Aerospace physiology is the scientific discipline dedicated to understanding how the human body reacts to and adapts to the extreme and unique environments of high-altitude flight and space travel. The field investigates the physiological and psychological stresses imposed by non-terrestrial conditions, such as altered pressure, gravity, and radiation exposure. This research provides the foundation for developing the specialized equipment, procedures, and training programs necessary to ensure human safety, performance, and long-term health in aviation and spaceflight.
Defining the Scope of Aerospace Physiology
Aerospace physiology differs from general human physiology by focusing on conditions to which the human body is not evolutionarily adapted. The discipline is highly interdisciplinary, drawing upon principles from medicine, physics, and engineering to solve complex human-machine interface problems. Its focus is predictive and preventative, working to anticipate and mitigate potential health issues before they become problems.
The field is broadly divided into Aviation Physiology and Space Physiology, reflecting the two distinct environments studied. Aviation Physiology deals with conditions within the Earth’s atmosphere, such as high-altitude flight, rapid acceleration, and reduced atmospheric pressure. Space Physiology addresses the challenges of orbital and deep-space missions, including prolonged microgravity, vacuum exposure, and cosmic radiation. Both sub-disciplines share the goal of maintaining optimal human function in environments that are hostile to life.
Critical Environmental Stressors
The aerospace environment subjects the body to several powerful external physical conditions that define the field’s study. One of the most immediate stressors is altered atmospheric pressure, which drops significantly with increasing altitude. At sea level, barometric pressure is about 760 mmHg, but this falls dramatically at high altitudes. This hypobaric, or low-pressure, environment is the primary cause of physiological challenges in high-altitude flight.
Another major category of stress involves gravitational forces, which range from intense acceleration to the near absence of gravity. During launch, re-entry, or high-performance maneuvers, pilots and astronauts can experience high G-forces, sometimes up to nine times the normal force of gravity (9G). Conversely, during orbital flight, the body is exposed to microgravity, an environment where the constant mechanical loading of gravity is essentially removed.
The third major stressor in the space environment is radiation exposure. On Earth, the planet’s magnetic field and atmosphere provide a natural shield against these high-energy particles. Outside of this protective layer, the risk of damage to cellular structures and DNA from ionizing radiation increases significantly. Understanding the interaction of these stressors is central to designing safe aerospace missions.
The Body’s Response to Aerospace Extremes
The external stressors trigger a cascade of internal biological and physiological changes that aerospace physiologists must manage. Low atmospheric pressure at altitude directly leads to hypoxia, a condition where the body’s tissues do not receive enough oxygen. Because the partial pressure of oxygen decreases with altitude, an unacclimated person may experience impaired judgment and mental fatigue at relatively moderate altitudes.
Hypobaric environments also cause decompression sickness (DCS), which occurs when dissolved gases, primarily nitrogen, come out of solution in the body’s tissues and blood. This gas evolution forms bubbles when the surrounding pressure drops too quickly, causing pain in the joints, neurological symptoms, or pulmonary issues. The lack of a stable gravitational field in space creates dramatic fluid shifts, with blood volume moving toward the chest and head, leading to facial puffiness and a reduction in circulating blood volume.
Prolonged exposure to microgravity results in significant cardiovascular and musculoskeletal changes due to the absence of mechanical loading. Astronauts can lose bone density rapidly, primarily in weight-bearing bones like the hips and spine, despite rigorous exercise. Skeletal muscles, especially the anti-gravity muscles in the legs, atrophy rapidly. Furthermore, the vestibular system, which controls balance and spatial orientation, becomes confused by the sensory conflict of microgravity, often causing space motion sickness and post-flight orthostatic intolerance.
Practical Applications in Aviation and Spaceflight Support
The knowledge derived from aerospace physiology is directly applied to engineer protective systems and create operational protocols for crew safety. The design of life support systems, such as pressurized cabins and specialized oxygen equipment, is based on physiological requirements to counteract low pressure and hypoxia. This includes developing pressure suits and regulating the atmospheric composition to maintain a breathable and non-toxic environment.
A major application is in crew selection and training, where personnel are exposed to simulated environments to prepare their bodies and minds for flight. Centrifuge training is used to teach aviators how to tolerate and mitigate the effects of high G-forces, preventing G-induced loss of consciousness. Hypoxia training in altitude chambers teaches aircrew to recognize their specific symptoms of oxygen deprivation before their cognitive and physical performance is compromised.
To counter the long-term effects of microgravity and radiation, physiologists develop sophisticated countermeasures. These include specialized, in-flight exercise regimes to maintain muscle mass and bone density, often involving resistive equipment to mimic gravity’s load. Pharmacological and nutritional interventions are also studied to mitigate bone demineralization and protect against the long-term risks associated with radiation exposure.