Humans cannot breathe in space due to the absence of a breathable atmosphere and the extreme conditions of the vacuum. Earth’s environment provides the precise balance of gases and pressure necessary for human life. Space, by contrast, presents a hostile environment where biological processes cannot function without specialized protection.
The Need for Oxygen
Oxygen is essential for human life, playing a central role in cellular respiration, the process by which cells generate energy. This energy, in the form of adenosine triphosphate (ATP), powers all bodily functions, including muscle movement, nerve signaling, and tissue repair. Without sufficient oxygen, cells must switch to a less efficient energy production method, leading to lactic acid buildup and potential tissue damage.
A severe lack of oxygen, known as hypoxia, can rapidly lead to serious consequences. The brain and heart are particularly susceptible to damage. Symptoms such as confusion, rapid heart rate, and difficulty breathing can manifest as the body struggles.
The Extreme Environment of Space
Space is a near-perfect vacuum, lacking atmospheric pressure. This extreme low pressure has profound effects on liquids and gases, including those within the human body. One significant consequence is ebullism, where the reduced external pressure causes bodily fluids to boil at normal body temperature.
Ebullism begins when the ambient pressure drops below 6.3 kilopascals (47 millimeters of mercury), a point known as the Armstrong limit, reached at high altitudes. The gases naturally present in the body, such as air in the lungs and dissolved gases in tissues, also expand dramatically in this low-pressure environment. This expansion can cause internal structures, like the lungs, to rupture if air is held within them.
How the Human Body Reacts
If an unprotected human were exposed to the vacuum of space, the body would undergo a rapid sequence of events. The air within the lungs would be expelled due to the pressure differential. Unconsciousness would occur quickly, within 10 to 15 seconds, as oxygen rapidly leaves the bloodstream.
Simultaneously, ebullism would cause water in the tissues to vaporize, leading to significant swelling of the body, potentially doubling its normal size. However, the skin is elastic enough to prevent the body from exploding. The continuous evaporation of water would also draw heat away, causing exposed moist areas, such as the nose and mouth, to nearly freeze. Survival in such conditions is limited to 90 seconds to a few minutes before severe damage or death occurs.
Protecting Astronauts in Space
To enable human survival and work in space, advanced technologies are used to counteract these extreme conditions. Spacesuits function as personal spacecraft, providing a self-contained environment, shielding astronauts from the vacuum, extreme temperatures, radiation, and micrometeoroids. These suits maintain a stable internal pressure and supply breathable oxygen, while also removing exhaled carbon dioxide.
The Portable Life Support System (PLSS), often integrated into a backpack, is a key component of spacesuits. It circulates oxygen, removes carbon dioxide using filters, and manages temperature through a cooling system. Inside spacecraft, Environmental Control and Life Support Systems (ECLSS) maintain a habitable atmosphere. These systems generate oxygen, remove carbon dioxide, and regulate air pressure, temperature, and humidity, creating an Earth-like living environment.