Space travel presents numerous challenges, not the least of which have to do with astronaut health and safety. And the farther these missions venture from Earth, the more significant they become. Beyond Earth’s protective atmosphere and magnetosphere, there’s the threat of long-term exposure to solar and cosmic radiation. But whereas radiation exposure can be mitigated with proper shielding, there are few strategies available for dealing with the other major hazard: long-term exposure to microgravity.
Aboard the International Space Station (ISS), astronauts rely on a strict regimen of exercise and resistance training to mitigate the physiological effects. These include muscle atrophy, bone density loss, organ function, eyesight, and effects on cardiovascular health, gene expression, and the central nervous system. But as a recent NASA study revealed, long-duration missions to Mars and other locations in deep space will need to be equipped with artificial gravity. This study examined the effects of microgravity on fruit flies aboard the ISS and demonstrated artificial gravity provides partial protection against those changes.
The study was conducted by researchers from the Space Biosciences Division at the NASA Ames Research Center, the COSMIAC Research Center at the University of New Mexico, the Universities Space Research Association (USRA), the Nevada Bioinformatics Center at the University of Nevada, the Blue Marble Space Institute of Science (BMSIS), the Biological and Physical Sciences Division at NASA Headquarters, and multiple universities. The paper that details their findings was published on September 6th in the journal Cell Reports.
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In this study, the team conducted a month-long investigation using the Multi-use Variable-gravity Platform (MVP), a centrifuge-based commercial testbed that arrived on the ISS in 2019. This experiment has distinct compartments and provides flies with fresh food as they live and reproduce. This allowed the team to house different generations of flies separately and under different levels of gravity, with one exposed to microgravity (like their astronaut counterparts aboard the ISS) and another exposed to Earth-like gravity (9.8 m/s2, or 1 g).
The research team then monitored their behavior using cameras embedded in the hardware. At different points, some of the flies were frozen and returned to Earth for analysis to see how the different levels of gravity affected their gene expression and its impact on their nervous systems. As Dr. Janani Iyer, a USRA project scientist at NASA’s Ames Research Center, explained in a recent NASA press release:
“Microgravity poses risks to the central nervous system, suggesting that countermeasures may be needed for long-duration space travel. As we venture back to the Moon and on to Mars, reducing the harmful effects of microgravity will be key to keeping future explorers safe. This study is a step in the right direction to explore the protective effects of artificial gravity in space and to understand the adaptation to Earth conditions after returning from space.”
Fruit flies are the ideal organism for this kind of research because of their similarities to humans in terms of cellular and molecular processes and their short lifespans and reproduction cycles (two months and two weeks, respectively). Almost 75% of the genes that cause disease in humans are shared by fruit flies, meaning changes in their gene expression will resemble possible changes in humans. In addition, the three weeks they spend in space is equivalent to about thirty years of a human’s life, allowing scientists to observe decades worth of biological information in a short amount of time.
Once the experiment was complete, the flies were returned to Earth aboard a SpaceX Dragon capsule and transported to NASA Ames for further analysis. For two days, scientists conducted behavioral and biochemical tests on these “flyonauts,” which consisted of monitoring their movements inside their habitat, cellular changes in their brains, how changes in gene expression affected their nervous systems, and more. They then combined their observations with footage from the MVP cameras and compared the results to a control group that had remained on Earth.
Among the behaviors studied, the scientists examined how the flies climbed the walls of their container – a natural response fruit flies have when tapped down. They found that the flies in microgravity were more active than those exposed to artificial gravity but experienced difficulty during the climbing test upon their return to Earth. The post-flight analysis also revealed the flies exposed to microgravity experienced neurological changes while those exposed to artificial gravity aged differently and faced less severe challenges acclimating once they returned.
These results suggest that spaceflight causes stress that leads to negative behavioral and neurological effects, as well as changes in gene expression in the fly brain. They also suggest that artificial gravity can mitigate these effects during spaceflight, though there are still long-term challenges when it comes to reacclimating to Earth. While these results cannot precisely predict the effects on human health, they offer an approximation and a good starting point for future research. As Dr. Siddhita Mhatre, a KBR Wyle senior scientist at Ames and an author of the paper, summarized:
“With the upcoming long-duration deep space missions, where astronauts will be exposed to varying levels of gravity, it is imperative that we understand the impacts of altered gravity on the neurological function. If we can use artificial gravity to delay space-related deficits, maybe we can extend the future mission timelines. And flies in space, alongside the astronauts, will help to further our efforts in keeping astronauts healthy.”
NASA is currently investigating centrifuges and artificial gravity for space stations and missions to deep space. Examples include the NASA concept study titled “Non-Atmospheric Universal Transport Intended for Lengthy United States Exploration” (NAUTILUS-X), a rotating torus-shaped module that would provide artificial gravity. NASA further proposed that a demonstration module (the ISS Centrifuge Demo) could become a Sleep Module for the ISS crew. This module would measure 9.1 m (30 feet) in diameter, have an interior diameter of 0.76 m (2.5 feet), and provide between 0.08 to 0.51 g of partial gravity.
It was also intended to provide a proof-of-concept for a larger torus that could be integrated into a possible spacecraft known as the Multi-Mission Space Exploration Vehicle (MMSEV). This concept and similar research studies highlight the importance of astronaut health and safety measures for long-duration spaceflights. As NASA and other space agencies send astronauts to the Moon (to stay this time) and pursue crewed missions to Mars and beyond, artificial gravity may become a regular feature of spacecraft, space stations, and even surface habitats.