|Posted by Rohvannyn on November 2, 2015 at 9:35 PM|
Another approach to addressing CO2 and water vapor in cabin air is a series of reactions discovered by the French Chemist Paul Sabatier during the early years of the 20th Century. In this chemical process hydrogen is reacted with carbondioxide at about 480 degrees F, to yield methane (CH4) and water. The water can then be subjected to electrolysis to yield more hydrogen and free oxygen. The concept of Mars Direct, a plan for reaching Mars from Earth’s surface, is based on this idea.
In order to concentrate the cargbondioxide in our ship or station to make it available for recation, we’d either need to remove it chemically, driving CO2 off the chemical scrubbing agent (such as sodium or Potassium hydroxide) or we could chill cabin air down to dry ice temperatures to freeze out CO2 and moisture as well. We’ve discussed processes such as these in the biodyne article.
Four Moles of H2 (hydrogen gas) reacted with a mole of CO2 require about 320 thousand joules to yield a mole of methane and two moles of water. For a crew of six, we’d be looking at a constant power input of about 600 Watts to drive the Sabatier reaction at 100 percent efficiency. Of course we won’t get that but about 1,500 Watts should be safe. In situations that allow passing behind a planet or shading is available, low temperatures can be achieved by exposing a radiator to vacuum. Even with the “thermos-bottle effect” of space, a relatively few square meters of radiator can provide effective cooling for a small vehicle.
Methane itself can be broken down to yield free hydrogen and carbon graphite. This carbon can be stored as ashe or I suspect we will learn to synthesize carbohydrates from methane and a little oxygen. I suspect we won’t duplicate photosynthesis any time soon but if we can make sugars and starches from methane, through effective waste reduction technology we could continuously recycle air, water, and (most of our food) at moderate energy expense.
If we assume a recycling system in which water is cracked to yield hydrogen and oxygen, carbon dioxide is made to yield it’s oxygen while carbon is incorporated into methane and methane is reduced to pure carbon and free oxygen, we can also think about extracting additional oxygen supplies from asteroid rock. Hydrogen can extract oxygen from many sorts of minerals at high temperature, yielding pure metals and silicon as well as water vapor which can be cooled and cracked to extract oxygen. Some of the oxygen can be combined with the carbon graphite to produce carbonmonoxide (CO) which has been shown to be very effective in extracting metal from rock such as that making up many asteroids.
If therefore we can make our carbohydrates we can greatly reduce the amount of food we must ship to an orbital station or departing space mission while oxygen and water will be continuously recycled, without the need for extensive green house or algae tube arrangements.