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Astronauts have been venturing into space for 61 years to unlock the human potential for exploration.

But the floating freedom offered by a lack of gravity also presents a number of limits when it comes to the human body and mind.

Short trips to space from the early Mercury and Apollo missions have turned into stays of six months or longer aboard the International Space Station. The floating laboratory has served as an ideal backdrop for scientists trying to understand what truly happens to every aspect of the human body in the space environment -- radiation, lack of gravity and all.

Many of those effects have been well documented over time, especially during the that compared the changes Scott Kelly experienced after a nearly a year in space with those of his twin brother, Mark, who remained on Earth.

Christopher Mason of Weill Cornell Medicine partnered with NASA on this research, and he and Scott Kelly spoke about those findings at the 2022 , a health and wellness event presented in partnership with CNN.

"What was the thing that you missed the most about Earth when you were away for a year?" Mason asked Kelly.

"The weather, of course. The rain, the sun, the wind," Kelly said. "And then I miss people ... that are important to you, you know, your family, your friends."

As NASA plans to return humans to the moon and eventually land on Mars through the Artemis program, there is heightened interest in understanding what effects could be brought on by long-duration travel through deep space.

A big question some scientists have asked is if humans are mentally and emotionally prepared for such a big leap. In short: How will we handle it?

REVEALING RESEARCH

A had participants live for nearly two months in simulated weightlessness by resting in a special bed with their heads tilted down at a 6-degree angle. The tilt creates a headward shift of bodily fluids that astronauts experience in a lack of gravity.

Participants were regularly asked to complete cognitive tests designed for astronauts, relating to memory, risk-taking, emotion recognition and spatial orientation.

Researchers wanted to test if experiencing artificial gravity for 30 minutes per day, either all at once or in five-minute bouts, could prevent negative effects. While the study participants experienced an initial cognitive decline on their tests, it evened out and did not persist for the whole 60 days.

But the speed with which they recognized emotions worsened overall. During tests, they were more likely to see facial expressions as angry, rather than happy or neutral.

"Astronauts on long space missions, very much like our research participants, will spend extended durations in microgravity, confined to a small space with few other astronauts," said study author Mathias Basner, professor in the Department of Psychiatry at the University of Pennsylvania Perelman School of Medicine.

"The astronauts' ability to correctly 'read' each other's emotional expressions will be of paramount importance for effective teamwork and mission success. Our findings suggest that their ability to do this may be impaired over time."

In the study, it was unclear whether this impairment was due to the simulated lack of gravity or the confinement and isolation the participants experienced for 60 days.

A separate 2021 study, published in , developed a mental health checklist based on the stressors faced by astronauts -- which are also shared by those who spend months at research stations in Antarctica.

These two extreme environments -- space and the edge of the world -- create a lack of privacy, altered light and dark cycles, confinement, isolation, monotony and a prolonged separation from family and friends.

University of Houston psychology professor Candice Alfano and her team designed the checklist as a self-reporting method to track these mental health changes. The biggest change people at the two Antarctica stations reported was a decline in positive emotions from the beginning to the end of their nine-month stay with no "bounce back" effect even as they prepared to return home.

The participants also used fewer effective strategies to boost positive emotions.

"Interventions and countermeasures aimed at enhancing positive emotions may, therefore, be critical in reducing psychological risk in extreme settings," Alfano said.

PROTECTING EXPLORERS AWAY FROM HOME

Helping astronauts to maintain their mental sharpness and wellness as they venture far from home is a key goal of . In the past, the program has developed countermeasures to help astronauts combat muscle and bone loss, such as daily workouts on the space station.

Researchers are actively investigating the idea of how meaningful work can bring mission crews together. When astronauts work as a team, whether on the space station or in a simulated Mars environment on Earth, their collaboration is toward a common goal.

And when the work is done, they can spend time together watching movies or enjoying recreational activities to combat feelings of isolation.

However, a mission to Mars, which could take months or years depending on the design of the spacecraft, could lead to feelings of monotony and confinement. And frequent contact with Mission Control and loved ones on Earth will become more disrupted as they get farther from Earth.

"We need to make sure that we have individualized kind of protocols and things for the crew to do," said Alexandra Whitmire, element scientist at the Human Research Program, during a 2021 interview with CNN. "It's really important for us to understand those individuals that will be on that mission."

While some crew members may draw excitement and fulfillment from working on science experiments, others may need to tinker with other tasks. Previous research has already identified , such as self-reliance and problem-solving.

One surprising discovery on the space station is how food -- and the growing of crops -- contributes to better crew morale while maintaining an all-important tangible connection to home.

It's no surprise that and still taste good. But actively growing vegetables has been a rewarding and tasty experience for previous crews on the space station.

Astronauts have reported how fulfilling it was to care for leafy green plants, radishes and and watch the plants flourish, eventually producing an edible bounty.

Human Research Program scientists have questioned if this feeling of fulfillment can be taken a step further. When astronauts such as Scott Kelly or Christina Koch returned to Earth after long spaceflights, they talked about how they couldn't wait to feel rain or ocean waves again.

Guided imagery and virtual reality capabilities may be a necessary part of deep space flights in the future to remind astronauts of their sensory connection to "," even as it shrinks from view.