It’s probably best if we all just come clean and admit that we’ve all thought about this at one time or another: if you were floating weightless, could you fart yourself into motion? I mean, your butt is basically just an integrated bio-ass rocket, right? As you’d expect, it’s more complex than you think, and real astronauts have tried it.

I mean, you’d think it should work, at least a little bit — farts are an outgassing of flatus from the body, and you’d think the basic Newtonian law of action/reaction should mean that the farter is pushed away from the fart material, resulting in some sort of propulsive motion.

Now, there’s no documented NASA study of FARTS (Fast Acting Rectal Transportation System) or anything like that, but there is an admission that informal tests have been attempted from retired Canadian ISS astronaut Chris Hadfield.

Hadfield was doing a Reddit AMA, when the topic of getting ‘stuck’ (floating in a module, and finding oneself unable to reach anything to push against) in the middle of a large space station module came up:

Hi Commander Hadfield! I’m curious to know, is it possible for someone to get stuck floating in the middle of a room in the ISS? As in they’re floating and the walls are out of reach.

Thanks!

[–]ColChrisHadfield[S] 3512 points 1 year ago

Yes, it is - you can get stuck floating in the center of Node 1, where open space is biggest due to hatches on all sides. But ISS has fans and forced air to mix and refresh the internal atmosphere, so there’s always a small crosswind. Wait long enough, you’ll get pulled to an air inlet.

... and that response led to this excellent question:

I wonder if farting would push you far enough to get unstuck

[–]ColChrisHadfield[S] 3844 points 1 year ago

We all tried it - too muffled, not the right type of propulsive nozzle :)

So, right there, we have some confirmation of what we all expected: astronauts have been trying to fart themselves around space stations. And, from Hadfield’s response, with little luck, though his answer gives us some big clues as to how the fart-propulsion system could be made better.

The reasons he cites for the fart-propulsion not working, “muffled” and “not the right type of propulsive nozzle” both seem like problems that can be solved with some basic equipment.

For “muffled,” the issue is that clothing is in the way, trapping and diffusing the ejected ass-propellant. To solve this, an astronaut could either go pantsless, or, more practically, on-station uniforms would include underwear and pants with a small, velcro-closable access port to allow for unfettered exposure of the anus.

And, speaking of anuses, we should address the next issue, the fact that a human rectum is not the right type of propulsive nozzle for effective reaction-propulsion. He’s right. To get a better idea, here’s a cut-away diagram of a human anus:

As you can see, the anal passage itself is a short tube, encased between the (normally) matching pair of buttocks. There’s a number of problems here. Most obviously, the buttocks themselves cause major exhaust-impingement issues, preventing a free and open flow of the flatus out the anus, and also helping to give farts their trademark, crowd-pleasing sounds.

The anal canal itself is the other big issue, simply being the wrong shape to most effectively turn the gases of flatus into a propellant. To compare, here’s what a simple, basic rocket engine nozzle looks like:

So, you as you can see, the anus is just not up to this task. We’d need some sort of nozzle that compresses and accelerates the gases into a nozzle’s ‘throat,’ then rapidly expands out into the traditional rocket engine bell shape, letting the gas expand, which should increase the linear velocity.

Or so I thought. Like almost everything, rocket nozzle design is something I’m lavishly ignorant of, and so decided to contact an expert, Adrian Sitler. Adrian designs jet engines for Rolls-Royce, so he’s someone who’d really know how to make a fart move you.

The key here is to realize that, barring some nightmarish intestinal issue, most people’s farts are decidedly subsonic in speed. That means the typical bell-housing shape of a rocket nozzle isn’t going to work, and a reaction-engine design specifically for subsonic propellant thrust is needed. Luckily, that exists, and it’s known as a converging nozzle. F-18s use them! Here’s how Adrian explained it:

So the converging nozzle is the correct choice for this low Mach low flow application. However for it to be better than just a pipe, we need to make an assumption. If we can assume constant flow through the nozzle, which would require the user to exert more pressure to overcome the nozzle pressure ratio. In that case the converging nozzle increases thrust. Velocity through a nozzle (assuming lossless) is a ratio of the areas. So AV_inlet = AV_exit making V_exit = AV_inlet/A_exit. If mass flow is conserved then your momentum term (mV) increases with the increased velocity.

Okay, so it looks like the fart-providers will need to try to provide as steady a flow of flatus for the duration of their ‘burn,’ which I’m going to say is an achievable goal. Essentially, what a converging nozzle will do is to constrict the expelled flatus gases to a smaller diameter leading to the outlet, which should increase linear velocity, and should provide more momentum transfer.

Or, more simply, this type of nozzle should ‘shape’ the expelled fart to push against you more effectively to move.

Now, the diameter of the exhaust hole can be a big deal; too big, and you lose the advantages of the converging design, too small and you risk causing back pressure that ruins everything and would probably feel really weird. Testing is needed too determine the optimal diameter.

So, the solution here should be pretty clear. All astronauts working inside space stations with large, enclosed volumes should wear clothing with easy anal access and carry with them a small device like this:

I call it the Anal Propulsion Enhancement via Funnel Actuated Rocketry Tool (APE-FART), and what it essentially is is a simple converging rocket engine nozzle that you can shove up your assHere’s how you use it:

Let’s say you’re an ISS astronaut stranded, floating in the middle of Node 1. Instead of panicking or bothering your busy crew to give you a shove, you simply reach in your pocket and remove your APE-FART.

You then open the Velcro closures on your pants and underwear, giving direct anal access. You then gently but firmly slide the silicone-covered anal-interface tube up your ass, making sure you’re forming as air-tight a seal as possible.

Then, position the exhaust nozzle opposite from the direction you want to travel, and vent out all your farts into the nozzle assembly. According to NASA’s own Bioastronautics Data Book, people can emit up to 2800 ml of flatus a day; that should mean an average astronaut should be able to come up with enough propellant to move themselves to the nearest wall or handhold, which really should be just a few feet away.

Now, the flexible tube can be manipulated to provide some thrust vectoring if needed, but I suspect there will be an efficiency loss if you’re asking the flatus to make a turn in that tube. I suspect a straight run will provide best results, but we really need testing to learn how much would be affected.

Until we can perform this experiment in space, it’s not clear exactly how much thrust or how fast the fart-rocket can propel you. It’s clear that fart-power wouldn’t be especially high-energy, though a hypothetical situation involving severe, liquidy diarrhea probably would eject enough mass with enough force to get a likely very unhappy astronaut going at a good clip.

But the cleanup. It’d be awful.

Outside of a spacecraft, the ejected methane is probably better used as a fuel rather than as the actual reaction gas, a conclusion reached in this Reddit threadas well. By combusting the methane in the flatus, you can get a reaction that produces phenomenally more thrust than with just fart-power alone.

With this in mind, future spacesuit maneuvering units should include some sort of rectal catheter and a pressurized methane containment system to give a bit of extra emergency fuel. In every movie I’ve seen that uses MMUs, someone eventually dies because they run out of fuel. Supplemental fart-fuel may just be the thing to prevent these sorts of tragedies in real life.

So, I think the answer here is that there is real potential for the development of tools to improve the propulsive effectiveness of astronaut farts, and these options should be explored by NASA as soon as possible.

They already have a 3D printer on the station; how hard would it be to print up a couple of APE-FARTS and give it a try? There’s lots to be learned here, and if NASA wants, I’m happy to provide my 3D files to get them started.

Ball’s in your court, NASA.