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# O'Neill Hovering

If you run fast enough in the correct direction...
 (+3, -1) [vote for, against]

See the link for some details about "O'Neill cylinders". These are proposed to be built in outer space, about 8 kilometers in diameter, rotating 40 times an hour to simulate 1Gee of gravitational force, on the inside of the cylinders.

The key word is "simulate", so let's have a bit of fun with some details....

If a cylinder in space is 8km in diameter, we multiply by the math constant "pi" to get the circumference, about 25 1/8 km. Multiply by the rotation rate, 40 times per hour, to get "interior surface speed" of 1005 km/hr. If you were in a spaceship outside and near the O'Neil cylinder, but not moving in relation to it, you would see the hull of the rotating cylinder moving by your viewport at that speed.

Now imagine you are inside that cylinder, on its inner surface, running AGAINST its rotation ("anti-spinward", it is called). If you could move 1005 km/hr (slower than the speed of sound) you would cancel out the effects of the rotation of the cylinder and be in Zero-Gee, and could simply float with respect to the axis of the cylinder. Not for very long, though, so long as the cylinder is filled with a decent amount of air. That's because there would be a 1005 km/hr headwind that would quickly slow your motion and make you once more contact the inner surface of the cylinder, experiencing simulated gravity.

They probably won't build transport systems that fast inside an O'Neill cylinder. However, that is not what this Idea is about. Consider a baseball or a golf ball, for example. Is it humanly possible to hit it anti-spinward such that it begins to hover in Zero-Gee? Perhaps by using an extra-long baseball bat or golf club? Perhaps we should build an O'Neill cylinder just so we can find out!

 — Vernon, Jul 14 2015

Cylinders in space https://en.wikipedi.../O%27Neill_cylinder
As mentioned in the main text. [Vernon, Jul 14 2015]

Arthur C Clarke https://en.wikipedi...endezvous_with_Rama
Prescient as ever .. [8th of 7, Jul 14 2015]

Is that multiply by or divide by?
 — RayfordSteele, Jul 14 2015

Wait a minute...what's the idea here? It certainly fits the category.
 — normzone, Jul 14 2015

[RayfordSteele], it is definitely "multiply" (typo fixed).
 — Vernon, Jul 14 2015

 Thoroughly discussed.

 — 8th of 7, Jul 14 2015

Alternatively, just delete the external universe. Then your cylinder has nothing to spin relative to, and you'll have a force-free interior.
 — MaxwellBuchanan, Jul 14 2015

What a waste ... you have no idea of the simple pleasure that can be derived from a large basket of tribbles, a 12-gauge shotgun, and a modified tennis ball launcher.
 — 8th of 7, Jul 14 2015

[8th of 7], if the basket is large enough, and stocked with food, then they will reproduce as fast as you remove them from the basket, so all you need to do is keep adding food. Will your "simple pleasure" then eventually become boring enough that you would stop?
 — Vernon, Jul 15 2015

No.
 — 8th of 7, Jul 15 2015

Re. the Arthur C. Clarke link - Rendezvous with Rama was brilliant. But the sequels, co-written with Gentry Lee were absolutely dire. I was astonished that Clarke lent his name to them.
 — MaxwellBuchanan, Jul 15 2015

 Well, there's my something-new for the day.

that was close
 — 2 fries shy of a happy meal, Jul 16 2015

 This is a pretty fun idea. though not one we could try soon, as you’ve got to have the tech infrastructure and political will to build classic, 8000 m diameter O’Neil cylinders in space.

 The math’s a bit wrong in the OP – centripetal acceleration is a = v^2/r, giving for a=9.8 m/s/s and r=4000 m v=~198 m/s. That’s a lot more than any common human-powered thing can throw – the best golf ball drives are ~95 m/s, the fastest bow driven arrows 120 – but if the cylinder is only producing a Moon-like a=1.6 m/s/s, the required speed is only v=~81 m/s, within the realm of golf.

If we imagine spinning a cylinder to 1/6 g while its open to space and air free, a playful engineer with a good swing and a purpose-made (no pitch up on its face) golf club could hit a ball at just the right speed antispinward that it circled the cylinder many times, never changing height above the interior surface. I imagine it might even be a popular, thought rare, sport.
 — CraigD, Jul 16 2015

For long-term habitation, you're going to have to design for 0.6-0.7 g minimum, otherwise muscle atrophy will disable those returning to an earth-normal environment.
 — 8th of 7, Jul 16 2015

[CraigD], did you not see the part about using longer bats or golf clubs?
 — Vernon, Jul 16 2015

 [Vernon], I saw your speculation about using extra-long clubs, but didn’t pursue it, because I think “long drive” and “longest club” golf enthusiasts and competitors have shown that extra-long clubs don’t perform much better, or even as well, as ordinary-length ones. EG: the longest certified golf drive, 471 m in 1974 by pro golfer Mike Austin, used a 1.10 m club, shorter than most present day drivers, while the club holding the Guinness record for length, 6.24 m managed only a 60 m drive.

 Since this idea assumes the folk involved are freak’n space engineers, I imagine they wouldn’t have trouble cobbling together something that could throw a ball well over the needed 198 m/s. Hobbyists on Earth have thrown them from air cannons at 600 m/s

 For low-mass, large-area bodies like golf balls, speed falls fast due to air friction, so for the “hovering” effect to be impressive, you’d need to either have no air, as I imagined, or use a lower-area projectile, such as an arrow. I like the airless approach, because the effect could last a long, long time… perhaps minutes, perhaps days.

 For it to be an athletic sport, though, I think the projectile speed has to be kept in the realm of 100 m/s.

The speed equation is v = sqrt(a r) where a is the centripetal acceleration and r the radius, so rather than reducing a, you could reduce r. A downsized O’Neil cylinder of only 1333 m diameter would have the same v=~81 as the 1/6th g full-size, 8000 m one.
 — CraigD, Jul 17 2015

[CraigD], OK, thank you. I note that if we really wanted 1/6 G, we could simply spin the cylinder more slowly. probably 6 & 2/3 times per hour.
 — Vernon, Jul 17 2015

 Or just have the "Hover driving range" as a shelf part way "up" the end of the cylinder. All you need is a small platform for teeing off and a net behind you for protection from perfect drives.

 You could have one shelf on the outside for zero resistance drives. Make the balls out of something that will evaporate completely to avoid adding to the space junk problem.

On the inside, would it be possible to hit a ball with an upward trajectory such that as it is slowed by air resistance it comes to a stop at the axis of rotation? Of course that is not a stable position, so it would come back down eventually, but there could be competitions to see who can hit a ball that stays "up" the longest. Then you just need to carefully track the balls and deploy drones with nets to catch them before they hit someone.
 — scad mientist, Jul 17 2015

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