I've been wondering if it would be possible to simulate gravity utilizing nothing but large fans constantly blowing air downwards? This is obviously not an ideal setup for a gravity generator, but is it possible? If not, what issues would arise?
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5$\begingroup$ The sensiblist way to make artificial gravity is to have the habitat rotate like in Space Odyssey. This is identical to real gravity from the astronauts' perspective. Plus there is no energy cost once you get it spinning. $\endgroup$– DaronCommented Nov 8, 2022 at 10:28
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7$\begingroup$ Blowing downwards. What, so, like, is the crew wearing some sort of reverse-parachute apparatus to catch the downward draft and pin their feet to the floor? I think the noise and constant wind would drive everyone nuts! $\endgroup$– BMFCommented Nov 8, 2022 at 16:16
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12$\begingroup$ That's one heck of a way to enforce a "clean desk" policy. $\endgroup$– computercarguyCommented Nov 8, 2022 at 17:38
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3$\begingroup$ @Daron "identical to real gravity"...somewhat true...but there are some potentially unsettling side effects to this system, depending on the diameter of the rotating chamber. Turning your head in one direction can cause a disorientating force in a perpendicular direction, which (it is my understanding) can play havoc with sense of balance. Still better than wind, though. $\endgroup$– BeskaCommented Nov 8, 2022 at 21:03
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1$\begingroup$ (tangential:) On the ISS, since there is no downward force to make things fall into a traditional floor drain, fans are how bits of airborne junk find their way into the air filters. Dust and little liquid droplets etc. that would otherwise just hang out in the air are circulated along with the air by the fans and slowly, thanks to the net effect of the air currents, ultimately make their way to the filters--kind of like how floaty bits get filtered out in a swimming pool. (PS it's less than 100% effective: ISS visitors report airborne debris is dense enough to taste and gets in your eyes) $\endgroup$– WyckCommented Nov 9, 2022 at 3:14
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7 Answers
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Something similar is already done in indoor skydiving, though in the opposite direction
A recreational wind tunnel enables human beings to experience the sensation of flight without planes or parachutes, through the force of wind being generated vertically. Air moves upwards at approximately 195 km/h (120 mph or 55 m/s), the terminal velocity of a falling human body belly-downwards.
I hope you agree with me that a wind exceeding 195 km/h (If you want to stand it has to be faster than that) to get a feeling of your own weight it's rather uncomfortable, to put it mildly:
- you would need to wear protective goggles all the time
- loose clothing would become a slapping no no
- turbulence behind anything standing in the flow, including your limbs, would become an hassle
- communication would be almost impossible without proper equipment, the roaring noise would become annoying pretty soon
- eating, drinking, handling anything not sturdy enough would turn into a perennial slapstick comedy
- etc. etc.
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1$\begingroup$ That was my first thought, too. Like, it might work, but the sheer noise of it would be nuts because 1G simulated through air is a lot of air (and then varies based on how you orient yourself). I wonder if it might make an interesting "exercise room", but just spinning the ship/station seems a whole lot easier. Even on the surface of an asteroid you can do those spinny amusement park things if you need gravity somewhere... $\endgroup$– JamieBCommented Nov 8, 2022 at 15:30
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3$\begingroup$ And, for 1G-equivalent wind while standing, you'd better be careful to remain very upright. Tipping over a little will cause a quick and unfortunate increasing effect and SLAM. $\endgroup$– BeskaCommented Nov 8, 2022 at 21:05
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$\begingroup$ In general, it would also allow for people to "redirect gravity" using particular aerodynamic shapes, which makes for a very different experience. $\endgroup$– FlaterCommented Nov 9, 2022 at 0:33
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1$\begingroup$ The accelerometer in your phone would be unaware of the effects of the fan and would still report Earth's acceleration due to gravity (~9.8 m/s² downward) $\endgroup$– WyckCommented Nov 9, 2022 at 2:52
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Simulate gravity for what purpose?
If you have a space station or a space ship, and things floating in the middle of the cabin are a problem for you (for atmosphere control, cleaning, working, etc.), then having a permanent fan or suction system might help a little. Certainly air circulation would be a problem without fans.
But that wouldn't be gravity. The health problems of zero-G would still persist. Directing a fan at the soup bowl would not help to keep the food on the table. As soon as something or somebody blocks the air current, the effect would cease.
So on balance, velcro slippers are a much better idea, or if the structure is large enough, spin gravity.
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8$\begingroup$ Oh, good point! Another liability is that none of your food will stay hot. :-) $\endgroup$– JBHCommented Nov 8, 2022 at 5:56
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3$\begingroup$ @JBH and if rather than floor hoover nozzles that are blocked by the table you rest your soup on you used roof mounted fans then with any substantial downdraft a bowl of soup would not long be a bowl of soup, but just a bowl, getting cold too soon would be the least of your worries there 😁 $\endgroup$– PelinoreCommented Nov 8, 2022 at 10:28
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1$\begingroup$ I think partially blocking the airflow on a bowl of soup would be worse than a complete block. I have this vision of the air forcing the soup out of the bowl from one side and propelling it into the air at fairly high speeds. $\endgroup$ Commented Nov 8, 2022 at 17:41
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$\begingroup$ You'll be glad for the rapid cooling once it starts recirculating in an unending soup shower. $\endgroup$ Commented Nov 8, 2022 at 22:25
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It would not prevent any of the health effects associated with micro-gravity which is the most important reason for artificial gravity. Gravity pulls down on your internal organs and fluids directly. Blowing air does not. This is also the issue with something like magnetic boots, or even shoulder-mounted weights attracted to the floor via magnets: None of them can reach inside your body and act directly on all internal organs and fluids like gravity can.
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Yes... and no...
The problem is that gravity pulls down on every atom (for all intent and purpose) equally. A fan is pushing down only on the skin. From a practical perspective, you're not simulating gravity... you're simulating being at floor level. This means that some muscles (like your heart) will still atrophy.
Does this mean it's a bad idea? Absolutely not! I'm the first to admit I've never heard anyone suggest this solution before. Sometimes being novel is more important than being factual.
Benefits
You're required to circulate air anyway. Might as well be to pushing things down.
Ignoring the liabilities, it does give you something to stand up or push against.
It's adjustable.
Liabilities
There will never be a reason to use a comb.
Wind is chaotic in nature (gravity isn't, in this context). This means that a force great enough to hold you against the floor is also strong enough to push the rest of you to the floor. Standing up straight will be a problem. Walking straight will be a problem. Keeping cargo in one spot without tying it down will be a problem.
And the more mass something has, the more air is needed to keep it on the floor. Little lady weighing a buck-ten requires less air than a big dude weighing a solid two-fifty. The force needed to keep that dude on the floor might send the lady sailing.
Dropping your handkerchief in gravity means it floats gently to the ground near you. Dropping your handkerchief in wind means you probably can't get it back as it'll run around everywhere and finally get sucked into the proverbial cold air return vent.
More seriously, your character might be forced to wear goggles constantly to avoid both impact damage to the eyes and drying the eyes out.
However, +1 for a novel idea. Besides, sometimes oddball ideas work.
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$\begingroup$ If the air flow was laminar, that's a different story! Hi Dustin! $\endgroup$– AronCommented Nov 8, 2022 at 13:59
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3$\begingroup$ @Aron it's no longer laminar when it hits something $\endgroup$ Commented Nov 8, 2022 at 15:04
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1$\begingroup$ re: comb - If you lived in an environment with a constant downward wind force blowing on you, I think the only viable hairstyle would be "buzz cut". Or maybe a bun of some sort. Cornrows maybe. Something very close to the head and controlled. Any even slightly longer loose hair is just going to be blowing around all the time and be a constant distraction. Possibly with enough gel you could keep longer hair under control? $\endgroup$ Commented Nov 9, 2022 at 17:55
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$\begingroup$ There's a formal term for this sort of force: a body force. Centrifugal force (although fictitious) is another example of this. $\endgroup$ Commented Nov 10, 2022 at 20:42
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This won't be mistaken for gravity by anyone:
- Lighter objects and those oriented to block more of the wind will feel more of the force. Gravity doesn't care about orientation or density.
- The "wind tunnel" / "indoor skydiving" analogy only simulates a fall at terminal velocity. You still feel gravity in the usual direction if you place a weighty object on your body blocked by the fan. True antigravity (or a spinning habitat) would remove that weight of that object.
- Fluids (like water or bowls of soup), string, and strips of paper will be batted about by the turbulence from the wind. Gravity won't do such a thing.
- There will be no pressure difference between the blood in your head and feet, as there is when standing against gravity.
- The air blown by the fans has to go somewhere. If you've got inward fans in one place, you'd need outward fans somewhere else - or the air will build up pressure until it's leaking out at the same rate the fans blow it in.
- The wind and effect of the fans would be blocked and redirected by walls, corridors, objects, people, etc. Gravity can't be block or redirected so easily.
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No, because the forces are completely different and everything works differently
I've done a reasonable amount of indoor skydiving, in a vertical wind tunnel. I'm competent at front flying (the traditional skydiving posture), and working on back flying (flying on your back, as the name suggests).
All the techniques of skydiving rely on the fact that the force on any part of your body is dependent on how it faces the wind. On the most basic level, you can radically reduce the force by curling yourself into a ball and fall out of the air, or you can spread your arms and legs wide and get way more force on you. You can walk around, standing vertically, and feel almost no vertical pressure on you, or you can stretch your arms out and take off.
All of this also applies for your concept (in reverse, of course). Essentially your "weight" would become an order of magnitude higher when you're lying down compared to being stood up. I think you'd notice that!
But even before that, you'd notice an even bigger problem. The force you experience isn't simply up and down - the angle of the force depends entirely on the angle of the body surface relative to the air flow. Angle any part of your body at 45 degrees to the air flow, and now the force on that part of your body is 100% sideways. There isn't the slightest possibility that it could resemble gravity under any conditions whatsoever.
And the reason I say "before that" is that these forces are the first thing you're going to notice. Balancing in airflow requires you to be minutely aware of the angles relative to the airflow of all parts of your body. Simply having an elbow or knee extended slightly more on one side than the other will spin you around uncontrollably. You wouldn't even get to the point of noticing the differences in vertical forces, because the first thing you'll experience is sideways forces throwing you around in all sorts of directions.
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1$\begingroup$ This was my first thought. Anything that has sides that aren't perfectly vertical will experience a sideways force, which is very unlike gravity. $\endgroup$– btaCommented Nov 8, 2022 at 22:26
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Gravity pulls on your entire body and your body is designed to push back on the ground through your feet and legs.
Fans would be applying the force to your head and shoulders to force you to the floor. Your average head is not designed to handle that. If your goal is a 1G environment, I can imagine that would be very uncomfortable having all that force on your head and shoulders...worse than wearing a heavy backpack all day. And it would affect everyone differently based on size, and whether you are laying or standing, etc. Maybe a 0.1G environment would work.
The real question is, how would you take a dump in that environment? You would probably still need all the complex equipment that astronauts use today because the wind gravity won't work very well for that. You are going to need some pretty strong toilet suction to counter the vortexes the wind gravity is generating, and I'm not sure I would want my man parts near that.
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1$\begingroup$ How would you take a dump...good call. I didn't think of that $\endgroup$ Commented Nov 8, 2022 at 19:09
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$\begingroup$ You'd need that space suction-toilet either way though. The main point of those is not because your waste won't come out due to lack of gravity, but that it'll come out and just go everywhere... $\endgroup$ Commented Nov 9, 2022 at 17:59
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