In this image provided by NASA, the Artemis II crew captured this view of Earth on April 6 as they flew around the Moon.Uncredited/The Associated Press
Scott Solomon teaches ecology, evolutionary biology and scientific communication at Rice University and is a research associate at the Smithsonian Institution’s National Museum of Natural History. His latest book is Becoming Martian: How Living in Space Will Change Our Bodies and Minds.
Now that the Artemis II mission is complete, it is time to consider what is next in space exploration. Artemis III, which will test the ability of the Orion spacecraft to dock with the lunar landers currently being developed, is tentatively scheduled for 2027. If all goes well, Artemis IV will land two astronauts on the moon in 2028 – the first step toward building a lunar base. The long-term vision is to send humans to Mars, which will require building substantial infrastructure there, as well. But with all this focus on testing rockets and spacecraft, it’s easy to lose sight of the most essential component of the Artemis program: people.
Humans have been flying to space for 65 years. Soviet cosmonaut Yuri Gagarin became the first person in space when he flew as the sole crew member on Vostok 1 on April 12, 1961, a trip that lasted 108 minutes and made a nearly complete orbit around the Earth. At the time of his flight, little was known about how the conditions of space affect the human body. A test flight in 1957 involving a dog named Laika demonstrated that space was not immediately lethal, providing Soviet researchers with enough confidence to send a human. But there were still fundamental questions about how basic biological functions would be affected in the absence of gravity. One of Gagarin’s first tasks upon reaching space was to squeeze some food into his mouth from a tube. “Swallowing is possible,” he wrote in his notebook, just before his pencil floated away.
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Much has been learned about how space affects the body since then. Roughly 800 people have been to space, and a total of 28 have now been on or around the moon. The International Space Station has been continuously occupied for the last 26 years, with crews routinely staying there for six months or longer. Several people have been in space for as much as a year, with the record for the longest continuous space mission held by cosmonaut Valeri Polyakov, who spent 437 days on the Russian space station Mir.
An enormous amount of research has been conducted on these men and women, resulting in the emergence of an entirely new field of study: space medicine. Yet when it comes to what people working on a moon base or Martian outpost will experience and how the conditions there will impact them, there are still substantial gaps in our knowledge.
Consider gravity. The weightlessness, or zero-g, of the ISS and spacecraft like the Orion capsule used by the Artemis II crew is different from the partial gravity environment on the moon and Mars. The moon has one-sixth the gravity of Earth, and Mars has about one-third. Being in a weightless environment causes muscles and bones to weaken and causes body fluids to be redistributed throughout the body. Prolonged exposure to microgravity can lead to conditions ranging from anemia to blurred vision. It is unknown whether this will also happen in partial gravity because the longest anyone has spent in these conditions was about three days on the moon.
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Radiation is another factor. In low Earth orbit, where the ISS operates, crews are exposed to as much as 100 times as much radiation as a person on the surface of the Earth. The increased exposure is due to the fact that Earth’s atmosphere blocks some radiation, particularly ultraviolet radiation and cosmic rays. But Earth is also protected from deep space radiation by its magnetic field, which traps energetic particles emitted from the sun and galactic cosmic rays from more distant sources. Because the magnetic field extends beyond low Earth orbit to a region known as the Van Allen radiation belts, the ISS is largely protected from these sources of radiation. The moon, however, is not. It is well beyond the Van Allen radiation belts and lacks its own magnetic field, so people on the surface of the moon are exposed to about two to three times more radiation than crews in low Earth orbit.
Understanding how increased radiation exposure and partial gravity of the moon will affect people is going to be essential for the plans that NASA has outlined for the next decade. Some information is expected to come from science conducted as part of the Artemis II mission. An experiment called AVATAR involved cells collected prior to the mission from the four crew members that were kept alive on a device that flew inside the Orion capsule. By analyzing these cells and comparing them to identical cells that remained on Earth during the mission, any effects caused by radiation exposure should be detectable. Future missions could include similar devices that can help determine human health risks without having to send actual people.
Keeping crews on the moon healthy will also be more challenging than on the ISS because an evacuation from the moon would take longer and be more complex. In January, astronaut Mike Fincke experienced a sudden inability to speak that lasted 20 minutes while aboard the ISS. While NASA has not released information about what caused this condition, they evacuated him and the other three members of his crew a few days later. Had it been an even more urgent emergency, like a heart attack or stroke, they could have had him back on Earth within hours. That would not be possible on a lunar base because it takes about four days to get back to Earth.
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Having people on Mars will be even more challenging. It takes six to nine months to travel between Earth and Mars, but that can only be done when the two planets are close together in their respective orbits, which only happens about every two years. Evacuations will not be possible. The distance makes communication much more complicated, too, because depending on where they are in their orbits, it takes between three minutes and 24 minutes to send a message between the planets. Crews operating on Mars will need to be largely self-sufficient.
Food will be another challenge for people on Mars. To date, all human space missions have relied on sending packaged food that can last for the entire journey, or sending additional stable food on resupply missions (which can include highly coveted fresh produce). Neither is a viable option for the two-and-a-half to three-year duration of a Mars mission. While some food can be sent for the journey and to serve as an emergency backup, crews will need to produce their own food by growing crops. So far plants have only been grown in space on a very small scale, just a few individuals at a time.
But what we will learn about keeping people healthy and well fed on prolonged lunar missions will be very useful for planning for Mars. The gravity on Mars is roughly halfway between that of the moon and Earth. Studying how the moon’s gravity affects the human body should therefore be instructive for keeping people healthy on Mars by, for example, determining how much exercise is necessary to keep muscles and bones strong. Likewise, Mars is similar to the moon in its lack of a magnetic field and has an atmosphere so thin that radiation levels on its surface are similar to that of the moon. Figuring out how to shield crew members from radiation on the moon, for example by tunnelling underground or using existing craters or lava tubes, will be useful practice for establishing a safe base on the red planet. And farming using lunar regolith will give us insights into how we may be able to grow plants on Mars.
This vision for the future will of course require substantial engineering advances to build rockets, landers, and habitats to get people to these outposts and to keep them alive. We will also need rovers, spacesuits, and infrastructure for construction, energy, and communication. But let’s not forget that the most important part of human space exploration is, and always has been, humans.