Human body in space

For over six decades, NASA and other space agencies have launched some of humanity’s most elite individuals into space—not just scientists and doctors, but also athletes like national cycling champions and marathon runners. Thanks to these top-performing astronauts, we've learned a lot about how space affects the human body at its physical peak.

But what about the average person? What happens to someone whose most intense endurance feat is binge-watching Avatar: The Last Airbender over a weekend?

Until recently, the answer was out of reach. The high costs of spaceflight and rigorous selection criteria made it nearly impossible to study how space impacts the general population—until 2021. That year, the Inspiration4 mission sent four civilians into orbit for three days, confined to a spacecraft about the size of a cargo van. Now, research from that mission is beginning to emerge.

This unique opportunity offered valuable data: not just about how an “average” human body copes with spaceflight, but also about how non-professional astronauts can help expand our understanding of space health. More participants mean more data—and that's always a win for science.

Even though NASA astronauts remain highly trained professionals, missions like Inspiration4 also benefit the agency. NASA still needs answers to major questions before long-duration missions to Mars become reality. For instance: How will astronauts monitor their own health? What kinds of medical tests can they realistically perform on each other, far from Earth?

Civilian missions are ideal for exploring these questions. NASA astronauts take years to train and are in limited supply, but civilians can help test new health-monitoring systems under real space conditions. Inspiration4 enabled organizations like the Translational Research Institute for Space Health (TRISH) to conduct meaningful experiments.

During the mission, each crew member wore an Apple Watch to track heart rate, activity levels, and oxygen saturation. They used an iPad to log mood surveys and complete cognitive assessments, similar to those performed on the International Space Station (ISS). They also used compact, smartphone-connected ultrasound machines to scan each other’s eyes, bladders, and veins—looking for early signs of common space-related health issues. To evaluate immune response, they collected blood and skin samples, both in space and back on Earth.

By comparing pre-, in-, and post-flight data, researchers could work around the study's small sample size and still gather meaningful insights. While science takes time, the first results from Inspiration4 were published in 2024.

The findings were encouraging: None of the civilian astronauts experienced serious health issues. This suggests that short-duration spaceflights may not pose major risks to the general population. One particularly good sign: unlike long-duration missions that often result in blood clots, scans of the civilians' neck veins revealed no such issues.

Another area of study involved space motion sickness. Researchers explored whether pre-flight eye alignment could predict susceptibility to nausea. Interestingly, two astronauts showed a noticeable shift in eye alignment post-flight—these were also the two who did not get sick. This suggests that ocular asymmetry might influence how well someone adjusts to microgravity, which could eventually inform astronaut selection or medication planning.

Beyond motion sickness, civilian astronauts experienced well-documented physiological changes seen in professionals. For example, their telomeres—the protective caps on DNA—lengthened in space, only to shrink rapidly upon return. This fluctuation may make DNA more prone to mutations. Reactivation of dormant viruses like mono and chickenpox also remains a concern, especially on longer missions.

Cognitive performance was another area of interest. Civilian astronauts performed worse than their NASA counterparts on in-space cognitive tests, though they returned to normal after landing. This dip might reflect an early adaptation period to microgravity. Since NASA typically starts testing astronauts several days after they reach the ISS, it’s possible early cognitive impacts have gone unnoticed until now.

One of the most exciting outcomes? Nearly all health data collected by the civilians—including ultrasounds and cognitive assessments—was usable, despite no real-time help from ground control. This is a major step forward. On missions to Mars, for instance, communication delays of up to 23 minutes will make live support unrealistic. Inspiration4 showed that minimally trained astronauts could successfully collect critical health data on their own.

The success of Inspiration4 marked the beginning of a new era in civilian space travel. It paved the way for missions like Polaris Dawn, launched on September 10, 2024. That mission studied space radiation by flying through Earth’s radiation belts, and saw two civilians—Jared Isaacman among them—perform a spacewalk for the first time. All four crew members returned safely, adding even more valuable data for TRISH.

With two more Polaris missions already planned, we’re on track to answer even more questions about how spaceflight affects the average human. Like: Will I get chickenpox again? And if I do, will there be enough Wi-Fi onboard to binge-watch Avatar during quarantine?