Colonel Panic wrote:I was surprised to read that 5 grams of oxygen would be enough to keep an astronaut (on Mars) breathing for 10 minutes. Seems a very small number to me!
A quick calculation (which may be wrong) says that 5 grams of oxygen is what you'll find in 110-115 liters of air on earth at sea level. It does sound like very little: if you'd be locked up in a room with 110 liters of air you would suffocate fairly quickly. But that's a lot to do with all the CO2 you expel. In a space situation you could probably make use of all the oxygen in the air.
Another way of calculating oxygen need would be to convert the energi needed per day (some 2 000 kcal) to the weight of the stuff being metabolized: fat and carbs, mostly. And then calculate how much oxygen is needed to burn that under ideal circumstances. My high school chemistry from forty years ago isn't enough for a quantative calculcation, but I can give it a go from a qualitative point-of-view:
Since the waste product CO2 contains 57% oxygen by weight, five grams of oxygen could not possibly metabolize more than 3-4 grams of carbon. And that's not even taking the H2O (89% oxygen by weight) into consideration; there's a lot of hydrogen in both carbs and fat. So let's say five grams of oxygen lets you metabolize 2 grams of food. There are 6*24=144 ten minute periods per 24 hours, so let's say 300 grams of food per day. To get to the 2 000 kcal per day in 300 grams of food, the food must contain some 667 kcal/100 grams. There are food stuffs that reach such level: hazelnuts and chicken fat, for example.
To survive on 5 grams of oxygen per ten minutes, you really need to have special diet and some clever means to use every single oxygen molecule. But the rough figures aren't off by an order of magnitude.
I would be happy if someone more knowledable would give it a go with an estimate!
Autocorrect is so frustrating. It's always making me say things I didn't Nintendo.