The hazards that the Artemis II crew must navigate during their 10-day flight are plentiful, starting from the second they launch aboard the most powerful rocket to ever carry humans and continuing all the way through their return to Earth nestled inside the Orion capsule.
Many threats the crew will face are obvious, but not all of them are. Take, for example, radiation, which with moderate exposures can increase an astronaut’s long-term risk of cancer and with heavy doses can cause acute sickness. The Artemis II crew will be the first humans in decades to travel beyond low-Earth orbit, fully discarding the protection of Earth’s magnetic field. And while most aspects of cosmic radiation are straightforward to plan for, the outlier is space weather.
So far, Artemis II’s space weather forecast looks clear. “Right now, we’re not keeping an eye on anything,” Lori Glaze, NASA’s acting associate administrator for exploration systems development, told reporters during a press briefing held on March 29, three days before the mission’s next launch attempt. But NASA is loath to simply hope for the best when astronauts’ health is at stake.
On supporting science journalism
If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
And rightfully so—just hours after Glaze’s remark, the sun unleashed an X-class solar flare, the most powerful type known. Such flares are dangerous not only because of their radiation but also because of their tendency to precede coronal mass ejections (CMEs)—immense stellar outbursts of electronics-frying, cell-damaging clouds of charged plasma particles. This flare was no exception, being followed by a fast-moving CME. The CME is expected to at least graze Earth, triggering a moderate geomagnetic storm watch on March 31, with a minor watch continuing into the coming days. NASA does not anticipate any effects on the Artemis II mission, currently targeting launch on April 1 at 6:24 P.M. EDT, but the event is a timely reminder of why radiation monitoring and space weather awareness are key aspects of the flight.
Breaking Down Radiation
Artemis II’s journey will expose the crew members—NASA astronauts Reid Wiseman, Victor Glover and Christina Koch and Canadian Space Agency astronaut Jeremy Hansen—to three different kinds of radiation: the galactic cosmic rays that ricochet through all of space, the protons and electrons magnetically trapped in the two Van Allen Belts that ring Earth and the so-called solar energetic particles that emanate from our sun.
But unlike the easily predictable radiation exposures from flying through the Van Allen Belts or basking in the background flux of galactic cosmic rays, the dose an astronaut gets from solar activity can vary enormously. Predicting space weather remains a decidedly inexact science, comparable to weather forecasting decades ago on Earth. Risks are higher during periods of greater solar activity, which follows an 11-year cycle that researchers track by tallying the dark sunspots that represent magnetic storms capable of producing outbursts.
Right now, the sun is finally moving out of several years of solar maximum—but as this week’s outbursts show, our star is not yet quiet. “Things are still active. It’s kind of a roller-coaster ride at this point,” Shawn Dahl, a forecaster at the National Oceanic and Atmospheric Administration’s (NOAA) Space Weather Prediction Center who is part of a team consulting with NASA on radiation risks, told Scientific American in early March. “We don’t know what to anticipate when Artemis finally goes up.”
All Eyes on the Sun
Not all space weather is a threat—plenty of activity streams off the sun away from Earth’s neighborhood, for example. And the material also matters; what’s of most risk to astronauts is showers of high-energy protons and ions that can tear through metal and flesh alike, damaging DNA and other delicate cellular machinery. Typically, these showers are linked to CMEs, which can push material ahead of them at high speeds. But even CMEs are not automatically a danger: plenty of this material never gains enough energy to threaten astronauts.
“The types of events that we’re concerned about are in the top 10 or 5 percent of all of the events that have been observed in the space era,” says Ricky Egeland, a solar physicist at NASA’s Johnson Space Center. “Those are exceedingly rare events.”
During the current solar cycle, only two incidents of inclement space weather have occurred that would have potentially caused problems for a deep-space mission like Artemis II, says Shaowen Hu, an expert in biological modeling of radiation exposure at KBR, a contractor to NASA’s Johnson Space Center. And even those would have merely prompted concerns, not an emergency response from NASA, he says.
One reason for that is because the Artemis crew capsule, Orion, is designed to protect astronauts from space radiation—much more so than the previous spacecraft that carried humans to the moon. That the Apollo program saw no space weather mishaps is largely a result of luck—a massive solar storm in August 1972, right between the Apollo 16 and Apollo 17 missions, would have posed grave hazards for any astronauts in deep space at the time. “We have come a long way from the Apollo era in terms of being able to protect the astronauts,” says Azita Valinia, an astrophysicist and former chief scientist at NASA’s Engineering and Safety Center. “Spacecraft shielding is a lot more advanced.”
NASA, of course, has a contingency plan for especially potent solar outbursts that could overwhelm Orion’s shielding. Within 30 minutes of an alert, a crew can construct a “shelter,” as NASA calls it—moving bulky items out of stowage to line the capsule’s least-shielded walls. Even if the sun stays quiet through the flight, the Artemis II crew will conduct a shelter-building dry run on day 8 of the mission.
Apollo’s Legacy, Artemis’s Future
Besides having better crew capsule shielding, NASA also now has much better situational awareness, thanks to a modest-but-growing fleet of sun-monitoring spacecraft, improved computer simulations of space weather and reams of biomedical data.
“Back in the Apollo era, we were aware of the problems, and the problems are still the same,” says Hazel Bain, a research scientist at NOAA’s Space Weather Prediction Center. “We’re just armed with better observations and better models now than we were back then.” The observation campaign stretches all the way to Mars, where the Perseverance rover is keeping an eye on side of the sun we can’t see from Earth, and it includes NOAA’s brand-new Space Weather Observations at L1 to Advance Readiness (SOLAR-1) spacecraft, which is still concluding its commissioning period but able to send observations to inform the Artemis II mission.
Although humans haven’t left Earth’s orbit since Apollo, NASA still has more recent uncrewed spaceflight experience to draw on. Most notably, the Orion capsule of 2022’s Artemis I mission was outfitted with more than 5,600 radiation sensors, including some placed within two manikins to measure what astronauts might experience.
The data all those sensors generated matched what NASA experts expected to see. “We found that our models did a very good job of reflecting the environment within the vehicle during Artemis I,” says Janet Barzilla, a bioengineer at Leidos, a contractor to NASA’s Johnson Space Center. “That gave us a lot of confidence as to our approach for Artemis II.”
And space radiation concerns stretch far beyond the Artemis II mission. NASA’s recent replanning of the Artemis program means that next year’s Artemis III mission will no longer leave Earth orbit, but by 2028 the agency intends its Artemis IV mission to land humans on the moon. Here, solar activity will be even more dangerous, Valinia notes, because there’s no Orion shielding at all—and NASA’s much-hyped moon base will be as yet unbuilt. “They’ll only have their space suit as a shelter,” she says.
Editor’s Note (3/31/26): This article was edited after posting to correct the description of the coronal mass ejection that followed an X-class solar flare in late March.