At the heart of planetary engineering is the Weyland Yutani APP or Atmospheric Processing Plant. Over a period of decades, a series of plants can convert a primordial atmosphere and make it fully breathable and suitable for human habitability.

The facility itself is ran on a 1TW fusion powerplant. The atmosphere is pulled in via intakes situated around the base of the structure, it is then accelerated to hypersonic speeds and injected into a fusion torus where it is heated to near plasma temperatures. The extreme heat causes molecules within the gas to dissociate into their component atoms which are then sorted by a series of magnetic fields into their constituent elements.

Some of these components, such as carbon, are drawn off as waste by-products, 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.

Although the plant is completely automated in its operation, it still requires constant maintenance. A small colony of several hundred workers is usually placed a short distance from each plant so that they can keep it easily serviced.

The plant itself is criss-crossed with maintenance catwalks and machinery floors. There are also roadways and cargo elevators large enough to drive heavy equipment in for repairs and replacements. Larger equipment is brought down from orbit already assembled and can be replaced by removing the outer panels of the plant and lowering them directly by crane into the depths of the facility.