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Not too long ago, most human beings who journeyed into space were career astronauts — rigorously trained professionals, screened and prepared to leave Earth’s atmosphere at great speeds atop enormous rockets.

Today, more civilians are making that trip with companies like Elon Musk’s SpaceX, which plans to send people to Mars someday.

But as space tourism heats up, what does “fit for flight” really mean for people who are not trained astronauts?

“We probably can’t use the same criteria we use for career astronauts because these [civilian] trips are going to be relatively short,” said Dr. Mathias Basner, a psychiatry professor at the University of Pennsylvania School of Medicine. “The criteria can probably be somewhat relaxed. The question is, to what degree?”

That’s what Penn medical researchers like Basner and others worldwide are trying to figure out by studying the physical and mental health effects of spaceflight among average people.

Penn researchers and other scientists published their findings in 44 papers this week in the journal Nature. The data is part of a larger research initiative with the Translational Research Institute for Space Health (TRISH) and NASA.

“Our everyday functioning is comprised of all of these different functions of the brain that work simultaneously,” Basner said. “So we try to learn, which of these are actually most affected by spaceflight and what could it mean?”

In 2021, scientists got a new opportunity to study this when four people made history and became the world’s first all-civilian team to go into space and orbit Earth multiple times before returning to the planet’s surface.

The SpaceX Inspiration4 mission included a billionaire entrepreneur and pilot, a cancer survivor and physician assistant, a data engineer and Air Force veteran, and a geoscientist and professor.

During their three-day trip, crew members recorded some of their physiological and mental health stats like heart rate, oxygen level, mood state, sleep quality, alertness and other metrics by running a series of neurocognitive tests and using Apple watches and non-invasive medical equipment.

Researchers took that data and studied different areas of health outcomes and changes. Basner and his team at Penn focused on how spaceflight affected cognition, behavior and psychological performance.

“So we’re looking at things like attention, memory, learning, risk-taking or emotional recognition,” Basner said. “Are you still able to interpret somebody who is emoting anger or fear or happiness? This is all very important and relevant for spaceflight spatial orientation.”

The team found that some crew members experienced cognitive decline and issues in several categories during the early phase of flight, but the effects were temporary. All fully recovered later in the flight or shortly after returning to Earth.

“Those transitional phases are really critical, where all of a sudden, oh, you’re in microgravity and your brain has to rethink how it’s interpreting those signals,” Basner said. “There are a lot of changes that can affect your performance. This is what we saw.”

Christopher Jones, an assistant professor of psychiatry at Penn, said the effects varied greatly from person to person, which led to even more research questions.

“Is there an individual phenotype or something that we can help define and understand so we could potentially know how somebody with this makeup may respond to the spaceflight environment?” Jones said. “Are they going to be resilient or may they be vulnerable to some of the effects?”

The findings and data can be used to better inform safety protocols for everyday people who want to travel to space, Basner said. It also can be used to set expectations for travelers who ultimately want to enjoy their time in space for the short time they are there.

“The first few days in spaceflight can be pretty miserable, right?” he said. “We want to learn who is susceptible to that and also what we can do to mitigate those things in terms of medication or something you can do on the ground to prepare you for that period, because you want to enjoy it.”

Researchers from all over the country are working with the Translational Research Institute for Space Health to build a database of information and health outcomes of civilian space travelers. The goal is to one day make it accessible to other scientists and experts around the world as space tourism continues to grow.