h a l f b a k e r y
Not the Happy Cuddle Club.
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
or get an account
See the link for some details about "O'Neill cylinders". These
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
If a cylinder in space is 8km in diameter, we multiply by the
constant "pi" to get the circumference, about 25 1/8 km.
by the rotation rate, 40 times per hour, to get
surface speed" of 1005 km/hr. If you were in a spaceship
and near the O'Neil cylinder, but not moving in relation to it,
would see the hull of the rotating cylinder moving by your
Now imagine you are inside that cylinder, on its inner surface,
running AGAINST its rotation ("anti-spinward", it is called). If
could move 1005 km/hr (slower than the speed of sound) you
would cancel out the effects of the rotation of the cylinder and
in Zero-Gee, and could simply float with respect to the axis of
cylinder. Not for very long, though, so long as the cylinder is
filled with a decent amount of air. That's because there would
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
Cylinders in space
As mentioned in the main text. [Vernon, Jul 14 2015]
Arthur C Clarke
Prescient as ever .. [8th of 7, Jul 14 2015]
||Is that multiply by or divide by?
||Wait a minute...what's the idea here? It certainly fits the category.
||Sorry about not thinking about the category when I posted
||[RayfordSteele], it is definitely "multiply" (typo fixed).
||Alternatively, just delete the external universe. Then
your cylinder has nothing to spin relative to, and
you'll have a force-free interior.
||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], 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?
||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.
||Well, there's my something-new for the day.
||This is a pretty fun idea. though not one we could try
soon, as youve got to have the tech infrastructure and
political will to build classic, 8000 m diameter ONeil
cylinders in space.
||The maths 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. Thats 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.
||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.
||[CraigD], did you not see the part about using longer bats
or golf clubs?
||[Vernon], I saw your speculation about using extra-long
clubs, but didnt pursue it, because I think long drive
and longest club golf enthusiasts and competitors have
shown that extra-long clubs dont 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 freakn
space engineers, I imagine they wouldnt 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, youd 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
||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 ONeil
cylinder of only 1333 m diameter would have the same
v=~81 as the 1/6th g full-size, 8000 m one.
||[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.
||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.