It\u2019s been over half a century since humanity last set foot on the Moon. Those early \u201cbaby steps\u201d towards the stars remain some of our most defining achievements, yet the promise of a \u201cgiant leap\u201d to another planet still hangs unfulfilled. Interplanetary travel remains a dream, though visionaries like Elon Musk insist it\u2019s only a matter of time. \u201cEach launch,\u201d he says, \u201cis about learning what\u2019s needed to make life multiplanetary.\u201d<\/p>\n
But while SpaceX and others are tackling the technical side of rockets and propulsion, the far greater challenge may not lie in the machinery at all. Imagine reaching Mars only to collapse from exhaustion, or facing an invisible killer that warps your DNA. This isn\u2019t science fiction. It\u2019s the biological reality that awaits the first humans who dare to venture into deep space.<\/p>\n
In this first of a two-part exploration, we spoke to NASA scientists and physicians to understand the devastating effects of long-term space travel on the human body, and what we\u2019re doing to survive it.<\/p>\n
The human body vs. the void<\/p>\n
A trip to Mars isn\u2019t measured in miles but in months. Six to nine of them, traveling through a vacuum that\u2019s actively hostile to life. Unlike the relatively short missions to the Moon or the manageable environment of the International Space Station<\/a> (ISS), the journey to Mars represents an unmatched test of endurance.<\/p>\n Space doesn\u2019t just remove gravity. It removes the very conditions under which the human body evolved. Muscles weaken, bones dissolve, fluids redistribute, and the heart itself begins to shrink. Even the brain and immune system start to behave in unpredictable ways. In space, adaptation isn\u2019t optional. It\u2019s a desperate, ongoing battle for survival.<\/p>\n Microgravity: The enemy within<\/p>\n As soon as astronauts enter microgravity, every organ system begins to change. On Earth, gravity provides constant feedback that keeps the body balanced, muscles active, and bones strong. Take it away, and everything begins to unravel.<\/p>\n The first thing astronauts feel is disorientation, which NASA calls \u201cspace adaptation syndrome.\u201d Without gravity, the brain\u2019s balance system is thrown into chaos. Vision says one thing, while muscle and joint sensors say another. The result? Nausea, dizziness, headaches, and fatigue are feelings our expert describes as \u201cbeing a grumpy drunk.\u201d<\/p>\n The brain eventually adjusts, but the body continues to degrade. In zero gravity, bones lose density at an alarming rate, roughly 1% per month, compared to about 1% per year for an elderly person with osteoporosis on Earth. Muscles, especially in the legs and spine, begin to atrophy since they no longer need support or movement.<\/p>\n Even the spine itself stretches, causing astronauts to \u201cgrow\u201d a few centimeters taller in orbit, but at the cost of back pain. By the time astronauts return to Earth, their muscles are weaker, their bones more fragile, and their balance systems need retraining.<\/p>\n The body fluid revolution<\/p>\n On Earth, gravity pulls fluids toward the lower half of the body. In space, that distribution evens out. Blood and other fluids shift toward the head, creating the space travelers\u2019 signature \u201cpuffy face\u201d and \u201cchicken legs\u201d look.<\/p>\n This shift increases pressure in the skull and behind the eyes, sometimes leading to permanent vision problems. It also triggers a chain reaction in the cardiovascular system. The body senses too much fluid near the heart and brain and responds by eliminating what it perceives as excess. Astronauts<\/a> start to urinate more, losing about 10\u201315% of their blood plasma within days.<\/p>\n The heart, now working under less strain, begins to shrink. Red blood cells are destroyed to maintain balance, and blood pressure regulation becomes more erratic. The combined effects make returning to gravity or standing upright a painful, dizzying experience.<\/p>\n DNA, immunity, and the cellular cost of space<\/p>\n Space doesn\u2019t just challenge muscles and bones<\/a>. It reaches into the body\u2019s most fundamental processes. Studies comparing astronaut Scott Kelly, who spent a year aboard the ISS, to his twin brother Mark on Earth revealed startling differences. Scott\u2019s genes showed changes in expression related to DNA repair and immune response. His telomeres, protective caps on chromosomes, lengthened in space, only to shorten rapidly upon return.<\/p>\n Deprived of Earth\u2019s microbial environment and under constant radiation exposure, the immune system becomes unpredictable. Astronauts experience changes in white blood cell behavior, inflammation, and even allergic responses. Prolonged exposure could increase risks of cancer or autoimmune disorders, dangers that will grow exponentially on longer journeys.<\/p>\n Fighting back: Survival through exercise and engineering<\/p>\n NASA has learned one essential truth. Exercise isn\u2019t optional; it\u2019s medicine. Astronauts aboard the ISS dedicate more than two hours daily to workouts designed to mimic gravity\u2019s effects. They run on treadmills while strapped down by bungee cords, lift vacuum-based weights for resistance, and cycle for cardiovascular health. Despite this grueling regimen, astronauts still return home weaker than when they left. The problem is time. For more than 21 hours each day, their bodies are still weightless, continuing to waste away.<\/p>\n Researchers are now exploring advanced countermeasures: nutritional plans rich in protein and essential minerals, electrical muscle stimulation, and even pharmaceuticals that could slow down muscle and bone loss.<\/p>\n