Air

An Experiment on a Bird in an Air Pump depicts an experiment performed by Robert Boyle in 1660 to test the effect of a vacuum on a living system. Joseph Wright of Derby, 1768.

I'm reading The Warrior's Apprecntice by Lois McMaster Bujold. It's part of the Sci-Fi series starring Miles "I'm not a mutant" Vorkosigan. Normally these are great fun. This one is little rough, possible because it's one of the first. Anyway, we've got soldiers in armored space suits attacking enemy forces holed up in an asteroid mining complex in an otherwise uninhabited star system, which got me to thinking about air.
    Given our present level of technology, any kind of trip to another planet is going to take years, and if you are going to survive, you will need air. Carrying enough air to breath will not be a problem, I think we can handle that. The problem is if you have a leak. I'm reminded of the mysterious crash of the business jet in South Dakota a few years ago. Nobody knows what happened, but investigators surmised that the plane lost pressurization and everyone passed out before anyone realized what had happened. The plane continued to fly on autopilot until it ran out of fuel.
    There are two kinds of leaks. There are big ones that you can detect and presumably stop, and then there are little ones that are undetectable, except for the fact that you are constantly losing air pressure. For a long duration voyage the second one is the more dangerous. Given your rate of loss, do you have enough reserves to keep replenishing it for the next umpteen months or years? And what if you have an accident (or two) where you lose a big bunch of air all at once? Things could get very sticky. How would you like to wake up and discover you have enough air to last eleven months when you know your mission is going to last twelve?