A common and often humorous question about human physiology in space is: can astronauts pass gas? This inquiry, while seemingly trivial, involves genuine scientific and practical considerations for astronaut health and spacecraft habitability during prolonged missions.
How Gas Forms in the Body
Intestinal gas is a natural byproduct of digestion. One source is swallowed air, which can occur during eating, drinking rapidly, or talking. Most swallowed air is released through burping, but some travels through the digestive tract.
A more significant source of gas production stems from the breakdown of undigested food components by bacteria in the large intestine. Certain carbohydrates, such as sugars, starches, and fiber, are not fully digested in the small intestine. These undigested foods then move into the large intestine, where harmless bacteria ferment them.
This process yields various gases, including hydrogen, carbon dioxide, and, for about one-third of individuals, methane. While these primary gases are odorless, the unpleasant smell of flatulence comes from small amounts of sulfur-containing gases.
The Act of Passing Gas in Space
Astronauts do pass gas in space, as their digestive systems function similarly to Earth. The fundamental difference lies in how gas behaves in a microgravity environment.
On Earth, gravity helps separate solids, liquids, and gases within the digestive system, allowing gas to be expelled cleanly. In microgravity, this separation does not occur; solids, liquids, and gases mix and float together. This can lead to “wet burps,” where liquids or food particles are expelled with gas, which can be highly uncomfortable.
Once gas is released into the spacecraft cabin, it disperses freely. This happens more slowly than on Earth because air currents are limited to those generated by fans.
Health and Habitat Considerations
Intestinal gas poses several considerations for astronauts and spacecraft environments. For astronauts, trapped gas can cause discomfort or pain, as the usual gravitational cues for gas expulsion are absent.
The enclosed nature of a spacecraft also means that odors from flatulence can accumulate, leading to an unpleasant living environment. Astronauts have described the general smell of the International Space Station (ISS) as a mix of burnt steak, body odor, and antiseptic.
Beyond odor, the gases produced, particularly hydrogen and methane, are flammable. While the risk of an explosion from flatulence is very low, early space missions had concerns about this potential hazard in a confined, oxygen-rich atmosphere. The continuous presence of these gases, along with other human-generated contaminants, places a constant demand on the spacecraft’s air filtration systems to maintain air quality.
Managing Intestinal Gas for Astronauts
Space agencies and astronauts employ several strategies to mitigate the effects of intestinal gas. Dietary adjustments are a primary approach, with astronauts advised to avoid gas-producing foods before and during missions. Foods high in certain carbohydrates, such as beans, cabbage, and broccoli, are known to increase gas production.
While early missions explored very strict low-residue diets, current astronaut diets are more varied, though food choices still minimize discomfort and cabin air contamination. Regular physical activity also promotes healthy gut motility, which helps in the efficient passage of gas.
The spacecraft’s Environmental Control and Life Support Systems (ECLSS) are crucial for managing the cabin atmosphere. These systems constantly filter and purify the air, removing carbon dioxide, trace contaminants, and odors using various filtration technologies. This comprehensive air revitalization ensures a habitable and safe environment for long-duration space travel.