Life in orbit necessitates a complete re-engineering of even the most fundamental daily routines. Maintaining personal hygiene remains an important part of health and psychological well-being during long-duration space travel on platforms like the International Space Station. The simple terrestrial act of brushing one’s teeth instantly becomes a complex challenge when gravity no longer dictates the behavior of water and paste. Astronauts must employ specialized techniques and materials to ensure cleanliness without creating a mess in the closed environment of the spacecraft.
Understanding Fluid Dynamics in Microgravity
The primary difficulty in oral hygiene stems from the physics of fluids when the force of gravity is negligible. In microgravity, other forces become dominant, particularly surface tension, which causes water to naturally form spheres.
This strong cohesion means water does not flow as a stream but clings to surfaces or floats freely as wobbling orbs. Toothpaste or saliva, once expelled, would float away as a contaminated cloud of residue. This behavior makes conventional rinsing and spitting impossible, as any liquid released would immediately become a danger to the delicate equipment and air filtration systems.
The phenomenon of capillary action, where a liquid spontaneously rises into a narrow space, also plays a role. Liquids readily “wet” and stick to surfaces, adhering to the bristles of a toothbrush or the walls of the spacecraft interior. This tendency means a crew member cannot simply shake a toothbrush clean or rely on a liquid to drain away. These unique fluid dynamics require a complete shift in how astronauts approach the entire brushing process.
The Astronaut’s Brushing Procedure
The procedure for brushing teeth in space is a highly controlled process designed to minimize water use and prevent material dispersal. Astronauts begin by acquiring a small amount of water from a sealed drinking pouch or dispenser. They carefully apply just enough water to moisten the bristles of a standard toothbrush, often by touching the bristles to the water outlet or a floating droplet.
A small ribbon of toothpaste is then squeezed onto the wet brush. The toothpaste used is typically an ingestible formulation, meaning it is safe to swallow after brushing. This eliminates the need for the traditional act of spitting the residue into a sink.
The crew member then brushes normally, keeping their mouth closed to prevent paste or saliva from escaping. They brush for the recommended time, ensuring all surfaces of the teeth are cleaned. The foam and residue generated during brushing are absorbed by the toothpaste itself, which is formulated to be swallowed safely.
Once brushing is complete, the astronaut swallows the paste and the residue accumulated in their mouth. If necessary, a final small sip of water from the drinking pouch can be used to swish and rinse the mouth, and this water is also swallowed. This method conserves the precious water supply and keeps the microgravity environment clean.
Managing Waste and Residue
The primary method of waste management is the consumption of the edible toothpaste and residue. By swallowing the material, the astronaut prevents the creation of liquid waste that would need to be contained and processed. This direct ingestion is the most efficient way to manage the bulk of the used product.
The remaining residue is contained and collected using absorbent materials. After swallowing, the astronaut must clean the toothbrush thoroughly. They often use a small amount of water, either sucking the excess moisture off the brush or wiping the bristles with a tissue or dry towel.
Any tissues or wipes used to clean the brush, along with the empty toothpaste tube, are considered solid waste. This solid waste is compacted and placed into designated waste containers on the station. These containers are later loaded onto resupply vehicles, which burn up upon re-entry into Earth’s atmosphere, safely disposing of the accumulated trash.