Background Information

Long duration space travelers will need to have a supply of nutritious food. However, they will also need the following:

  1. A suitable breathing environment. This means sufficient oxygen in a safe form (i.e. diluted with nitrogen), a comfortable humidity, and air free of other dangerous gases.
  2. An adequate and reliable source of water.
  3. A method of providing warmth.
  4. An environment that provides protection from cosmic rays and solar ultraviolet light.

Astronauts in a simulated experimental greenhouse on Mars

Figure 1: Astronauts in a simulated experimental greenhouse on the Martin surface. (Air-lock door removed)

To satisfy these conditions, space explorers of the future will need to live in space habitats specifically designed to provide a comfortable living environment. Many of the essential elements required for our comfort – including air and water – are relatively scarce once leaving Earth and will have to be part of our “package” of materials to accompany a long duration voyage. Taking these supplies – food, water and air – is very expensive. On the International Space Station, these supplies are frequently renewed by US shuttles and Russian Progress flights. Water for human consumption is recycled, but we will need water for growing food on long-term voyages.

This activity is an ambitious one; it is suggested that it be used as a teacher demonstration with individual student involvement in recording observations.

In this activity, we will examine the provision of breathable air on a long-term space voyage or on the surface of Mars by constructing simple Martian habitats.

One habitat will have full air recycling and the other habitat will have no air recirculation capabilities.

The focus is on recycling breathable air.

Once sealed into their spaceship, astronauts will be highly dependent upon recycling their air and water in order to conserve their resources. In a sealed environment air breathing mammals consume oxygen and produce carbon dioxide.

Carbon dioxide is toxic, even at fairly low concentrations. Excess carbon dioxide must be removed from the air, and the consumed oxygen replaced.

To reduce the carbon dioxide levels we will use activated charcoal. Activated charcoal removes carbon dioxide by a process called adsorption. Note that process of adsorption is not the same as absorption.

Adsorption is the process whereby molecules and atoms bond themselves to the surface of a material (such as activated charcoal). These bonds are generally quite weak and the adsorption process is easily reversible.

Absorption, on the other hand, is the process whereby atoms and molecules are incorporated into the bulk volume of a substance and may involve the formation of a solution. Absorption is not an easily reversible process.

In this activity we will use charcoal to act as an adsorbing medium to control excess carbon dioxide and water vapour in the habitat.

1 gram of activated charcoal has a surface area of between 500 and 1000 square metres.

A small jar containing 250 grams of ordinary BBQ charcoal represents a fantastically large adsorbing surface area, at least 125 thousand square metres (12.5 hectares!) Imagine this little simulated habitat that you construct in the activity has a surface area equivalent to full sized rural market garden farm. Of course you can't plant crops on this surface, but it can adsorb an enormous amount of carbon dioxide.

In our habitat we will use green plants to produce oxygen and to further reduce carbon dioxide levels in the air.