While LEO affords a great opportunity to study humans in space, it doesn’t answer the question of what happens in deep space. The ISS is about 250 miles (400 kilometers) from Earth’s surface, whereas the Moon is about 240,000 miles (386,000 km) away and Mars an average of 140 million miles (225 million km) from Earth.
Once beyond Earth’s magnetosphere, astronauts in deep space will be exposed to galactic cosmic radiation. “That’s a unique type of radiation we need to think about and what type of damage that would do to tissues,” Fabre says, “whether it be during the mission or long-term effects.”
As humans venture farther from Earth, she continues, we will also need to address how that distance will impact stress levels and mood. “How do we stay engaged in our activities and our workloads so that we have optimal cognitive abilities?” she asks.
NASA notes that a confined environment and elevated levels of stress hormones lead to a weakened immune system. This, Fabre says, leads in turn to metabolism issues: “The microbiome [also] plays a big role in our metabolism. How we break down nutrients and the type of nutrients or the type of molecules that we get from our microbiome impacts the rest of our tissue or physiological function.”
Then there is the changing gravitational landscape: Astronauts would go from Earth’s gravity to weightlessness on each three-month trip to and from Mars, then switch to Mars’ gravitational tug, which is about one-third of Earth’s. Anyone who returns to Earth would experience the situation in reverse. These transitions will certainly take a toll on the body, including issues with coordination, orientation, and even movement. This is also why some people experience motion sickness in space.
Fortunately, there are several analogs available on Earth to study the effects of these hazards. NASA’s Human Exploration Research Analog, or HERA, at the Johnson Space Center, is a three-story habitat used to simulate the isolation and close quarters that might be experienced by future long-term space explorers. Researchers also turn to studies of people who spend time working in Antarctica to examine the effects of isolation.
The NASA Space Radiation Laboratory in Brookhaven, New York, conducts studies on the effects of radiation on living tissues. “[The lab] can simulate, to some extent, some of the galactic cosmic radiation particles that we would be exposed to,” Fabre says, “[so] that we can start to understand some of the damage unique to these types of radiation.”
TRISH is using advanced tools called complex in vitro models (CIVMs) to understand how tissues fare in the presence of cosmic radiation. CIVMs include artificially engineered 3D cell cultures, organs-on-chips, and bioprinted tissues, which are analogous to anatomical and physiological aspects of human biology. In the long term, TRISH plans to send diverse cell samples on the Moon to model a broad range of human traits, such as sex, gender, and ethnicity. The idea, Fabre says, “is to understand what is it that [an individual] might be more susceptible to … so in the event that [a] medical event would happen, you have the right interventions to take so you can complete your mission and still maintain health and mental performance.”
After all, millions of miles from Earth, going back home for a sick day is not an option.