Gone are the days when Fred Haise, of the Apollo 13 crew, could remark on how his urine looked as if a golden string of glittering stars as they passed out of the evacuation chamber of the space capsule in which he'd just relieved himself. Or at least gone are the days when Bill Paxton in the character of Haise could say something like that in a movie and be accurate. These days our astronauts drink the water recycled from their pee -- and find clever new uses for their poop too.
On the International Space Station, they use an automated system to remove extract water from waste for use once more. On the private Mars shot that will launch in 2018, Inspiration Mars, they will use a simpler, but perhaps more elegant, method: a technique called forward osmosis. Water likes to move to diffuse concentrations whenever possible from high to low, in an effort to even things out. So when it's confronted with a solution that contains a solution with a high concentration of salt, which has a high osmotic potential, this ticks water off and it will move toward that higher concentration to balance things out. So when urine, which contains lots of water, of course, is put into in a chamber it will pass through the membrane, leaving behind all of the other stuff that makes up urine, leaving the water purified and the salty solution diluted and ready to, yick, drink. I'm sure that any remnant salty taste from the diluted solution will provide the astronauts plenty of reminder of where their water came from (their pee).
The forward osmosis method was tested on the last space shuttle flight, Atlantis in 2011. The problem is, the results showed that in microgravity osmosis worked at only about half the efficiency it does here on Earth, something the mission's engineers will have to work out. The Inspiration Mars people recently announced that these bags of water and waste will be used in an entirely novel way, to line the space capsule to protect it from cosmic rays.
A quote from a mission member in a New Scientist article on the subject points out that nuclei block cosmic radiation and that water has about three times the amount of nuclei that are found in metals. And since the nuclei block rather than absorb radiated particles, the water won't become irradiated, keeping it safe to drink. So lining the capsule with bags of water that the crew can also drink should be an efficient and elegant solution to both staving off cosmic radiation and dehydration among the crew.
But what's more efficient than drinking the water extracted from your own urine? Nothing. When a bag of water is finished off by the husband/wife team that will serve as personnel on the mission, they will use said bag to deposit waste. The osmotic processes will then extract the water for reuse. In the meantime, that bag of waste will go back in the capsule lining to serve as a shield once more, this time filled with poop or pee. And one can only imagine how effective those are at reflecting cosmic rays.
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