Background Information

In addition to having sufficient nutritious food, long duration space travelers will also need to have several other very important needs satisfied.

They will 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 which 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. Since many of the essential elements required for our comfort, such as air (suitable for humans) and water, are relativity scarce once we leave the planet Earth, we will have take some of these supplies with us.

When we decide to take food, water, and air from the Earth into space we are faced with a huge problem. It is extremely expensive to take supplies with us. To spend more than a few weeks in space we must either stay very close to home so we can frequently resupply the astronauts from the Earth (as we do in the case of the International Space Station), or we must develop very efficient methods of growing food in space and recycling water and air.

In this project we will construct two simple Martian habitats suitable for an extended stay on the surface of Mars or a long term space voyage. In both cases the emphasis will be on maintaining a comfortable breathing environment. 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 will consume oxygen and produce carbon dioxide.

Carbon dioxide is toxic, even at fairly low concentrations, so it is very important that excess carbon dioxide be removed from the air, and the consumed oxygen be 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 bonds created by Van derWaal's forces. Because the bonding forces are weak, adsorption is an easily reversible process.

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, generally speaking, not an easily reversible process.
In this project 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 project has a surface area equivalent to full sized rural market garden farm. Of course you can't plant crops on this surface, but it will 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.

Notes

This is a somewhat ambitious project, designed as a class demonstration, rather than as individual student projects. Students will construct the habitats as a class but keep individual observation journals.