NASA is updating the way it monitors astronaut health during spaceflight, a shift that could reshape how space agencies keep crews safe on longer journeys beyond Earth.
Later today, four crew members are expected to plunge back through Earth’s atmosphere, returning at roughly 25,000mph in what will look like a blazing descent as they wrap up a mission tied to the Moon, coming about 50 years after the last comparable era of lunar exploration.
While the flight differs from past missions in plenty of ways — including not actually landing on the Moon — it also featured a new kind of science and biomedical tracking that NASA says has never been carried out in quite this way before.
After the re-entry capsule is scheduled to splash down shortly after 8pm EST in waters off San Diego, the Artemis II team will have delivered new data about how human biology responds to deep-space conditions, potentially informing future health and safety upgrades for exploration missions.
Orion launched on April 1 carrying NASA astronauts Reid Wiseman, Victor Glover and Christina Koch, along with Canadian Space Agency astronaut Jeremy Hansen. But they also brought “passengers” of a very different kind.
Those additional travelers weren’t full people, but tiny biological stand-ins: USB-sized “avatars” made using samples of the astronauts’ bone marrow. The idea is to observe how human tissues may change when exposed to deep-space stressors.
NASA refers to the technology as organ-on-a-chip systems, designed to replicate aspects of organ function so researchers can watch how microgravity and higher radiation levels might affect the body during long-duration missions.
This, says Lisa Carnell, Director of NASA’s Biological and Physical Sciences Division, is something that ‘we’ve never done’ before, and could lead us to ‘learn something new’ about how bodies react to being outside of Earth.
The space agency’s site explained: “NASA’s organ chip research will study how different space stressors affect tissue before sending the first humans —Americans — to Mars. It could provide valuable information for developing measures to protect astronaut health on their journeys, such as personalized medical kits.”
Alongside the organ-chip work, the crew has also been providing saliva samples so scientists can compare results from before, during, and after the mission.
In other words, this is part of a broader push to capture more detailed biological data than ever before — and to turn that information into practical countermeasures for future explorers.
“When we send these alongside Christina, Victor, Reid, Jeremy, they all may respond different to the deep space radiation environment. Somebody may be radio resistant and will learn something new, and you know, or maybe somebody is more extremely susceptible to radiation,” Carnell said, per CNN. “Well, now we can tailor medical kits that we can make personal lives for them on their journey. They go to Mars, they go to the moon, to live for long duration. We can send the right therapeutics with them to make sure they stay healthy and that they can thrive in those environments.”
Carnell also suggested the avatars could potentially be sent ahead on earlier flights, offering a way to spot possible red flags before crews ever depart.
“In the Apollo days, it was just a few days on the surface. If we’re literally going to have people on the surface for a long period of time, even 30 days or longer, I mean, we don’t have data on that at all, right?” Carnell said. “We like to say, ‘Know before we go.’ It’s that simple. Like, how do we know before we send them to ensure that we bring them back healthy and that they’re as safe as can be? And this is such a simple … eloquent way to do that.”
Once Orion returns, helping Wiseman, Glover, Koch and Hansen safely out of the spacecraft will be a coordinated effort involving NASA and the US Department of Defense.
After splashdown, four helicopters are expected to circle the capsule — two for recovery operations and two focused on capturing images, according to Florida Today.
A stabilizing collar will be lowered to keep Orion properly oriented in the water, and then a recovery basket will be used to lift each astronaut out one by one.
From there, the crew will be taken to the nearby naval vessel USS John P. Murtha for medical evaluations before being transported back to Houston.
Even though Artemis II is a comparatively short spaceflight — especially when compared with extended stays such as Suni Williams and Butch Wilmore spending 608 days away from Earth across 2024 and 2025 — time in microgravity can still change the body quickly.
Kevin Fong, founder of the Centre for Altitude, Space and Extreme Environment Medicine at University College London, told the BBC: “In some experiments with rats, they’ve seen up to a third of muscle from particular muscle groups being lost within seven to 10 days of flight – that’s a huge, huge loss.”
To limit muscle loss, the Artemis II schedule includes exercise using a compact device known as a flywheel.
Because Orion’s volume is only 316 cubic feet — around the size of a small bedroom, according to NPR — fitness gear has to be efficient and space-saving. The flywheel is often compared to a multipurpose rowing machine because it can support multiple kinds of resistance movement.
Jeremy Hansen explained before launch: “We can change the dynamics of this device so that we can do weightlifting with it. So we can do squats. We can do dead lifts. We can do curls. We can do high pulls.”
The challenges don’t stop at muscle. Returning astronauts often describe balance problems as their bodies readapt to gravity.
NASA astronaut Jasmin Moghbeli, who returned to Earth in 2024 after 200 days in space, said: “With eyes closed, it was almost impossible to walk in a straight line.”
That’s largely because the inner-ear system that helps humans balance on Earth behaves differently in microgravity, and it can take time to “recalibrate” after landing.
ESA astronaut Andreas Mogensen, who was on the same mission, said: “I felt wobbly for the first two days. My neck was very tired from holding up my head.”
And for some astronauts, the biggest adjustment is simply feeling weight again.
While NASA’s Jeanette Epps, who spent 235 days in space and returned in October 2024, said the main thing that took some getting used to was the heaviness of Earth.
She said: “You have to move and exercise every day, regardless of how exhausted you feel.”