What exactly happens to the body in space and what are the risks? Are the risks the same for astronauts who spend six months on the space station versus those who may be away on a Mars mission for years? The simple answer is “no.” NASA is researching risks for Mars missions which are grouped into five human spaceflight hazards related to the stressors they place on the body. These can be summarized with the acronym “RIDGE,” short for Space Radiation, Isolation and Confinement, Distance from Earth, Gravity fields, and Hostile/Closed Environments.
Understanding the effects of spaceflight on humans is essential as astronauts move from the International Space Station in low-Earth orbit to deep space destinations on and around the Moon, and beyond. With the Artemis program, NASA will land the first woman and next man on the Moon using innovative technologies to explore more of the lunar surface than ever before, gathering new data while keeping astronauts healthy and safe.
The space station orbits 240 miles above Earth. The Moon is 1,000 times farther from Earth than the space station. In contrast, Mars is on average 140 million miles from Earth. With a communication delay of up to 20 minutes one-way while on Mars, astronauts must be able to solve problems and identify solutions as a team without help from NASA’s mission control. The types of food and medicine to be packed for a multi-year trip without access to a grocery store or pharmacy are also important to consider. Unlike space station crews, which regularly receive supplies from cargo flights from Earth, astronauts going to Mars will have to bring all of the food, equipment, and medical supplies they need.
One of the main health concerns with space travel is radiation exposure. Deep-space missions, going beyond the inner planets, or even just one long mission to Mars and back, will be pushing the limits of what we know. It’s also approaching the estimated lifetime limits of radiation for human exposure.
In space, astronauts are exposed to varied and increased levels of radiation that are different from those on Earth. Three major sources contribute to the space radiation environment: particles trapped in Earth’s magnetic field, solar energetic particles from the Sun, and galactic cosmic rays. A big challenge in reducing the risks of radiation exposure is that some space radiation particles (especially galactic cosmic rays) are difficult to shield against. Exposure to increased radiation can be associated with both short- and long-term health consequences, depending on how much total radiation astronauts experience and the time frame in which they experience that exposure. Increased risk of cancer and degenerative diseases, such as heart disease and cataracts, have been observed in human populations exposed to radiation on Earth.
Damage to an organism’s DNA can occur during normal biological processes or as a result of environmental causes, such as UV light. In humans and other animals, damaged DNA can lead to cancer. Fortunately, cells have several different natural strategies by which damaged DNA can be repaired. On Earth, the body can repair double-strand breaks by adding and deleting DNA bases, or re-joining the two pieces without altering them.
Isolation and Confinement
Expedition crews selected for a stay onboard the space station are carefully chosen, trained, and supported to ensure they will be able to work effectively as a team for the duration of their six to 12-month missions. Crews for a Moon or Mars mission will undergo even more careful assessment, selection, and preparation since they will travel farther and potentially for longer than previous humans in an isolated and confined environment, with only a few other people. Additionally, crews will likely be international and multi-cultural, making cross-cultural sensitivity and team dynamics paramount to mission success. Ensuring astronauts get quality sleep is also important; otherwise, their internal biological clocks, or circadian rhythm, might be altered by factors like different dark and light cycles, a small and noisy environment, the stress of prolonged isolation and confinement, and a 37-minute extended day on Mars. It is important to prepare for the fatigue astronauts may experience during spaceflight, given that there will be times with heavy workloads and shifting schedules.
To prevent crew boredom, NASA considers the kinds of activities in which the astronauts will participate during a multi-year round trip to Mars. Communication and understanding among crew members are vital to the success of the mission, and changes in morale and motivation are possible as the mission unfolds. This may relate to reduced stimulation, the longing for loved ones, or feeling unable to assist with family emergencies back on Earth, regardless of how long the mission lasts. Using spaceflight analogs on Earth, NASA’s research has revealed that both the duration and type of confined and isolated experience are important to consider. The more restricted the space, and the less contact with people outside the environment, the more likely humans are to develop behavioral or cognitive conditions or psychiatric disorders.
NASA scientists are using devices, such as actigraphy, that help assess and improve sleep and alertness by recording how much people move and how much ambient light is around them. New lighting, spurred by the development of Light-Emitting Diode (LED) technology, is used on the space station to help align astronaut’s circadian rhythms and to improve sleep, alertness, and performance.
Researchers are also looking into using virtual reality to simulate relaxing environments to help improve the mood of crews in isolation. Engaging in relevant, meaningful activities, including learning a language or learning new medical skills, could help ward off depression and boost morale. Crews may even tend to a space garden, which could have positive behavioral health benefits in addition to providing a fresh source of food and helping to purify the air. Researchers are using Earth-based analogs to investigate how much privacy and living space will be needed on longer missions where crew members will be restricted in a relatively small spacecraft together.
Astronauts will encounter three different gravity fields on a Mars mission. On the six-month trek between the planets, crews will be weightless. While living and working on Mars, crews will be in approximately one-third of Earth’s gravity. Finally upon returning home, crews will have to readapt to Earth’s gravity. Transitioning from one gravity field to another is trickier than it sounds. It affects spatial orientation, head-eye and hand-eye coordination, balance, and locomotion, with some crew members experiencing space motion sickness. Landing a spacecraft on Mars could be challenging as astronauts adjust to the gravity field of another celestial body. When shifting from weightlessness to gravity, astronauts may experience post-flight orthostatic intolerance where they are unable to maintain their blood pressure when standing up, which can lead to lightheadedness and fainting.
NASA has learned that without Earth’s gravity affecting the human body, weight-bearing bones lose on average 1% to 1.5% of mineral density per month during spaceflight. After returning to Earth, bone loss might not be completely corrected by rehabilitation; however, their risk for fracture is not higher. Without the proper diet and exercise routine, astronauts also lose muscle mass in microgravity faster than they would on Earth.
Moreover, the fluids in the body shift upward to the head in microgravity, which may put pressure on the eyes and cause vision problems. If preventive or countermeasures are not implemented, crews may experience an increased risk of developing kidney stones due to dehydration and increased excretion of calcium from their bones.
Vision issues in space
NASA reported in 2020 that astronaut Michael Barratt who flew a six-month mission aboard the International Space Station suffered from Space-Associated Neuro-Ocular Syndrome (SANS). The symptoms include swelling in the optic disc, which is where the optic nerve enters the retina, and flattening of the eye shape. Steve Laurie, a scientist with NASA’s Human Health and Performance Directorate said that signs of SANS appear in roughly 70 per cent of crew members.
The new study published in Dec 2021 JAMA Ophthalmology found that three days of lying flat in a simulated microgravity environment-induced enough pressure to slightly alter the shape of the eyeball but no such change was seen when the new suction technology was used.
“We don’t know how bad the effects might be on a longer flight, like a two-year Mars operation,” said one of the authors Benjamin Levine in a release. He is a cardiologist who is helping NASA address the health risks of brain pressure and abnormal blood flow in space.
Researchers from the University of Texas have designed a new vacuum-equipped sleeping bag that can pull down body fluids that naturally flowed into our heads while sleeping in a supine position. When in space, astronauts can suffer from problems in vision as these fluids push and reshape the back of the eyeball.
The sleeping bag has a solid frame, shaped like a space capsule, and fits over a person from the waist down. The study included ten volunteers including one of the authors Dr James Leidner. He is an internal medicine hospitalist in San Antonio.
The researchers add that several questions need to be answered before NASA brings this technology to the space station, including the optimal amount of time astronauts should spend in the sleeping bag each day.
NASA has learned that the ecosystem inside the spacecraft plays a big role in everyday astronaut life in space. Microbes can change characteristics in space, and micro-organisms that naturally live on the human body are transferred more easily from person to person in closed habitats, such as the space station.
Stress hormone levels are elevated and the immune system is altered, which could lead to increased susceptibility to allergies or other illnesses. Earth-based analogs do not perfectly simulate the spaceflight environment, making them insufficient for studying on the ground how human immune systems react in space.
However, NASA-funded Antarctic analog studies could provide insight into how certain spaceflight stressors may affect the human immune system. What is known is that spaceflight changes the immune system, although crews do not tend to get sick upon returning to Earth. Even though astronauts’ acquired immunity is intact, more research is needed into whether spaceflight induced altered immunity may lead to autoimmune issues, in which the immune system mistakenly attacks the healthy cells, organs, and tissues present in the body.
Beyond the effects of the environment on the immune system, every inch and detail of living and working quarters must be carefully thought-out and designed. No one wants their house to be too hot, too cold, cramped, crowded, loud, or not well lit, and no one would enjoy working and living in such a habitat in space either.
Space station astronauts already receive medical training before and during space missions that teach them how to respond to health problems as they arise. For example, astronauts learn how to use onboard space station equipment to produce an intravenous (IV) solution from purified water, which can be used for medical administration. Crew members also perform ultrasound scans on each other to monitor organ health. If one crew member becomes sick during the mission, crews are ready to perform laboratory testing to help make the right diagnosis and guide treatment.
NASA is working on developing a medical data architecture for spacecraft that enables the capabilities of clinical decision support tools, which could use artificial intelligence and machine learning to further help diagnose and treat various illnesses. Researchers are also looking into the role that virtual assistants could play to help crews identify and respond to spaceflight anomalies quickly for more distant missions.
NASA’s Human Research Program (HRP)
NASA’s Human Research Program (HRP) has been studying what happens to the human body in space. Researchers are using what they learn to design procedures, devices, and strategies to keep astronauts safe and healthy throughout their missions.
NASA engineers use the lessons learned to better design spacecraft and improve the fit and functions of spacesuits. The research also aids in the development and assessment of medical standards, physical fitness programs and standards, physiological and psychological adaptation training, sensorimotor training, and nutritional health protocols.
NASA is particularly interested in investigating how the body reacts to long-duration spaceflight as the agency plans for extended missions on the Moon and Mars. Scott Kelly and Christina Koch were the first American astronauts to spend nearly one year in space onboard the space station, twice the previous average. Scott, Christina, and six other astronauts have spent more than 200 days in space during a single spaceflight.
In addition to spending almost a year in space, Scott was involved in the unique Twins Study. Scott participated in several biomedical studies onboard the space station while his identical twin brother, retired astronaut Mark Kelly, stayed on Earth as a control subject, someone who provides a basis of comparison. The study provided valuable data about what happened to Scott, physiologically and psychologically, as compared to his brother Mark. Their contribution to science helped generate data that researchers will use for decades to come.
NASA is planning more dedicated extended-duration research on the space station. The studies are expected to shed light on how the body adapts to living in the spaceflight environment for various longer time periods, which will be pivotal for future deep space missions.
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