Reid: NASA wants to send humans to Mars, but it’s not going to be easy.   In addition to months of isolation, heavy doses of dangerous radiation, and the stress of doing basically the most risky thing ever -- you’re also not gonna have a lot of room.   So, what if astronauts could recycle their own waste into something useful?   NASA’s already working on perfecting 3D printing in space, so if astronauts needs a part or a tool, they can just print them instead of having to carry everything they could possibly need.   And now, they’re also sponsoring research into recycling human waste, like urine and carbon dioxide, into things like food and plastic.   We were curious about how that would work, so we got in touch with the researchers to learn more about what they do.   One of the projects, led by biologists at Clemson University in South Carolina, is looking to use genetic engineering to turn astronauts' urine and the carbon dioxide waste that they exhale into nutrients, like omega 3, and plastic for 3D printing.   But … in order to do it, they’re going to need a little help. First, from algae. Then, from yeast.   The plan is for astronauts to grow algae using energy from the sun, carbon dioxide, and nitrogen from urea, one of the main components of urine.   As it grows, the algae will produce lipids, a type of organic compound that includes fatty acids.   Those fatty acids, plus some more nitrogen, is the yeast’s favorite dinner, and the hope is that as it digests its food, it’ll break down all the lipids into different fatty acids -- some that can be used as nutrients for humans, as well as ones that can be used in chemical reactions to make a type of plastic for 3D printing.   But there’s a lot of chemistry and genetic engineering that has to go into making this work.   For one thing, they’ll need to engineer the yeast so it produces the fatty acids they want.    For example, right now the yeast makes a fat that’s close to omega 3, but not quite. So they’ll add genes that rewire its chemistry to include the reactions that make omega 3.   Then, they’ll engineer the yeast to make more of the fats, because right now they don’t make enough to be useful.   So the team will splice out the genes for processes that the yeast doesn’t really need to be doing in its job as a fatty acid factory, and replace them with genes that encourage it to make more of those useful fats.   Another one of the projects, led by researchers from Washington University in St. Louis, is also trying to make something useful out of human waste. But this time, they’re turning carbon dioxide into protein-based materials.   And they’re planning to use cyanobacteria to do it.    Cyanobacteria are great for space travel, because they don’t need much to live. Feed them carbon dioxide, and they’ll grow, even in extreme environments.   But there are challenges here, too.   The bacteria already make some kinds of proteins as they grow. But they’ll have to be engineered to produce the right kinds, and in a way that they’re stable and don’t immediately break down into something else.   Then, the cells have to be engineered to recognize the proteins as waste and excrete them, because normally they’d just break them down and use them for energy.   Once that’s done, the researchers will engineer the bacteria to make lots and lots of the proteins.   These projects are still in the very earliest stages. But someday, astronauts might be farming yeast and cyanobacteria for nutrients and plastics and proteins, all because they pee and breathe.   Thanks for watching this episode of SciShow Space, which was brought to you by our patrons on Patreon. If you want to help us keep making episodes like this, just go to patreon.com/scishow. And don’t forget to go to youtube.com/scishowspace and subscribe!