout on Thursday.
The space agency completed four WDRs ahead of Artemis I, which contended with hydrogen leaks similar to the Artemis II SLS. Before it launched, teams similarly encountered an issue with the flow of helium to the rocket’s upper stage.