• Question: how does the ISS (iternational space station) balance the level the CO2 and O2 so the astrounats

    Asked by ALEX TUCKETT to Simon, Julia, Delma, Andrew, Alex on 9 Dec 2015.
    • Photo: Andrew Winnard

      Andrew Winnard answered on 9 Dec 2015:

      There is a complicated life support system that puts oxygen into the air while scrubbing co2 out.

      Most of the station’s oxygen comes from a process called “electrolysis,” which uses electricity from the ISS solar panels to split water into hydrogen gas and oxygen gas. There are also oxygen tanks 🙂 Carbon dioxide is removed from the air by a machine on the Zvezda Service Module based on a material called “zeolite,” which acts as a sieve, filtering the CO2 out.

    • Photo: Simon Challis

      Simon Challis answered on 9 Dec 2015:

      Great question 693nch28!

      The air on the ISS is more or less the same composition as that on Earth with around 78% Nitrogen, 20% Oxygen and about 0.05% Carbon Dioxide.

      The Oxygen and Nitrogen on ISS is mostly replenished with supplies from Earth (although some Oxygen is chemically generated/regenerated) but perhaps surprisingly the main issue on the ISS is not to run out of Oxygen by the crew, since we typically breath out most of the Oxygen we breath in (so the O2 levels drop slowly) but to control the build up of CO2 in the atmosphere. This is important because CO2 is a very toxic gas in large concentrations which can affect peoples health or even kill them.

      In order to remove excess CO2 in the ISS atmosphere a device on-board ISS is used called CDRA: Carbon Dioxide Removal Assembly which works by passing cabin air through a series of filters which chemically trap the CO2. The filters have to be routinely replaced once they become saturated with C02.

      You can learn more at the following links:

      – https://en.wikipedia.org/wiki/ISS_ECLSS
      – http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050210002.pdf

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