The Human Body and Mind After Space Travel

The surreal memories of the extended COVID-19 lockdown stay-at-home period are still fresh in many minds. However, this experience of confinement is even more familiar to NASA astronauts Suni Williams and Barry “Butch” Wilmore, who recently returned to Earth on March 18, 2025 aboard the SpaceX Crew Dragon Capsule. The astronauts were originally launched into space aboard the Boeing Starliner on June 5, 2024. They were expected to work on the International Space Station (ISS) for only eight days. However, their return was delayed for nine months due to helium leaks in the Starliner’s propulsion system. Unfortunately, such prolonged time in space has had both short-term and long-term effects on astronaut health and well-being. 

When Williams and Wilmore returned to Earth, they immediately felt nauseated because the ear’s vestibular system—which consists of sensory organs in the inner ear important for maintaining bodily balance—needed time to readjust. Your inner ear contains endolymph fluid and hair cell sensory receptors. When your body moves, this fluid shifts, causing the hair cells to move. This movement then sends nerve signals to your brain via the vestibular nerve. However, in space, microgravity causes the endolymph to flow upwards. Microgravity refers to the condition in which objects are experiencing free-fall—their net acceleration is equal to the gravitational acceleration. Thus, the disparity in endolymph movement between on Earth and in space causes a sense of disorientation analogous to learning how to walk for the first time. Upon returning to Earth, astronauts also tend to shrink in height due to microgravity in space. On the ISS, both the astronaut and the ISS experience free-fall (the same amount of acceleration), causing the astronaut to float. This floating results in the expansion of an astronaut’s spinal column. When the astronaut returns to Earth, the astronaut no longer experiences free-fall and floating, so their spinal disks compress. This compression can induce back pain since the newly returned astronaut is not accustomed to actively sustaining posture. 

Beyond immediate effects upon landing, extended space time also has long-term effects on the musculoskeletal, immune, cardiovascular, and visual nervous systems. The upward flow of bodily fluids to the head causes increased eye pressure and vision issues. Such issues include swelling of the optic nerve, folds in the retina, flattening of the back eye, and blurry vision. A similar upward flow of cerebrospinal fluid causes the brain to situate itself higher in the skull and causes the brain’s ventricles to expand—a condition similar to fetal ventriculomegaly, which results in irregular sleep patterns and abnormal eye movements. Moreover, microgravity causes the heart to take on a more spherical shape and the arteries to stiffen. Therefore, prolonged spaceflight increases the risk of atrial fibrillation, an irregular heartbeat. For each month in space, astronauts’ bones become one percent less dense. Even though astronauts counteract this by working out while in space, they still feel unaccustomed to simple things like sitting in a hard chair back on Earth. Additionally, in space, astronauts’ immunity to germs native to Earth is suppressed, making the astronauts vulnerable to infection upon return. Finally, astronauts develop “baby feet.” In space, their feet don’t have to support their bodies’ weight. As a result, the thick skin under their feet falls off, and their feet become more pressure-sensitive.

The psychological impacts of extended space travel also complement its physical impacts. Due to limited social interaction in confined spaces, astronauts tend to experience stress, sleep disturbances, and mood disorders. Wilmore and Williams reported constant longing for their families back on Earth. The anxiety over the success of re-entry into Earth, especially after being stranded in space for nine months, can induce sleep irregularities. Changes in mood are also induced by the absence of natural light on board. Shorter exposures to light stimulate anxiety and depression, while longer exposure to light has the opposite effect. This is attributed to how disruptions in the circadian rhythm (the “body clock”) lead to mood disorders. On Earth, the circadian rhythm is influenced by the change in natural lighting from the Sun over each 24-hour period. However, astronauts are not subject to the gradual change in sunlight in space, leading to mood abnormalities and a disruption in their circadian rhythm. 

In order to alleviate the effects of prolonged spaceflight on an astronaut’s physical and psychological health, Wilmore and Williams are currently undergoing a 45-day rehabilitation routine. Phase One focuses on ambulation, flexibility, and muscle strengthening while Phase Two involves proprioceptive exercise and cardiovascular training. Lastly, Phase Three—the longest phase of all—focuses on functional development. For example, to help their vestibular system readjust, the astronauts avoid turning their bodies due to their vulnerability to disorientation. Hence, the astronauts are taught to walk in a straight line and then walk in a curve. 

In light of the implications of space travel on astronaut health, space agencies are taking strides to minimize space’s harm on astronaut physical and mental health. NASA is developing new radiation detectors to monitor how much cosmic radiation the astronaut crews are exposed to, since radiation could lead to an increased risk of cancer. To maintain a normal circadian rhythm and mood regulation, the European Space Agency implemented a new lighting system on the ISS. The light spectrum from an automated LED panel periodically changes within each 24-hour cycle. The astronauts’ circadian rhythms are then monitored by non-invasive skin sensors that track body temperature fluctuations throughout the day. This monitoring determines the regularity of the circadian rhythms. For improving mental wellbeing, astronauts on the ISS are given images taken on Earth, ranging from urban growth to changes in icebergs. Crew members also write diary entries reporting on work, outside communication, group interaction, leisure time, and more. These entries provide vast insight into the impact of space travel on human performance, as well as recommendations for further astronauts’ preparation for extended space time. 

Wilmore and Williams’s delayed returns indicate greater attention for astronauts’ physical and mental well-being. As space agencies continue to find solutions to health problems linked to space travel, astronauts can hope to feel at home in space regardless of the duration of their travels.