"That's the Atmosphere Processor?"
"Yep, that's it. Remarkable piece of machinery, completely automated. You know, we manufacture those, by the way."
Ripley and Burke, regarding the APP on LV-426 (from Aliens)

An Atmosphere Processing Plant on a terraformed world.

The Atmosphere Processing Plant[1] (APP),[2] also known as the Atmosphere Processor (AP),[3] Atmospheric Processor or Atmos, is a large automated reactor capable of "converting" an unbreathable, toxic or otherwise inhospitable atmosphere into one suitable for human habitation. Atmosphere Processors are a key component of extrasolar colonization efforts. The technology was pioneered by Weyland Corp in the first half of the 21st century[4] and was later developed and refined by the Weyland-Yutani Corporation.

While the conversion process is entirely automated, a constant crew is required to oversee an APP's maintenance. Often an entire colony will be established for this very purpose, such as Hadley's Hope on Acheron (LV-426).


"They set up massive atmosphere processing plants on suitable planets, do something to the air—clean it, treat it, I don't know, I'm a medic—and it takes decades."
Garcia to Ripley, regarding Weyland-Yutani's use of APPs (from Alien: Out of the Shadows)

The first planet to develop a breathable atmosphere through the use of such a device (then known as the Weyland Atmospheric Processor) was GJ-667Cc in 2039.[4] APPs are cone-shaped towers some 1,500 meters high and are powered by a 1.0 terawatt fusion reactor.[5] The conversion process they carry out starts when native atmosphere is drawn in through a series of levers in the base and sides of the structure. This gas is then drawn up through a battery of turbines, which compress and accelerate the atmosphere, into a series of hot mass processors arranged in a ring around the central fusion core. Within the processors, the gas is passed through a high temperature electrical arc that heats and ionizes it, before it is further heated to near plasma temperatures in the region of 5,000°K by magnetic coils.[5] The extreme heat causes molecules within the gas to dissociate into their component atoms.

Once reduced, the hot streams of monatomic gas are sorted by a series of magnetic fields into their constituent elements. Some of these components, such as carbon, are drawn off as waste by-product, many of which have value as fuel sources, industrial cleaning solvents or raw materials for manufacturing. The remaining hydrogen, nitrogen and oxygen atoms are expelled back into the atmosphere from the top of the processor to form as H2, N2 and O2.[5] Repurposing an existing atmosphere in this way is said to be preferable to generating a breathable atmosphere from scratch.[6]

While the APP's fusion reactor is liable to undergo catastrophic meltdown if critical systems are damaged, the resultant explosion, although enormous in scale, does not create any notable radioactive fallout.[7][8] Once stable atmospheric equilibrium is achieved, the processor continues to monitor environmental gas compositions and will automatically correct imbalances.

APPs are often used in conjunction with natural terraforming techniques, including the introduction of ecological architectures — usually through the use of specially engineered mosses, grasses and small flowering plants — that will convert certain atmospheric gasses (mainly carbon dioxide) into usable oxygen.[5]

Atmosphere Pressurizer

Sold exclusively in conjunction with Weyland Atmosphere Processors, the Atmospheric Pressurizer can create a locally adapted micro-pressurized environment to prevent injury, illness or discomfort on off-world colonies with either marginal or oppressive stratospheric hold. On most planets, a standard atmospheric pressure of approximately 1.0 atmosphere at sea level can be achieved, reducing the need for decompression treatments and additional medical personnel in the early stages of terraforming.

Behind the Scenes


For Aliens, the station's exterior was designed by Ron Cobb and constructed as a six foot tall miniature.[9] According to Steve Begg who did model effects on the film (uncredited), director and writer James Cameron also did at least 6 production drawings of the station.[10]


Location selection

The production team initially planned to film the Atmosphere Processor interiors in Aliens at an oil refinery, surmising that the complicated piping and ductwork would give them the industrial look they required. To this end, they went to scout a disused BP refinery on the Isle of Grain, east of London, but upon arriving discovered that the facility had already been demolished.[11] The situation was further complicated by discussions with the site's owners, who informed the crew that under no circumstances could pyrotechnics be used within the refinery due to the danger of fire, even at an disused facility.[11] Owing the the large part such effects would play in the film's Hive action sequences, the idea was abandoned and the crew subsequently began searching for disused power stations, of which London has several. The Atmosphere Processor sets were ultimately built at Acton Lane Power Station in west London, which Cameron liked because of the grilled walkways and stairways, allowing them to see the station's full height.[12]

Problems with Acton

After the location was selected, it was discovered that there were a few problems with it;[12] having not been used since its closure on October 31, 1983,[13] it was very rusty.[12] However, the biggest problem was that it was covered in asbestos, having been a coal-fired power station, forcing the production to spend a significant sum of money with asbestos mitigation to make it safe to film.[12] After the process was completed, they still had to take multiple air readings a day, discovering the quality of the atmosphere inside the plant was actually better than that in the sound stages at Pinewood Studios.[12] Despite this, many crew members continued to wear masks as a precaution, wary that traces of the carcinogenic substance may remain.[14] Once the location was cleaned, the interior was sprayed silver to match the futuristic aesthetic Cameron wanted.[15]

Another problem encountered at the location surrounded the use of the Colonial Marines's APC; the aircraft tug used as the basis for the APC was initially so heavy that it would have fallen through the floor of the power station and into its basement. Even after a significant amount of weight was removed from the vehicle, the building's floor had to be reinforced to support it.[12]

Set abandonment and rediscovery

After filming ceased, the set was essentially abandoned as it was; when the power station was later chosen as a filming location for 1989's Batman, where it stood in for the Axis Chemicals works, the crew discovered most of the Aliens set still intact inside.[12] Indeed, at several points in Batman, elements of the Atmosphere Processing Plant from Aliens are easy to make out, most notably during the shootout inside Axis Chemicals near the beginning of the film. In particular, the stairways that Ripley has to negotiate while searching for Newt are used by Jack Nicholson's character Jack Napier in Batman.