airlock

An airlock is a chamber used to transition between environments that have different pressures, atmospheres, or contaminants, such as a spacecraft or submarine and the outside environment. It is designed to minimize pressure loss and contamination during door openings and closings.

Most airlocks employ a two-door arrangement: an inner hatch connected to the habitable space and an outer hatch that leads to the external environment. The inner and outer doors are not opened at the same time. The airlock can be depressurized or repressurized, or its atmosphere can be purged, to match the pressure of the space beyond. Operators or crew members enter the airlock, seal the appropriate door, and then adjust the pressure before opening the other door. In space operations, crew members typically wear spacesuits during external activity.

Airlocks are used in spaceflight and in submerged or terrestrial facilities that require controlled exchange between environments. On spacecraft and space stations, they enable extravehicular activity without exposing the entire vehicle to the vacuum of space. On submarines and underwater habitats, airlocks manage passage between pressurized interiors and the surrounding water or air, helping control contamination and maintain safety.

Safety and design considerations include strict door sequencing, pressure equalization procedures, and redundant seals. A failure in the lock can lead to rapid pressure loss or contamination, so alarms, interlocks, and emergency procedures are common. The concept has been central to human spaceflight and undersea operations since the mid-20th century and remains a core element of life-support systems.