This is the second in a series of articles that examine the real-life systems aboard the International Space Station (ISS) which inspired the fictional equipment found in Andy Weir's novel (and soon-to-be-released movie) The Martian. In the first installment, we looked at the many ways in which water is conserved and recycled. This time around, we will investigate the components that process air to make the ISS both habitable and comfortable for the humans inside.
Before getting into too much detail about the air systems on the ISS, a brief overview of the general layout is probably warranted. As with the water systems, many of the US-made air management components on the ISS have foreign counterparts. For the sake of simplicity, this article will focus only on the US equipment.
The habitable areas of the ISS are pressurized modules that are typically cylindrical in shape. Three node sections (named Unity, Harmony, and Tranquility) serve as the crossroads for all of the modules No matter which direction you choose to exit a node, your path will soon reach a dead end in some module.
On Earth we have the luxury of myriad natural processes that create air currents on a local and global scale. This helps to ensure that the same patch of air never lingers over any location for very long. In the manmade ecosystem of the ISS, however, such air flow does not occur naturally. The Intermodule Ventilation system (IMV) compensates by using fans to force airflow between the modules. Without it, the air would stagnate in those dead ends. Well, everywhere, actually.
The inter-module airflow is extremely important because the life support systems that manage the composition of the air are not present in every module. In fact, most of the US-managed life support systems are located in Tranquility. IMV mixes and moves the atmosphere to ensure that the air quality in every module is homogeneous--or nearly so.