After a grueling descent through Earth's atmosphere, NASA will strap the Artemis II astronauts into bulky spacesuits for an obstacle course.

Within mere hours of the Orion spacecraft's splashdown on Friday, April 10, the crew — Commander Reid Wiseman, Christina Koch, Victor Glover, and Jeremy Hansen — won't be afforded much time to rest and relax. Instead, the four will be bounced around from one research group to the next before they've fully acclimated to Earth gravity. 

One of those studies will include putting their "right stuff" to the test. The gauntlet, far less flashy than an episode of American Gladiators, will unfold back at NASA's Johnson Space Center in Houston. There, a giant robotic crane and a heavy test suit will help a small team answer a crucial question: After 10 days of weightlessness in space, how soon can humans safely get back to work in another world?

The experiment grows out of a longer‑running study with astronauts returning from six‑month missions on the International Space Station. Those crews spend about as long in orbit as a trip to Mars might take — and they come home pallid and wobbly. 

Scientists worry that in a weakened state, astronauts might not be ready for moonwalks or Marswalks, which require strength and agility.

"We don't want to put the astronauts in a position where they’re going to be stranded in a spacesuit, asking them to do tasks that are probably above what their physiologic capabilities are going to be in," said Jason Norcross, a senior scientist leading the effort. "This helps us really with planning, more than anything else."

Without gravity, muscles atrophy and aerobic fitness fades. The brain and inner ear systems that tell us which way is up and help us stay balanced also need time to readjust. 

To investigate that, Norcross' team has used the Active Response Gravity Offload System, or ARGOS, at Johnson. Picture a crane that holds part of a person's weight. By lifting just the right amount, ARGOS lets a suited astronaut feel as if he or she is in a different gravity environment.

For space station astronauts, ARGOS is tuned to Martian gravity, and the obstacle course is framed with that in mind: Can someone who has spent six months in orbit step into a 400‑pound suit and, within about a day of landing, safely make their way through a mock Mars spacewalk? 

Faking lunar gravity

For Artemis II, the team will reuse the same basic setup but dial ARGOS to lunar gravity instead — one‑sixth Earth's pull — and tweak the tasks to echo the type of work astronauts will need to do on the moon.

Within one to four hours of landing, the Artemis II astronauts will first tackle a capsule escape drill using a mock spacecraft. Lying on their backs, they'll have to sit up, deploy a ladder, climb up and over it, shoulder a pack, and walk a set distance. This exercise seeks to understand whether a crew can open a hatch if a landing goes awry. 

That's a question shared by many space physiologists, said Marie Mortreux, an assistant professor at the University of Rhode Island. She studies how muscles and bones cope with different levels of gravity.

"When they come back home from space, you're familiar with those images," said Mortreux, who isn't involved in the Artemis II EVA simulations. "They can't walk … and I'm like, 'What's going to happen if they can't make it out?'"

Mortreux's research in rodents suggests that lower-body, weight‑bearing muscles take the biggest hit in space. Arm muscles — the ones people need for latches and handles — hold up better because astronauts use them constantly to pull themselves around in weightlessness. That's reassuring, she told Mashable, but it's not a reason to be complacent, underscoring the need for more research like this. 

Despite being tired and uncomfortable, all space station astronauts who have been subjected to the experiments so far have managed to complete them. 

Inside the spacesuit challenge

The test will continue with a simulated lunar EVA in moonlike gravity the next day. Each of the four crewmates will change into liquid cooling garments, close‑fitting layers threaded with thin water tubes to keep them from overheating. Then, they'll climb into heavy-duty EVA spacesuits that require entering through a back hatch. Just getting into them is physically taxing. 

Once the astronauts stand up, the team will connect their suits to ARGOS. From that point forward, the test compresses the most challenging parts of a moonwalk into a 30 to 40‑minute obstacle course: down a ladder on a mock lander platform, across unstable ground, through geology drills, and onto a steep treadmill hike. The ladder is deceptively difficult: Any task that forces crew to turn their heads, look down, or rely on their inner sense of orientation, could trigger vertigo.

"You'll often see [returning astronauts] keep their head in line with their body," Norcross said, "which is why, when we've designed a lot of our tasks, we've designed them with a lot of turning, a lot of head movement up and down."

Next, the astronauts will have to bend and squat through tasks meant to rehearse making electrical and fluid connections. In a real mission, that kind of work might power up a lander or connect life‑support lines — unglamorous but essential chores.

From there, the experiment will shift to the most punishing part. In a trailer filled with sand and rocks, the astronauts will carry several 30‑pound bags back and forth over uneven footing. The ground tends to shift, visibility is limited by the helmet, and the suit resists every stride. 

Then, for the science activity: The astronauts will have to hold a tool steady for about a minute to mimic using an instrument, swing a hammer to chip off a rock fragment, and dig a trench with a scoop. Those moves echo what future crews might need to do to collect samples on the lunar surface.

The test will finish on a treadmill. Still attached to the crane, the astronauts will walk roughly half a mile over slopes, including a steep uphill climb. 

"Most treadmills don't even go up to 20 percent," Norcross said, explaining how high they'll set the inclination, "and sometimes it requires them to slow down pretty significantly. But they still put one foot in front of the other."

A safety check for future moonwalks

Each Artemis II astronaut will endure the obstacle course, which will take about 1.5 hours to complete, one at a time. Norcross' team will track how long each task takes, how much energy the astronauts use, and how their heart rates respond. The whole experiment repeats three days later to measure how their performance changes over time.

From the space station study, Norcross already sees a pattern: Astronauts look and feel far better by the fourth day after landing, and close to normal within a week, even after half a year in orbit. 

Because Artemis II was short, these tests give NASA a cautious baseline. The data should help mission planners decide how aggressive to make the first lunar excursions, how far to let astronauts roam, and which jobs to push to later days after their bodies have had time to adapt. 

So even though the Wiseman, Koch, Glover, and Hansen didn't set foot on the moon, they're going to at least feel like they did.

"For this Artemis II crew, it'll be, 'Congratulations, you've done your lunar EVA,'" Norcross said.