Image from Steve Bowers
An airwall can be used as an easy-access airlock for spacecraft
An airwall is a hitech application of mesoscale technology, allowing two locations with different air-pressure or composition to be separated by a wall which will retain atmosphere, while allowing a macroscopic object (such as a person) to pass through unhindered. This technology allows an airlock on a spacecraft or habitat to be open to vacuum without loss of air-pressure, or allows two regions with different atmospheric pressures or composition to exist in proximity while allowing objects to pass through the barrier.

An Airwall consists of is a sheet of connected mesobots (more rarely nanobots) several centimeters thick for redundancy. The mesobots extend interlocking membranes which prevent gases from passing through, and can hold an atmosphere against the vacuum of space while allowing properly suited people or other permitted objects to pass. The Airwall employs a system of autonomous processors to communicate with compatible processors in the outer layer of a spacesuit or object. The effector mesobots recognize the processors in the suit/object as being authorized to pass and move aside while maintaining a seal to prevent air loss. The process of passage is fairly slow, but faster than waiting for an airlock to cycle; passing through an airwall is often compared to walking through a layer of stiff jelly. Airlock doors are still used to close the portal when the airlock is not in use, to protect against radiation, micro-meteors and prevent the slow leakage of gases.

A large, thick airwall can be used to seal a hangar or hatchway into a spacecraft's interior, and programmed to allow smaller craft to enter and exit with minimal airloss.

Airwalls can be considered to be a form of specialized and rugged utility fog. Their strength is approximately that of thick wood - a bioid or vec can lean on the airwall, but high velocity projectiles will go through it and a ramming vehicle will break through and likely damage it.

Many orwoods and other dyson tree types use airwalls to cover part, or all, of their structure and foliage. Specialised airwall foglets are used in Niven Cloud or Smoke Ring megastructures to prevent atmosphere loss.

Note that a typical airwall does lose some air pressure when a large object passes through, but not significantly more than any other airlock system. Airwalls may allow traces of atmosphere to seep from one side to another, so are not generally suitable for separating poisonous or highly corrosive atmospheres from locations where bionts or delicate machinery are present.
Image from Copyright Richard Patterson
This citizen zar is surrounded by an airwall, which maintains a comfortable atmospheric pressure far above ground level
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Development Notes
Text by Todd Drashner, extra notes by Anders Sandberg and Steve Bowers
Initially published on 10 September 2001.