Ammonia
Why exactly would you want a tank of Ammonia on your space station? Backup plan just in case the Russians try to take over?
Mission specialists Clayton Anderson and Rick Mastracchio (seen below) earlier today ventured outside the International Space Station on the first of three planned spacewalks for space shuttle Discovery's STS-131 mission. Rick Mastracchio exits the Quest airlock today. Pic: NASA TV The pair exited the Quest airlock at 05:31 …
I was unaware that astronauts need spend hours in a hypobaric chamber before space walks. The atmospheric pressure in the ISS is ~14 pounds/in^2, but the pressure in the space suits is only ~6 pounds/in^2, so they must spend a night at ~10 pounds/in^2 to avoid the bends.
So my idea of a spacewalk (throw on the old spacesuit and step outside) was complete rubbish.
They don't actually have to do the campout procedure, they used to just do a load of prebreathing of the right concentration of oxygen to purge the nitrogen from their blood, but have discovered that it's difficult to don the suit while maintaining this protocol (you can only breathe 'normal' air for a small period of time without having to start again etc), so the campout makes life much easier for them...