When NASA’s Artemis II mission made history by launching on April 1, 2026 — the first crewed lunar voyage in more than five decades — the world watched with awe as humanity’s next great leap unfolded. After years of planning, technological development, and scientific preparation, four astronauts — Reid Wiseman, Victor Glover, Christina Koch, and Jeremy Hansen — soared into space aboard the Orion spacecraft, headed for the Moon. The excitement was palpable, and space enthusiasts around the globe celebrated the continuation of a journey that first began in the 1960s and 1970s during the Apollo era.

Even so, while the mission marked a triumph for space exploration, it also carried with it inherent risks that scientists, engineers, and astronauts themselves have acknowledged. No journey beyond Earth’s protective atmosphere is without peril. Among the multitude of potential challenges — from life support reliability to navigation accuracy and system failures — one concern has stood out to veteran astronauts and experts alike as especially significant.

That concern, according to seasoned space veteran and former NASA astronaut Mike Fincke, isn’t the kind most people immediately think of when they imagine lunar missions. It isn’t about the rocket’s power, the spacecraft’s design, or even the psychological strain of leaving Earth for the first time. Instead, Fincke has underscored a challenge that is subtle, persistent, and deeply connected to human physiology: the long‑term effects of radiation exposure on the human body while traveling beyond low‑Earth orbit.

In an exclusive interview following the launch, Fincke discussed why this concern is not just theoretical — but deeply grounded in decades of space science and planetary research. His insights give us a clearer understanding of why Artemis II is not merely a moment of celebration but also an essential step in identifying and solving one of spaceflight’s most stubborn mysteries.

Radiation: The Invisible Threat No One Can See

When astronauts leave Earth’s atmosphere, they also leave behind the protective blanket of the planet’s magnetic field — a shield that blocks much of the harmful radiation emitted by the sun and cosmic sources. In low‑Earth orbit — where the International Space Station operates — this magnetic field still offers substantial protection. But once spacecraft travel beyond this boundary, as Artemis II did on its way to the Moon, that layer of defense disappears.

“With Artemis II, we are essentially entering what we call ‘deep space,’” Fincke explained. “Deep space doesn’t have the kind of protection our atmosphere and magnetic field provide. That means astronauts are exposed to higher levels of ionizing radiation, and that exposure can have effects we don’t fully understand yet.”

Radiation comes from multiple sources: solar flares, galactic cosmic rays, and other high‑energy particles moving through the universe at near light speed. On Earth, we’re largely shielded from these particles, and even on the International Space Station, astronauts experience only a fraction of the levels that will be encountered in deep space.

The concern is not simply that radiation levels are higher — it’s that the human body has limited defenses against many forms of energetic radiation. Over time, exposure can damage DNA, contribute to cancer risk, and affect neurological functions. Early studies of astronauts who have spent extended periods in space show a range of impacts, including changes to vision and balance, as well as cellular changes that could carry long‑term consequences.

In the context of Artemis II — a mission expected to last around ten days — radiation levels are not anticipated to reach truly dangerous thresholds. But Fincke emphasized that even short missions matter.

“What Artemis II gives us is a real human data point,” he said. “We’ve sent probes and uncrewed missions through deep space before, but there’s nothing quite like actually having a human body in that environment. Every piece of data we collect contributes to future missions — especially those that might go to Mars.”

The Uncertainty of Space Radiation Effects

One of the reasons radiation tops the list of concerns is that its effects are not entirely predictable. Medical science has decades of experience understanding radiation exposure on Earth — in contexts like X‑rays, nuclear exposure, and certain medical treatments — but space radiation is different. The particles involved are typically more energetic and more deeply penetrating than those encountered on Earth.

Dr. Sheila Patel, a space medicine researcher, has described cosmic radiation as “a kind of relentless drizzle of high‑energy particles that our bodies have never evolved to handle.” While the intensity is often low on a day‑to‑day basis, the cumulative impact over weeks, months, or years could be profound.

“Our models can estimate risk,” she explained in a recent journal interview, “but until we have long‑duration human data outside Earth’s magnetic field, we can’t be certain of all the consequences. That’s what makes missions like Artemis II so important — it’s not just a lunar mission, it’s a living laboratory.”

In other words, space agencies are using Artemis II not only to test technology and human endurance but also to gather crucial biological data that could help scientists protect future astronauts on longer missions.

For example, radiation can break molecular bonds in cells, potentially leading to cell death or mutations. The body may be able to repair some levels of damage, but sustained exposure could overwhelm those mechanisms. There are also concerns about the impact on brain cells, cardiovascular health, and reproductive cells — a comprehensive list that still carries many unknowns.

Microgravity and Radiation: A Compounding Challenge

Radiation isn’t the only thing astronauts must contend with in space. Microgravity — the absence of gravity — itself causes a host of physiological changes. Muscles weaken, bones lose density, and fluids redistribute toward the head. The combination of microgravity and radiation exposure creates a dual challenge that space medicine experts refer to as a “synergistic stress.”

Fincke touched on this during our conversation: “When you remove gravity, the body starts adapting in ways that aren’t always good over time. Simultaneously, the lack of shielding makes you more vulnerable to particles that can damage cells. On short missions like Artemis II, these changes are minimal and manageable. But for future deep space missions, that’s where it becomes a real concern.”

This interplay makes Artemis II not only a technological mission but a scientific one. The data coming back from the crew — both qualitative and physiological — will be invaluable in planning longer expeditions, including potential human missions to Mars, which could last months or even years.

Engineering Solutions vs. Biological Reality

NASA and partner organizations have long recognized radiation as a barrier to deep space exploration. Over the decades, engineers have developed shielding materials, radiation detectors, and protective strategies to help mitigate exposure. Some spacecraft designs incorporate specialized materials woven with hydrogen or polyethylene, both of which can help absorb or deflect certain types of radiation.

However, shielding is not a perfect solution. High‑energy particles can pass through most materials with ease, and heavy shielding adds significant weight — a critical consideration when launching spacecraft. The engineering challenge becomes one of balance: how much protection can be realistically integrated without compromising mission performance?

That’s where biological countermeasures come into play. Scientists are exploring pharmaceuticals that enhance DNA repair mechanisms or antioxidants that help protect cells from radiation‑induced stress. Research is even underway into genetic factors that might influence individual susceptibility to radiation.

“We’re not just asking, ‘How do we build a better shield?’” Fincke explained. “We’re also asking, ‘How do we make the human body more resilient to this environment?’ That’s the frontier of space medicine.”

Artemis II, while not a long‑duration mission, will collect medical and biological data that helps answer these questions. Tests performed on the astronauts’ blood, tissues, and metabolism will feed into models used to prepare for longer missions. This is why Fincke describes the radiation concern as both serious and strategic: it’s not an immediate threat on Artemis II, but a central one for the future of human space exploration.

The Human Side of Risk

One of the most profound aspects of the Artemis II mission is the fact that real human beings are living inside the very questions scientists are trying to solve. For all the robotic probes, simulations, and test data, nothing compares to actual human biology in real space conditions.

Astronauts on Artemis II are collecting observations, participating in experiments, and reporting sensations that no machine could. The data they generate is already contributing to humanity’s understanding of life beyond Earth.

But there’s also a human story behind every reading and measurement — the emotional, psychological experience of leaving Earth for the first time.

Fincke spoke of this poignantly: “We talk a lot about the physical challenges, but the psychological impact of being this far from home — the first humans in over fifty years — is another layer entirely. The radiation concern is scientific. The emotional weight is human. The combination is what makes human spaceflight both terrifying and extraordinary.”

The astronauts, aware of the hazards, prepare rigorously before launch — not only physically, but mentally. They know they are pioneers in an environment that few have experienced. They take part in training that simulates isolation, communication delays, and the effects of distance from Earth. They practice emergency procedures and life support troubleshooting. Every step is designed to ensure safety and preparedness.

Yet radiation remains one variable that cannot be fully rehearsed on Earth. Only in space can its effects be directly observed.

What Artemis II Data Could Reveal

Already, scientists are analyzing early biomarkers and readings from the crew’s health monitoring systems. Some of the areas of interest include:

Blood markers of cellular stress – tracking how radiation may affect DNA repair and immune function.
Neurocognitive performance – observing whether radiation affects reaction time, memory, or sensory processing.
Cardiovascular metrics – assessing how prolonged travel in microgravity impacts heart function alongside radiation exposure.
Sleep patterns and circadian rhythms – radiation and microgravity both affect sleep cycles, and combined effects are an important research focus.

This data not only informs Artemis II but lays the groundwork for Artemis III and beyond. Future missions will carry humans deeper into space, potentially to Mars and back. These missions will last months or years, and the radiation exposure will be significantly greater than what Artemis II experiences.

Understanding how even short exposure affects human biology is essential if astronauts will one day live, work, and perhaps even raise families off Earth.

Balancing Risk With Exploration

The radiation challenge, while serious, is not a reason to halt human exploration. Instead, it’s a reminder of why exploration requires courage, preparation, and collective scientific resolve.

NASA and its partners continue to advance materials science, medical research, and spacecraft design to mitigate risks. Meanwhile, missions like Artemis II build the empirical data necessary to refine predictions, improve countermeasures, and protect astronauts on longer journeys.

Fincke’s perspective — that radiation exposure is the most significant concern — is grounded not in fear, but in scientific realism.

“It’s not that radiation will stop exploration,” he said. “It’s that understanding it is the key to expanding our reach. The more we know, the safer we can make long‑duration missions. Artemis II is a step toward that knowledge.”

Looking Toward the Future

As Artemis II continues its lunar trajectory, scientists and space enthusiasts watch closely. Every heartbeat, every measurement, and every report helps paint a clearer picture of human resilience in space.

The mission represents more than a historic moment; it represents the beginning of a new era of discovery — one where data drives decisions, and human courage interacts with unknown environments.

Fincke’s concern about radiation is an invitation not to fear, but to study, prepare, and innovate.

In his words: “Space doesn’t require perfection. It requires persistence.”

And with Artemis II, humanity is persisting — one measured flight, one data point, and one courageous step at a time.