Now now, before you say it wont work, i know it wont. But its cool Now, we know humans produce Co2 right? Manned spacecraft just dump it. But, what if, it could be used as propulsion? According to a study by the United States Department of Agriculture, an average person's respiration generates approximately 450 liters (roughly 900 grams) of carbon dioxide per day.. Then times three or four people. This is 1800 liters of CO2 every day. What if it could be used for the Reaction Control System on a spacecraft? This has advantages and dis-advantages: 1. Cheaper RCS and lighter tanks 2. refuel naturally, while in flight! HOWEVER: 1. Since CO2 is not as dense as the regular fuel, it will be slower to turn. But the spacecraft would still have a backup tank and re-entry tank full of the usual fuel. DISCUSS!