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In the past, we've discussed how astronauts relieve themselves in space, and even what can be done with their pee. But there's another, darker side of this story: astronaut poop. Right now, astroturds become a magical light show, in that they are ejected from the ISS to fall back onto the Earth and burn up in the atmosphere.

So you can think about that the next time you see a shooting star. But there are so many things we can do with poo! Waste is the enemy in matters of space exploration, and that includes the bounty our bodies give us.

So let's use it! Now, there is a caveat to this: obviously, all poop needs to undergo a great deal of processing before it can be useful to us. But there are tons of great poop processors out there, in the form of microbes!

Lots of microbes eat poop. They love it. And there's a bunch already in your poop; they're kind of responsible for poop's whole deal.

But a couple of special species of microbe eat poop and produce plastic. These microbes, Ralstonia eutropha and Pseudomonas aeruginosa, produce polyhydroxybutyrate, or PHB, for energy storage; similar to how we use fat in our bodies. That PHB is literally a biological plastic, and it can be collected, purified, and fed into a 3D printer.

Now, P. aeruginosa can cause pretty nasty infections depending on how healthy your immune system is, so astronauts probably don't want to culture it up in space. And while R. eutropha isn't pathogenic, it's still not the lab microbe of choice. That is E. coli.

It's about as safe as a microbe can get, provided you're working with a safe strain. We know it really well, and we've already grown it in space! Plus, it's easy to clone genes from other microbes into E. coli.

So that's what's being proposed by researchers at the University of Calgary: clone the PHB-producing genes into E. coli, and let them eat poop. In space. In addition to the bio side of the equation, the tech side has been fully developed, including a system to 3D print plastic objects using PHB from these bacteria.

So astronaut poop can become, say, replacement parts on the ISS, or building material if, or when, we settle on Mars. Speaking of settling on Mars, what are we going to eat when we get there? The answer is actually less gross than you think, given the general premise of this episode.

The plan is to once again feed our poop to some microbial intermediaries, but this time they're helping us make food. So while the astronauts aren't eating poop, it is involved in their food supply. But then again, we've been using manure as fertilizer for ages, so it's not that weird.

So the idea, from a paper published in 2017, is to take the raw waste, and mechanically process it into carbon dioxide and methane, plus some leftovers. Then, a microbe by the name of Methylococcus capsulatus eats the methane and produces proteins and fats, which we would extract and use as a nutritional supplement. Alternatively, to distance ourselves from the ick factor, we could feed it to other organisms, which we'd subsequently eat.

The authors of this plan propose feeding it to fish or grubs. And any water produced in the process can be captured and purified, so it's a really low-waste approach to your waste. The first two options are pretty reasonable, when you think about it.

They rely on some very well-tested and clear principles, even though the applications sound a little sci-fi. But what if we just went full sci-fi for a minute? Because I've got to tell you about Water Walls.

These are hexagonal bags attached to the walls of a spacecraft that are networked to produce a full life-support system. Using poo. There's a bag for initial waste processing, for growing algae to eat, for water purification, for humidity and climate control, for fuel production.

It's got everything. And it's a pretty simple setup: the bags start with a soup of all the chemicals and microbes needed to do their jobs, and the end product from each bag gets sent to the next bag in the network through a filter. The crew provides the raw material.

And then the bags line the walls of your spacecraft or habitat, the ISS, your Mars ship, your moon pod, whatever, to provide radiation protection. Water makes a good radiation shield because it has a fairly low molecular weight. Heavy molecules basically just get in each others' way and limit how well they can absorb radiation, so the lighter the better.

That said, water is pretty dense, so a pure-water shield would weigh too much to be practical, but water plus chemical soups plus the bags containing them is a totally viable setup. This may sound like it comes straight out of Star Trek, but it's been in development at NASA's Ames Research Center for a long time, and was even slated to fly on a private, long-term Mars mission. But that mission was Inspiration Mars, in which noted rich-guy-who-likes-space.

Dennis Tito wanted to send a married couple to fly around Mars, but never land. This mission did not happen for a number of reasons, including NASA not dropping everything they were doing to help out a random multi-millionaire. Not even fellow rich-guy-who-likes-space Elon Musk was willing to throw money at the venture.

But while the mission may have been somewhat ill-advised and ultimately never took off, the Water Wall technology is actually viable. NASA has even made it available for licensing, so companies like SpaceX can take advantage of it in private space enterprise. And there you have it.

In space, you use everything at your disposal, and we mean everything, to make the mission a success. Including stuff you've already disposed of. Fortunately, you don't have to jump through so many hoops to design a great website.

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