Can Poop Fuel an Astronaut’s Return to Earth?

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Two University of Florida researchers have shown that astronauts' human waste can be used as the fuel that would bring their spaceship back to Earth.
Two University of Florida researchers have shown that astronauts’ human waste can be used as the fuel that would bring their spaceship back to Earth.

While I am a huge fan of every nation’s space program, I don’t think very much of manned spaceflight under current technology. In brief, there isn’t much for people to do in space that hasn’t been done already; robotic probes accomplish far more for vastly less money and keeping humans alive in space is a hugely expensive and risky proposition.

Recently, some scientists came up with a use for all the human waste that would come from opening a base on the moon and keeping it occupied for five years. University of Florida researchers Abhishek Dhoble and Pratap Pullammanappallil have shown it could be converted to methane and used to bring the moon-crew (lunatics?) home. It doesn’t solve all the problems of manned flight, but it does resolve one particularly tricky issue.

On short flights, the human waste issue isn’t really an issue. The human droppings go into containers which are loaded into capsules that burn up during re-entry to Earth’s atmosphere.

Or as Apollo 9 astronaut Rusty Schweickart put it, “one of the most beautiful sights is a urine dump at sunset, because as the stuff comes out and as it hits the exit nozzle it instantly flashes into ten million little ice crystals which go out almost in a hemisphere, because, you know, you’re exiting into essentially a perfect vacuum, and so the stuff goes in every direction, and all radially out from the spacecraft at relatively high velocity. It’s surprising, and it’s an incredible stream of … just a spray of sparklers almost. It’s really a spectacular sight. At any rate that’s the urine system on Apollo.” And that’s probably more than any of us wanted to know about astronaut pee in the 1960s.

However, if NASA were to put some scientists on the moon for five years, as is planned starting in 2019, there’s going to be a lot of stuff up there that can’t stay (the rules say we leave things pristine). Shipping it back to Earth would hugely increase the mass of any returning vessel, making the whole project more expensive owing to greatly increased fuel requirements.

Dhoble and Pullammanappallil have developed an anaerobic digester process, which means microorganisms break down organic material without any oxygen present. Their process results in methane and carbon dioxide. The carbon dioxide can be vented because, in the low gravity of the moon, it will simply dissipate into space. Meanwhile, the methane (290 liters per crew member per day) can replace the more conventional hydrogen and oxygen fuel used in rocketry.

To get the crew home, the methane would have to provide enough of a kick to accelerate the spaceship to 5,321 miles per hour, the moon’s escape velocity. Once the ship reaches that speed, Newtonian physics takes over, and the thing in motion will stay in motion. Unlike a car on Earth where there is friction, you don’t need to keep your foot on the gas in space. There will have to be enough methane after blast off to put the craft into a re-entry pattern, but this is a minor adjustment. The trick will be designing a ship that can reach that speed with the methane available.

Additionally, the process can generate 200 gallons of non-potable water per year. Electrolysis will split the H2 from the O, and the crew will have a back-up oxygen source. The hydrogen can be burned as fuel, but will need oxygen to ignite, making it a dubious source of energy to get back home.

Obviously, this process will have applications back on Earth. Seven billion people means a lot of methane if we choose to harvest it.

So now I have one less reason to oppose human spaceflight, which only leaves a few hundred.

Jeff Myhre is a contributing journalist for TheBlot Magazine

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