What are Spaceflight Human Factors?

The Human Element

Spaceflight is an endeavor of extremes. It pushes machines to their absolute limits of performance, durability, and precision. Yet, rocketry, orbital mechanics, and advanced materials are only part of the equation. At the very center of every mission, from the first tentative suborbital hops to ambitious plans for interplanetary journeys, is the human being. This “human element” is simultaneously the most capable and most vulnerable component of any space mission. Managing this component is the domain of spaceflight human factors.

This field is a complex, interdisciplinary science that sits at the intersection of psychology, physiology, medicine, engineering, and industrial design. It’s not just about astronaut comfort or morale. It’s a fundamental engineering discipline that seeks to understand the human body and mind, quantify its limitations, and then design the hardware, software, habitats, and procedures to make that human safe, healthy, and productive in the most hostile environment ever encountered. It asks not “Can a human survive this?” but rather, “What systems do we need to build so a human can thrive, work efficiently, and return home safely?”

The environment of space is significantly unforgiving. On Earth, human life is protected by a thick atmosphere, a strong magnetic field, and the constant pull of gravity. In space, astronauts are exposed to a vacuum, extreme temperature swings, a complex radiation field, and the pervasive, disorienting effects of weightlessness. An error that might be a simple inconvenience on Earth – like misreading a display or fumbling with a tool – can lead to catastrophic failure in orbit.

Historically, the focus of human factors has evolved. The Mercury program was a test of basic survival. Engineers at NASA weren’t entirely sure a human could even swallow food or maintain consciousness in microgravity. The astronauts of that era were often seen as test subjects, passengers in fully automated capsules. It was only after astronauts like Alan Shepard and John Glenn insisted on having a window and manual controls that the human-in-the-loop concept began to take hold. They proved that a human pilot was not a liability but an asset, capable of diagnosing problems and salvaging missions that computers alone would have lost.

Today, on the International Space Station (ISS), astronauts are no longer just pilots. They are scientists, mechanics, doctors, and engineers, performing complex experiments and maintaining a vast, orbiting laboratory. As space agencies like NASA and its international partners, along with commercial companies like SpaceX and Boeing, set their sights on the Moon and Mars, the challenges for human factors are expanding dramatically. A trip to the ISS means being a few hours from home. A trip to Mars will involve years of isolation, with crews operating almost entirely on their own, separated from Earth by a 20-minute communication delay.

Understanding spaceflight human factors means examining three distinct but interconnected pillars: the physiological impact of space on the body, the psychological impact of isolation on the mind, and the complex engineering of the human-machine interface.

The Physiological Challenge: The Body in Space

The human body is a product of 3.8 billion years of evolution in a one-gravity (1g) environment. It is exquisitely adapted to Earth. When placed in the microgravity, or “weightlessness,” of space, it immediately begins to change. These changes are dramatic, widespread, and affect nearly every system. A significant portion of human factors research is dedicated to understanding these effects and, more importantly, developing countermeasures to mitigate them.

The Weightless Environment: Microgravity Effects

From the moment an engine cuts off and a spacecraft enters orbit, the body is in a state of freefall. The inner ear’s vestibular system, which tells us “which way is up,” is suddenly adrift without gravity’s constant pull. The cardiovascular system no longer has to fight gravity to push blood to the brain. The bones and muscles no longer need to support the body’s weight. The body, sensing this new environment, begins to adapt, and these adaptations are almost all negative for a return to Earth.

Space Adaptation Syndrome (SAS)

Commonly known as “space sickness,” SAS affects 60-80% of all astronauts, typically within the first 72 hours of a mission. It’s the body’s direct response to a sensory conflict. The eyes see the inside of the capsule and can define a “floor” and “ceiling,” but the vestibular system in the inner ear, which senses motion and orientation, reports that it’s tumbling in freefall. This mismatch between the eyes and the inner ear sends confusing signals to the brain, resulting in the classic symptoms of motion sickness: disorientation, vertigo, headaches, loss of appetite, and in many cases, severe nausea and vomiting.

This isn’t just a matter of comfort. On a tightly scheduled mission, having half the crew incapacitated for the first three days is a major operational problem. An astronaut suffering a sudden bout of vomiting inside a spacesuit during a spacewalk could face a life-threatening emergency. Over time, the brain learns to ignore the “faulty” signals from the inner ear and relies more heavily on visual cues. This adaptation makes the return to Earth just as difficult, as the brain must then re-learn to trust the vestibular system. Countermeasures include medications (like scopolamine patches) and techniques like minimizing head movements in the first few days of flight.

Fluid Shift

On Earth, gravity pulls blood and other bodily fluids down toward the legs and feet. The cardiovascular system is designed to constantly push these fluids “uphill” to the upper body and brain. In microgravity, this “uphill” battle disappears. The result is a massive redistribution of fluids, with up to two liters moving from the lower body to the chest and head.

This is known as the cephalad fluid shift, and it has immediate, visible consequences. Astronauts develop a “puffy face” and “bird legs,” as their face swells with fluid and their legs shrink. This shift causes a cascade of other problems. The swelling in the head leads to persistent sinus and nasal congestion, dull headaches, and a diminished senseof taste and smell (which also impacts food psychology). The body’s sensors, detecting this “excess” fluid in the torso, interpret it as over-hydration. This tricks the kidneys into increasing urine output, leading to a rapid loss of fluid and a decrease in overall blood volume. This reduced blood volume is fine in space, but it’s a primary cause of fainting and dizziness when astronauts return to Earth’s gravity.

Cardiovascular Deconditioning

The heart is a muscle. Without gravity, it simply doesn’t have to work as hard. The left ventricle, which does the heavy lifting of pumping blood to the entire body, begins to slightly atrophy, much like an athlete’s muscles after a long period of inactivity. Combined with the lower blood volume from the fluid shift, the entire cardiovascular system becomes “deconditioned.”

This is not a problem for life in orbit. The problem arises upon return. When an astronaut lands and stands up, gravity immediately pulls that reduced blood volume back down to the legs. The deconditioned heart, not used to the strain, can fail to pump enough blood to the brain. This condition is called orthostatic intolerance, and it results in lightheadedness, a racing pulse, and a high risk of fainting. This is why returning astronauts are often carried out of their capsules. It’s not just for show; they may be physically unable to stand or walk without assistance.

Bone Density Loss

This is one of the most serious long-term effects of spaceflight. On Earth, our bones are in a constant state of remodeling, with specialized cells called osteoblasts building new bone and osteoclasts breaking down old bone. This process is regulated by mechanical stress – the simple acts of walking, running, and standing.

In microgravity, this mechanical loading vanishes. The body interprets this as the bones no longer being needed for support. The bone-building process slows down, while the bone-breakdown process continues or even accelerates. The result is a rapid, osteoporosis-like loss of bone density, particularly in load-bearing bones like the femurs, hips, and lower spine. Astronauts can lose 1% to 2% of their bone mass per month in space. On Earth, an elderly person with osteoporosis might lose that much in an entire year.

This bone loss makes the skeleton more fragile, increasing the risk of fractures during reentry, landing, or even just stumbling after returning to Earth. The lost bone mineral, primarily calcium, doesn’t just disappear. It’s released into the bloodstream, which taxes the kidneys and significantly increases the risk of developing painful kidney stones in-flight, a medical emergency that is very difficult to treat in space.

Muscle Atrophy

Similar to bones, muscles operate on a “use it or lose it” principle. In microgravity, the large postural muscles – the calves, quadriceps, back, and neck muscles used to stand upright and hold the head up – are almost completely unloaded. They begin to atrophy (waste away) quickly. Astronauts can lose up to 20% of their muscle mass on a six-month mission.

This isn’t just a loss of bulk; it’s a loss of strength and endurance. The muscle fibers themselves change, with slow-twitch endurance fibers (used for posture) being replaced by fast-twitch fibers (used for quick bursts of movement). This muscle wasting impairs an astronaut’s ability to perform strenuous tasks, especially during spacewalks (Extravehicular Activities, or EVAs). It’s also a primary reason they struggle to walk upon landing. Without a rigorous countermeasure program, an astronaut landing on Mars after a six-month transit would be too weak to walk, let alone perform emergency procedures or construction tasks in a heavy spacesuit.

Countermeasures: Fighting the Void

Because these physiological changes are so severe, a massive part of the human factors effort on the ISS is dedicated to countermeasures. The current strategy is a multi-pronged approach involving exercise, nutrition, and medical monitoring.

Exercise Hardware

Astronauts on the ISS are required to exercise for about 2.5 hours every single day. This isn’t for general fitness; it’s a medical necessity to combat bone and muscle loss. Designing exercise equipment that works in weightlessness is a major human factors engineering challenge.

• Resistance Training: The Advanced Resistive Exercise Device (ARED) is the primary tool for fighting muscle and bone loss. It’s a complex machine that uses vacuum cylinders to simulate free weights, allowing astronauts to perform squats, deadlifts, and bench presses with up to 600 pounds of force. The mechanical loading from ARED is currently the best way to signal to the bones that they are still needed.
• Cardiovascular Training: This is handled by two devices. The Treadmill 2 (COLBERT) requires astronauts to strap themselves down with a harness of springs and bungees to simulate their body weight and keep them from floating away. The Cycle Ergometer with Vibration Isolation System (CEVIS) is a stationary bike. Both are essential for maintaining heart health and aerobic capacity. A key design feature of this equipment is vibration isolation. Without it, the force of an astronaut running on a treadmill would shake the entire ISS and ruin sensitive microgravity experiments.

Nutritional Support

Nutrition is another key countermeasure. Astronauts must consume enough calories to fuel their intense workouts. They are also placed on high-vitamin D diets. On Earth, we get vitamin D from sunlight, but the ISS environment is shielded, and astronauts don’t get direct sun exposure. Vitamin D is essential for calcium regulation and bone health. Diets are also carefully managed to reduce sodium, which can exacerbate bone loss.

This table summarizes the main physiological challenges and their corresponding countermeasures.

The Radiation Environment

If microgravity is the main hazard of Low Earth Orbit (LEO), radiation is the dragon waiting for us in deep space. The ISS is still largely within the protection of Earth’s magnetic field, the Van Allen belts, which deflect the worst of space radiation. But on a mission to the Moon or Mars, astronauts will be fully exposed.

There are three main sources of space radiation:

1. Trapped Radiation: The Van Allen belts themselves. Missions must transit them quickly to minimize exposure.
2. Solar Particle Events (SPEs): These are sudden, unpredictable eruptions from the Sun, like solar flares or coronal mass ejections. They release massive quantities of high-energy protons. A large, unshielded SPE could deliver a lethal dose of radiation to an astronaut in a matter of hours. Missions must be designed with a “storm shelter,” a heavily shielded area of the spacecraft (often using water tanks and food supplies) where the crew can hide.
3. Galactic Cosmic Rays (GCRs): This is the most serious long-term radiation problem. GCRs are the “background” radiation of the universe, originating from distant supernovae. They are atomic nuclei (from hydrogen up to iron) that have been accelerated to nearly the speed of light. They are incredibly penetrating.

Unlike the protons from SPEs, GCRs are very difficult to shield against. When a high-energy GCR (like an iron nucleus) strikes the aluminum hull of a spacecraft, it doesn’t stop. It shatters, creating a “secondary radiation” shower of smaller, still-high-energy particles inside the spacecraft. In this case, standard shielding can sometimes make the internal radiation environment worse. The best shields are hydrogen-rich materials, like water, polyethylene (a type of plastic), or potentially Martian regolith (soil) piled on top of a habitat.

The health risks are significant. The primary concern is an increased lifetime risk of cancer. But GCRs can also cause damage to the central nervous system, leading to cognitive decline, memory problems, and a “space fog” that could impair an astronaut’s ability to perform complex tasks. Cataracts are also a common long-term side effect. Human factors specialists at facilities like the NASA Space Radiation Laboratory at Brookhaven National Laboratory are actively working to understand these effects and set career exposure limits for astronauts.

Spaceflight Associated Neuro-ocular Syndrome (SANS)

A more recent and disturbing discovery is Spaceflight Associated Neuro-ocular Syndrome (SANS). For years, astronauts returning from long-duration missions on the ISS reported changes to their vision. Many who left with perfect 20/20 vision returned needing glasses.

When NASA investigated, they found physical, measurable changes to the astronauts’ eyes. The cephalad fluid shift appears to increase the pressure inside the skull (intracranial pressure). This pressure pushes on the back of the eyeball, causing it to flatten slightly. This flattening changes the eye’s focal length, leading to farsightedness (hyperopia). They also discovered swelling of the optic nerve (optic disc edema) and other structural changes.

SANS is a major concern because, in some astronauts, these changes are not fully reversible upon return to Earth. We simply don’t know what will happen to an astronaut’s vision after a three-year mission to Mars. This syndrome highlights a key part of human factors: the body is an integrated system, and a change in one area (the cardiovascular fluid shift) can have unexpected, cascading consequences in another (vision).

The Psychological Challenge: The Mind in Isolation

If the body can be protected with exercise and shielding, the mind presents a more subtle and complex challenge. A mission to Mars won’t be a thrilling six-month sprint; it will be a three-year journey of monotony, confinement, and extreme isolation. The “Right Stuff” – the stoic, steely-nerved test pilot – is only part of what’s needed for long-duration exploration. Psychological human factors focus on crew selection, behavioral health, team dynamics, and providing support for the mind.

Isolation and Confinement

Humans are social animals, evolved to live in small groups in a wide-open, dynamic, sensory-rich environment. A deep-space mission is the exact opposite of this.

The “Earth-Out-of-View” Phenomenon

On the ISS, astronauts can look out the Cupola and see the Earth rotating below, a constant, beautiful reminder of home. They can have real-time video conferences with their families. On a trip to Mars, the Earth will shrink to a “Pale Blue Dot,” and then, just another bright star in the blackness. This significant disconnection is a powerful psychological stressor. Many Apollo astronauts reported experiencing the “Overview Effect,” a feeling of awe and global unity, but the long-term version of this for a Mars crew is unknown.

Sensory Deprivation and Monotony

A spacecraft is a sterile, artificial environment. The sounds are the constant, unchanging hum of fans, pumps, and computers. The smells are of machine oil, ozone, and recycled air. The view out the window (except for the occasional planet) is mostly blackness. There is no weather, no wind, no rain, no new faces, and no new food. This monotony can lead to boredom, depression, and cognitive slowing.

Analog Environments

We can’t just send a crew to Mars and “see what happens.” Human factors research relies heavily on analog environments on Earth to simulate the isolation and confinement of space.

• Antarctic Stations: Research stations in Antarctica, like the Amundsen-Scott South Pole Station or the French-Italian Concordia Station, are high-fidelity analogs. During the “winter-over,” a small crew is completely isolated for six to eight months in total darkness, extreme cold, and a high-altitude (low-oxygen) environment. They cannot be evacuated for any reason.
• HI-SEAS (Hawaii Space Exploration Analog and Simulation): This NASA-funded program isolates crews in a small dome on the slopes of the Mauna Loa volcano for missions lasting up to a year.
• MARS-500: An experiment by Roscosmos and the European Space Agency (ESA) sealed a six-man international crew into a simulated Mars spacecraft in Moscow for 520 days – the full duration of a round-trip mission.

These studies have consistently shown that morale and crew cohesion are not static. They often dip significantly around the “third quarter” of the mission, just after the halfway point, when the novelty is gone but the end is still far away.

Cognitive and Behavioral Effects

The stress of isolation, combined with other factors, can directly impair an astronaut’s ability to think and perform.

Sleep Disruption

Sleep is one of the biggest human factors problems on the ISS. There is no “night” or “day” in orbit; the station circles the globe every 90 minutes, experiencing 16 sunrises and 16 sunsets. The circadian rhythm is completely thrown off. The environment is also noisy, the C02 levels are often high (which can cause headaches), and sleeping in a “bag” strapped to the wall is not natural. As a result, astronaut sleep is often short, fragmented, and of poor quality. The use of sleep-aid medication is very common. Chronic sleep deprivation leads to fatigue, irritability, and a much higher risk of making operational errors.

Stress and Asthenia

“Asthenia,” or the “space-lag” syndrome, is a well-documented condition characterized by a general lack of energy, cognitive slowing, irritability, and emotional fatigue. It’s a “burnt-out” feeling that can stem from the combination of sleep loss, a heavy workload, and the monotonous environment.

The Communication Delay

This is the single biggest operational change for a Mars mission. Radio waves travel at the speed of light, which means a message from Mars to Earth can take anywhere from 4 to 22 minutes, one way. A “conversation” would involve a 40-minute round-trip delay.

This completely changes the relationship between the crew and Mission Control. On the ISS, if an alarm goes off, an astronaut can call Houston, and an army of engineers will immediately swarm the problem. On a Mars mission, the crew is on their own. They can’t ask, “What does this light mean?” They must have the training, procedures, and autonomy to diagnose and fix the problem themselves. This “Earth independence” is a huge psychological shift, placing immense pressure on the crew. It also means no real-time calls with family, only “space voicemails.”

Interpersonal and Team Dynamics

When you can’t leave, small interpersonal irritations can escalate into major conflicts. Human factors isn’t just about one person; it’s about the “crew system.”

Crew Selection

NASA and other agencies have moved from selecting “aces” to selecting “team players.” The astronaut selection process now screens heavily for “expeditionary behavior” – positive psychological traits like resilience, emotional stability, empathy, patience, and good followership. A crew of “commanders” will likely fail. A successful crew needs a mix of personalities who can support each other, manage conflict, and maintain group morale.

Cultural Differences

The ISS is a model of international cooperation, but it’s also a human factors experiment. NASA astronauts, Roscosmos cosmonauts, ESA astronauts, and others must live and work together. They come from different cultures with different communication styles, different approaches to humor, different concepts of personal space, and even different food preferences. A great deal of pre-flight training is dedicated to cross-cultural communication and team-building to bridge these gaps.

Conflict and Leadership

Conflict is inevitable on a long mission. The challenge is managing it constructively. A famous (though often exaggerated) incident occurred on Skylab 4 in 1973. The crew, feeling overworked and stressed by a relentless schedule from the ground, eventually staged a sort of work slowdown, taking an unscheduled day off and demanding more control over their own time. This event was a lesson for NASA, highlighting that a crew’s psychological well-being and sense of autonomy are essential for mission success. Modern mission planning now builds in protected private time and flexibility.

Psychological Support Systems

You can’t just select a good crew and hope for the best. You need to actively support their mental health for the entire mission.

• Pre-flight Training: Crews train together for years, not just on technical skills but on “soft” skills. They go on wilderness expeditions (like NOLS) to learn how to function as a team under duress.
• Connection to Home: This is a vital morale booster. Private video conferences, email, and “care packages” with favorite foods or items from home are all scheduled events.
• Meaningful Work: The best antidote to boredom is a schedule filled with meaningful, challenging work. Astronauts are high-achievers; they need to feel productive.
• Recreation: Downtime is just as important. The ISS is stocked with movies, music libraries, books, and musical instruments (like Chris Hadfield’s famous guitar). The Cupola window is the most popular “recreation” spot, as astronauts spend hours simply watching the world go by.
• Food Psychology: Space food has improved immensely since the days of squeeze-tubes. The NASA food lab works to create a wide variety of meals that are not just nutritious but also appetizing. Food is a major psychological comfort. A “bonus” pack of a favorite snack can be a huge morale lift.
• Professional Support: Astronauts have regular private conferences with flight surgeons and psychologists on the ground to talk through any stress, fatigue, or conflicts they may be experiencing.

The Human-Machine Interface: Designing for Space

The third pillar of human factors is the “human-machine interface” (HMI) or “human-computer interaction” (HCI). This is the tangible world the astronaut interacts with: the design of the cockpit, the software, the tools, the habitat, and the spacesuit. Every object, from a waste-bin lid to a rocket’s control panel, must be designed for its unique context of use in space.

Habitability: Living in a “Tin Can”

“Habitability” refers to the quality of the living environment. A poorly designed habitat can be a constant source of stress, inefficiency, and error.

Architecture and Volume

Early capsules like Mercury and Apollo command and service module were incredibly cramped. Astronauts were essentially strapped into a pilot’s seat for the entire mission. The ISS, by contrast, is a mansion, with the internal volume of a Boeing 747. This volume is a human factors requirement. In microgravity, astronauts can use the entire volume – floors, walls, and ceilings are all work surfaces. But this can also be disorienting. A key design principle is creating a consistent “local vertical.” This means orienting lights, labels, and equipment so there is a clear “up” and “down” within a module, even if “down” is just another wall.

Personal Space

Even in a large volume, privacy is essential. On the ISS, each crew member has a private “sleep station,” a tiny, phone-booth-sized cabin called the Crew Quarters. It contains a sleeping bag, a laptop, and a few personal effects. This small, private space is a psychological necessity – a “room of one’s own” where an astronaut can be off-duty, write emails, or just be alone.

Lighting, Noise, and Waste

• Lighting: The ISS is being refit with LED lighting that can change its color temperature. Bright, blue-tinted light is used during the “day” to promote alertness, while warmer, reddish-tinted light is used in the “evening” to help stimulate the body’s circadian rhythm and prepare for sleep.
• Noise: The ISS is loud. The continuous hum of the life support systems – fans circulating air, pumps moving coolant, CO2 scrubbers – is about as loud as a vacuum cleaner. This noise is a major source of stress and a primary cause of sleep disturbance. Astronauts often have to wear earplugs. Designing quieter fans and better acoustic dampening is a high priority.
• Waste Management: The space toilet is a classic human factors problem. How do you collect waste when it won’t “fall” down? The solution uses airflow. The toilet is essentially a vacuum cleaner that sucks waste into a container. The design must be easy to use for both men and women, easy to clean, and extremely reliable. A malfunctioning toilet on a long-duration mission is a sanitary and morale disaster.

Cockpits, Controls, and Displays

The HMI of the spacecraft itself has evolved dramatically, reflecting our understanding of human factors.

The Evolution of the Cockpit

The Space Shuttle cockpit was a product of 1970s design. It was a forest of over 2,000 physical switches, dials, and “steam gauges.” A pilot had to memorize the location of hundreds of controls. While this provided excellent tactile feedback – you could feel a switch click even with gloves on – it was also a source of information overload.

Contrast this with the cockpit of the SpaceX Crew Dragon. It’s a “glass cockpit,” dominated by three large touchscreens. This design is flexible, cleaner, and can show the crew only the information they need for a specific phase of flight (e.g., launch, rendezvous, or reentry). This reduces cognitive clutter.

The Touchscreen Debate

The Crew Dragon design sparked a human factors debate. Touchscreens lack the tactile feedback of a physical switch. How do you accurately press a button on a smooth glass screen while wearing gloves, or more importantly, while shaking violently during launch or a rough reentry? How do you prevent the “fat finger” problem of hitting the wrong button? SpaceX’s solution was a combination of user interface design (making buttons large) and retaining a few physical buttons for emergency functions like “abort.” Boeing’s Starliner capsule took a hybrid approach, using a glass cockpit but retaining more physical switches and knobs based on astronaut feedback.

Information Design and Error Prevention

A good HMI doesn’t just present data; it helps the user make the right decision. This means designing alarms that are clear and prioritized. If 100 alarms go off at once (as happened during the Three Mile Island nuclear accident, a classic human factors failure), the operator can’t know what’s important. Modern systems prevent “alarm fatigue.”

Good design also prevents human error. A classic example is a “forcing function.” A connector that is designed to be physically impossible to plug in backward is a forcing function. Color-coding (e.g., red for emergency, yellow for caution) is another. Procedures are often written as checklists, not paragraphs, because the checklist format is a cognitive tool that ensures no step is missed – a lesson learned from aviation.

Anthropometry

Anthropometry is the science of human body measurement. It’s a core human factors discipline. Spacecraft must be designed to accommodate the full range of human body sizes. A switch must be reachable by the shortest astronaut, and the tallest astronaut must have enough headroom to avoid injury.

This is more complex than it sounds. In microgravity, the spine lengthens, and astronauts can “grow” up to two inches. A seat or spacesuit that fit perfectly on Earth may become too small in orbit. The “fluid shift” makes hands puffy and less dexterous, which must be accounted for in button and tool design. The failure to have enough medium-sized spacesuit torsos ready on the ISS in 2019, which led to the postponement of the first all-female spacewalk, was not an engineering failure but a human factors logistics failure.

The Spacesuit: A Personal Spacecraft

The spacesuit, or Extravehicular Mobility Unit (EMU), is the ultimate human-machine interface. It is a self-contained, one-person spacecraft that provides life support, radiation shielding, temperature control, and communications. It is also a notorious human factors challenge.

Mobility and Fatigue

The EMU is pressurized. This means the suit is essentially an inflated, human-shaped balloon. Every single movement – bending an elbow, closing a hand – requires the astronaut to fight against that internal pressure. This is exhausting. Spacewalks are often 6-8 hours long, and astronauts report that the most fatiguing part is simply working against the suit. Shoulder injuries are one of the most common long-term complaints from the astronaut corps, caused by the strain of maneuvering the suit’s rigid upper torso.

The Glove Problem

The gloves are, by far, the most difficult part of spacesuit design. They must be flexible enough to allow an astronaut to grip tools and turn bolts, but also durable enough to withstand micrometeoroid impacts and sharp edges. They must also be pressurized. The combination of stiffness and bulk makes fine motor tasks incredibly difficult. Astronauts often suffer from hand fatigue, cramps, and even fingernail injuries (onycholysis), where the constant pressure on their fingertips can cause their nails to delaminate and fall off.

Planetary Suits

The current EMU is designed for 0g. It’s a heavy, bulky suit that astronauts “wear” by floating inside it. A suit for the Moon or Mars presents new challenges. It must be lighter, more flexible, and allow for walking, kneeling, and bending over to pick up rocks. It must also contend with abrasive, electrostatically-charged dust (like the Apollo lunar dust) that can clog seals and filters. NASA’s new Exploration Extravehicular Mobility Unit (xEMU) for the Artemis program is being designed with these human factors in mind, featuring advanced bearings and a rear-entry “hatch” to make it easier to get in and out of.

The Future: Human Factors for Mars and Beyond

As humanity prepares to leave LEO and become a multi-planet species, the human factors challenges are becoming the primary hurdles to overcome.

Autonomy and the 20-Minute Light Lag

As mentioned, the communication delay to Mars forces crew autonomy. This will fundamentally change HMI. Mission Control will no longer be a real-time director but a “consultant” who can only offer advice 40 minutes after a question is asked.

• AI “Virtual Crewmates”: The crew will need intelligent support systems. This could be an AI, similar to the computer on Star Trek, that can understand plain-language queries. An astronaut could ask, “What is the procedure for a C02 scrubber failure?” or “What are the possible diagnoses for this medical symptom?” This AI would provide procedure support, system diagnostics, and scheduling management.
• The “Human-in-the-Loop”: The human factors of automation are complex. If a crew becomes too reliant on an AI, their own skills may degrade. They must be kept “in the loop,” actively monitoring and understanding the systems, not just passively watching. The HMI must be designed to facilitate this partnership, not just delegate tasks to the machine.

Medical Autonomy

On the ISS, if an astronaut has a severe medical emergency (like appendicitis or a heart attack), they can be stabilized and returned to Earth in a Soyuz or Crew Dragon capsule within 24 hours. This is called “medevac.”

From Mars, there is no medevac. The crew must be their own hospital. At least one crew member will likely be a medical doctor, but they will need tools far beyond a simple first-aid kit. Human factors research is looking into:

• Advanced Diagnostics: Portable ultrasound devices, compact blood analyzers, and digital stethoscopes that can send data to an AI diagnostic system.
• Telesurgery: This is impossible due to the light lag. You can’t have a surgeon in Houston remotely controlling a robot on Mars.
• Robotic-Assisted Surgery: The more likely scenario is a robotic surgical system that is controlled by the crew’s medical officer. The robot would provide stability and precision that is difficult for a human in a stressful environment. The human factors challenge is designing a system that a non-specialist (e.g., a crew doctor who is an internist, not a surgeon) could use to perform an emergency appendectomy.

Partial Gravity Environments

We have 60 years of data on how the human body behaves in 0g (space) and 1g (Earth). We have almost nodata on anything in between. The Moon has 1/6th of Earth’s gravity (1/6g), and Mars has 3/8ths (3/8g).

This is a massive unknown. Will 3/8g be enough to prevent bone loss and muscle atrophy? Or will astronauts on Mars still need to do 2.5 hours of ARED workouts every day? If so, how do you design a squat rack for a partial-gravity environment? How does the inner ear adapt? Will astronauts be able to walk normally, or will they adopt a “loping” Apollo-style gait? The Artemis program and the Lunar Gateway are not just about “flags and footprints”; they are essential human factors testbeds for learning to live and work in a partial-gravity world before we commit to Mars.

Closed-Loop Life Support

For a three-year Mars mission, you cannot pack all the water, oxygen, and food needed. It’s simply too heavy. The mission must use a “closed-loop” system, recycling everything. The ISS water recovery system is already 98% efficient, famously turning urine and humidity into drinking water (“yesterday’s coffee is tomorrow’s coffee”).

But a Mars system must be even better and, more importantly, 100% reliable. The human factors component here is maintenance. These are complex chemical and mechanical systems. They will break. Can a non-specialist astronaut, stressed and fatigued, repair a urine processor or a CO2 scrubber using a 3D-printed part and instructions from a screen? The design of these internal systems – their accessibility, the tools needed, the clarity of the repair procedures – is a life-or-death human factors challenge.

Growing food will also be part of this loop. Experiments like Veggie on the ISS have shown that astronauts can grow small amounts of lettuce. The human factors benefit is twofold: it provides fresh food (a source of vitamins and morale) and it offers a psychological connection to Earth. The simple, repetitive act of gardening and seeing something green and living in a sterile environment is a powerful stress reducer.

Summary

Spaceflight human factors is the science of keeping humans alive, healthy, and productive in an environment that is actively trying to harm them. It is the bridge between the human and the machine. This field has moved from simply ensuring survival to optimizing long-term performance.

It studies the body’s adaptation to microgravity – the fluid shifts, bone loss, and muscle atrophy – and engineers complex countermeasures like ARED to fight back. It confronts the immense radiation of deep space, a hurdle that must be solved for any Mars mission.

It studies the mind, selecting crews for teamwork and resilience and supporting them through years of isolation, monotony, and the stress of total autonomy. It uses analog missions on Earth to understand the breaking points of a crew and to design for psychological health.

And finally, it is the discipline that designs the physical world the astronaut touches. It shapes the cockpit from a wall of switches to an intelligent glass display. It designs habitats that are not just shelters but homes. And it builds the spacesuit, a personal spacecraft that enables exploration, even as it fights the human body with every movement.

The “human element” is not a weak link to be engineered around. It is the most adaptable, resilient, and creative computer on the mission. The entire purpose of spaceflight human factors is to design a system that unchains this human potential, allowing us to not just visit other worlds, but to live and work in them.