These are mentioned in tabletop science fiction RPGs such as Traveller and GURPS Space. In real life, portable airlock systems usually come in kit form and are designed for use in clean-room medical, research, and manufacturing facilities. Space-borne portable airlocks would only be distantly related to these devices, and be far more extensive and advanced.
Documentation online and elsewhere involving this speculative technology is sparse; most of this article is conjecture on the part of the author.
Portable airlocks are meant to gain access to a ship, space station, or base whose atmospheric integrity has been compromised. They may otherwise be employed when other entry options into such structures are not available or practical, and maintaining atmospheric integrity within is desirable. In some rare circumstance, they may also be used to pressurize an enclosed area previously exposed to vacuum, such as a cave on a vacuum world like the Moon.
A portable airlock may be affixed to any breach on an outer hull/bulkhead that is smaller than itself. They may also be used as an extension on an existing airlock if the latter is compromised. They may be inflatable, using the same technology as pressure tents, they may be collapsible and modular for quick assembly, or they may come in kit form.
When fully assembled or inflated, the airlock will essentially be a small portable room with doors on opposite sides. Their overall configuration may be square, rectangular, cylindrical or spherical, depending on the exact design. The side meant to be attached to the hull would have its outer frame project out ahead of it from several inches to several feet. The frame’s leading edges would be pliable and moldable, able to compress or stretch at every point as needed to form a tight fit on the target surface. It may be made magnetic for better grip on metal surfaces.
Once put into place, one or more astronauts would use epoxy or a welding torch to make sure the seal is airtight. Very advanced portable airlocks may be self-sealing through various techniques, such as rapid-hardening expansion foam around the seals.
Once in place and sealed, the airlock is ready for business, and will function like any other of its general design. Since the portable airlock will usually be carried by a vehicle of some kind, umbilicals to the ship can supply the breathing air and other essentials. If not, the airlock may need to use attached gas tanks and its own dedicated life support system and power supply.
To save on interior workspace, the airlock may eschew swinging pressure doors in its design and instead use either sliding panels, iris valves, or zipper locks. This may be essential as repairing or maintenance work on the spot may require extensive work.
Portable airlocks may also be used to help pressurize enclosed areas previously exposed to vacuum, such as natural caves and caverns, but also abandoned or damaged buildings with large breaches in them. In these cases, a wall of airtight material would be built up around the airlock in the breach and its sides sealed tight to this new barrier.
These are mentioned briefly in an equipment supplement of the 2300AD tabletop RPG. They are a logical extension of portable airlock technology and are meant for large scale maintenance and repair of spaceships and space stations.
These essentially amount to what are large, modular, multi-room extensions designed for use with portable airlocks. They would be stored either as collapsible modules or come in kit form. Sometimes hull breaches, or sections of a ship or station to be serviced, may be too large for a single portable airlock to fit over. These modular hull enclosures would come in sizes large enough to accommodate from two to a dozen or more personnel. They would be designed to be fitted together to form an enclosed volume large enough to cover the breach or bulkhead section in question. Like with a portable airlock, they would have moldable side sections which would allow their frames to conform with the irregularities of the hull. The individual modules may also be built up vertically as well as horizontally, to accommodate large hull structures, such as antennae or turrets.
Once assembled, a portable airlock would be attached and the entire assembly sealed to the bulkhead by torch or epoxy. Interior walls may be added or removed as needed. Once in place and fully pressurized, the Modular Hull Enclosure would allow crews to work on the exterior of a craft or station in relative work sleeve comfort.
These devices’ main purpose is to allow relatively quick boarding of a hostile spacecraft or stations. The crews of such facilities would be almost sure to heavily fortify or booby-trap their regular airlocks in anticipation of a boarding, making passage through them for invading troops very hazardous.
The boarding force may use a portable airlock instead to create their own entryway at some other point on the ship and bypass such traps. However, attaching a normal portable airlock and cutting their way in via torch may be too slow and give the interior crew a chance to set up traps or ambushes at the new breach point.
Military Portable Airlocks would be designed to anchor itself to the hull and seal itself to it as quickly as possible. For this reason, instead of just using magnetic clamps or epoxy, it might use explosive or super-heated bolts to drive the anchors into the hull in less than a second, and then use a self-sealing technology such as rapid-hardening foam to form an airtight seal just as quickly.
As soon as the portable airlock was in place, tamped charges would be placed on the hull (if they weren’t already in place on the leading face of the airlock) and blown, creating an egress into the ship big enough for troops to enter. When the charge is blown, the airlock would remain open to channel the force of explosion that doesn’t go into the hull back out into space. Obviously, the interior of the airlock would have to be as well-armored as the exterior for this.
However, as soon as the detonation is cleared and the interior atmosphere begins to vent, the airlock doors lock shut automatically, preventing any significant decompression. Troops can then start cycling through the airlock, either from space or from a troop carrier that may dock with the airlock unit. Total time from hull contact to the emergence of the first boarders onto the ship could be less than one minute in an optimal case.
Since this type of airlock is meant more for speed than for resource conservation, it probably wouldn’t bother with a full air evacuation cycle within its volume. While Military Portable Airlocks may have such functions available for occasional non-combat use, most likely it will simply vent its contained air into space every time its outer door opened to facilitate the quick cycling of troops.
http://en.wikipedia.org/wiki/Airlockhttp://www.daviddarling.info/encyclopedia/Q/Quest_Joint_Airlock.html http://www.seacorp.net/simplexp/cleanroom_airlock_enclosure_systems.htm http://traveller.wikia.com/wiki/Portable_Airlock
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