If humans are going to go to Mars, or mine asteroids, then recycling is going to matter. And that means recycling everything - including human waste. NASA has put some effort into solving the problem, because recycling is such an essential part of building a spaceship that can get people to Mars or anywhere else.
From article, (
First a few facts about human poop. A healthy person produces about 128 grams of feces per day, or about 46.7 kilograms (102 pounds) in a year, according to the medical literature. For a mission to Mars that might last two to three years, a crew of six (as posited in The Martian) would generate 300 pounds of feces each.
In the Apollo era, the toilet was a plastic bag attached to the astronauts’ butts with an adhesive. Urine was collected with a condom-like device and vented to space. Famously — or infamously — the last Mercury flight in 1963 actually suffered system failures because the urine collection bag leaked. Clearly, the bags didn’t work. Floating human waste is also a health hazard, since one can inhale tiny bits of urine or feces as they float around.
Enter Don "Doctor Flush" Rethke, a retired engineer from Hamilton Standard, now UTC Aerospace Systems. Rethke goes way back with NASA; he worked on life support for the Apollo 13 mission. He designed a commode that takes in urine and feces separately. It used suction — essential because in zero-g, liquids turn to spheres and float around, and solid waste won’t just fall into the bowl. Urine was collected in a cup-like contraption, while the solid stuff was sucked into a container and exposed to the vacuum — effectively freeze-dried and compressed. "We called them fecal patties," Rethke says.
A variation of his design is on the International Space Station, with two big differences: one is that the urine is now treated so that the water can be removed and reused, and the other is that the new system doesn’t freeze-dry the feces. (The ISS recycling system also takes in moisture from the air, which is largely astronauts’ sweat and exhalations.)
As for the solid waste, during the shuttle era it was just brought back. On the ISS, it’s stored in plastic or metal containers. When those fill up, astronauts load them onto a used Russian Progress vehicle, unlock it from the ISS, and let it fall to Earth to burn in the atmosphere, along with the rest of the ISS’s garbage. (Think of that the next time you see a meteor shower.)
Weird as it may sound, poop may provide good radiation shielding. In space, there are two sources of ionizing radiation that could harm astronauts. One is the background of galactic cosmic rays (or GCR). The other is a solar storm, known as a "solar particle event" or SPE. Both consist of charged particles, mostly protons.
These sources of radiation are less of a problem for ISS astronauts because they are still inside the Earth’s protective magnetic field. But once astronauts leave that field, the SPE could cause acute radiation sickness, while cosmic rays increase the risk of cancer.
The most efficient shielding is solid hydrogen because the element more easily deflects flying particles. But solid hydrogen isn’t available outside of a gas giant, and liquid hydrogen is difficult to handle, needing high pressures, cryogenic temperatures, or both. The next best thing is water, which has lots of hydrogen in it, or polyethylene.)
Me, "I found Polyethylene an interesting idea, as shielding, because basically this is the most common plastic. It is found commonly in grocery store plastic bags. It's not inconceivable on the Moon to use CO2 from Astronauts breathing, certain bacterias that would break down feces into CO2 and use CO2 and water from the Moon to create plastic. This plastic would then be used to coat many layers over a moonbase that would shield astronauts from the sun and cosmic radiation. You would need a good size astronaut population to breath out CO2 and create a lot of Feces but it is not impossible. This process would be easier on Mars, because along with the natural human produced CO2, Mars also has a lot of CO2 in its air. Add CO2, water, and a metal catalyst, and it's even easier to produce Polyethylene for solar and cosmic shielding."
From article, (Metal shielding like lead, which provides good protection against gamma and X-rays, is actually worse than no shielding at all, because the protons hit the atoms in the metal and create cascades of other particles, creating even more harmful radiation.
Jack Miller, a nuclear physicist at Lawrence Berkeley National Laboratory, along with Michael Flynn and Marc Cohen of NASA’s Ames Research Center, conducted an experiment funded by a grant from NASA to see how well human waste would work as radiation shielding. He and his colleagues couldn’t use real feces; instead they used a simulated poo made out of miso, peanut oil, propylene glycol, psyllium husks, salt, urea, and yeast. The goal was not to exactly duplicate the actual chemicals in feces; they wanted something roughly like it that held water and absorbed radiation and particles similarly.
They put it in a particle beam to see how well it absorbed the energy of flying protons. The beam was about as energetic as particles typically found in space. The fecal simulator absorbed a measurable amount of the energy, and the team found that the thickness matters. Too thin and the problem gets worse for the same reason that metals are bad shielding — the spaceborne particles make cascades. However, they were able to calculate that a fecal shield about 8 to 11 inches thick would cut down the radiation dose a lot. That was a good result, though Miller noted that the situation is more complex.
Remember, there are two kinds of radiation in outer space: the SPEs and the background radiation from cosmic rays. Cosmic rays carry five times as much energy as SPE particles do, and they’re the ones that can increase the risk of cancer. (NASA rules say the increased risk to astronauts shouldn’t be more than 3 percent above the general population.) The fecal simulator wasn’t as good at stopping those, but that was expected. "The energy of GCR is so high it will punch through just about anything," Miller says. "So you try to balance getting the risk as low as reasonably achievable.")
Me, "While interesting in a way of figuring out what is presently done with human waste, and, how can be used as a space radiation shield. I still feel that Polyethylene is a resource that should be looked at furthur for Moon, Mars and beyond bases. We have a fairly good idea how to make it, and how to apply it. All we need now is maybe a 3D printer to apply it. With this material we may not have to live underground. We just need a fairly good source of CO2, Hydrogen, and a metal catalyst. to produce the plastic."
From Google, (
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(ethylene)) is the most common plastic. The annual global production is around 80 million tonnes. Its primary use is in packaging (plastic bags, plastic films, geomembranes, containers including bottles, etc.).)
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