SoylentNews is people
SoylentNews
Submitted via IRC for SoyCow4463
Artificial gravity breaks free from science fiction
Artificial gravity has long been the stuff of science fiction. Picture the wheel-shaped ships from films like 2001: A Space Odyssey and The Martian, imaginary craft that generate their own gravity by spinning around in space.
Now, a team from CU Boulder is working to make those out-there technologies a reality.
The researchers, led by aerospace engineer Torin Clark, can't mimic those Hollywood creations—yet. But they are imagining new ways to design revolving systems that might fit within a room of future space stations and even moon bases. Astronauts could crawl into these rooms for just a few hours a day to get their daily doses of gravity. Think spa treatments, but for the effects of weightlessness.
[...]"Astronauts experience bone loss, muscle loss, cardiovascular deconditioning and more in space. Today, there are a series of piecemeal countermeasures to overcome these issues," said Clark, an assistant professor in the Ann and H.J. Smead Department of Aerospace Engineering Sciences. "But artificial gravity is great because it can overcome all of them at once."
[...] In a series of recent studies, [they] set out to investigate whether queasiness is really the price of admission for artificial gravity. In other words, could astronauts train their bodies to tolerate the strain that comes from being spun around in circles like hamsters in a wheel?
The team began by recruiting a group of volunteers and tested them on the centrifuge across 10 sessions.
But unlike most earlier studies, the CU Boulder researchers took things slow. They first spun their subjects at just one rotation per minute, and only increased the speed once each recruit was no longer experiencing the cross-coupled illusion.
[...]The personalized approach worked. By the end of 10th session, the study subjects were all spinning comfortably, without feeling any illusion, at an average speed of about 17 rotations per minute. That's much faster than any previous research had been able to achieve. The group reported its results in June in the Journal of Vestibular Research.
Clark says that the study makes a strong case that artificial gravity could be a realistic option for the future of space travel.
"As far as we can tell, essentially anyone can adapt to this stimulus," he said.
(Score: 2) by JoeMerchant on Monday July 08 2019, @12:24AM (13 children)
I've made dynamic spinning systems with unequal length arms - smooth as silk - you'll just need to establish the center of spin at the center of mass, or in the case of the system I made, put (the right amount) more mass on the shorter arm.
Just to go for the semantically obvious: rigid wouldn't be as flexible... a cable, rope, chain type tether can be small, lightweight, easily stowed, quite strong. First you will have to tension the cable, but once that tension is established, rotation about the center of mass comes naturally - all that's left then is to not fight that.
It makes for an interesting / frustrating architecture problem since half the ship will be basically inaccessible to the other half, but these guys in their study worked up slowly to 17 RPM before hitting nausea limits - what's the radius required for 17RPM to generate 1G? I'm feeling lazy, but pretty sure it's gonna have to be bigger than a Gravitron.
🌻🌻 [google.com]
(Score: 2) by maxwell demon on Monday July 08 2019, @06:58AM (5 children)
g = w^2 r
g ~ 10 m/s^2
w = 2*pi*17/60 s^-1 ~ 1.7^2
r = g/w^2 ~ 3 m
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by maxwell demon on Monday July 08 2019, @06:59AM (4 children)
Oops, the 1.7^2 should have been 1.7/s^2.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by maxwell demon on Monday July 08 2019, @07:00AM (3 children)
Err, I should drink some coffee … of course it must be /s (without the ^2).
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by JoeMerchant on Monday July 08 2019, @11:45AM (2 children)
This is why I don't do math for random strangers on the internet, particularly when the board doesn't allow editing...
So, I'm interpreting your gibberish to mean a radius of ~3m would give ~1g for 17rpm - that is pretty impressive, 17rpm at 3m radius is about 4 miles per hour, roughly a fast walk around a 20' diameter circle - hardly seems like that should generate a full g of outward centrifugal "force."
🌻🌻 [google.com]
(Score: 2) by TheSage on Monday July 08 2019, @01:08PM (1 child)
A radius of 3m at 17 rpm gives 3 * 2 * pi * 17 meter per minute which is roughly 20 km/h - the speed of a reasonably fast bicycle.
(Score: 2) by JoeMerchant on Monday July 08 2019, @01:20PM
And, right you are... close to 12mph. I suppose I somehow dropped the 3 when I was calculating 3 * 6.28... 4mph certainly didn't seem fast enough to generate 1g, but I can see 12mph in a tight circle needing 45 degrees of lean on a bike.
🌻🌻 [google.com]
(Score: 0) by Anonymous Coward on Monday July 08 2019, @07:25AM (1 child)
The following gives 3 metres for 17rpm: https://www.artificial-gravity.com/sw/SpinCalc/ [artificial-gravity.com]
At a radius of 250-300m you can spin at a more leisurely 2 to 1.7 rpm. Note: the "cabin" will then be traveling at about 150-200kph. Existing space propulsion tech should still be able to recover a detached cabin that's flying off at 200kph.
There are many bridges with cables about 300m long if not much longer and holding up loads that are much higher than what would be required for at least the first few tests.
You could have "elevators" to travel between the ends. Presumably with counterweights to help balance stuff. You could use a separate counterweight to balance out the differences between the passengers/loads and the main elevator counterweight.
It would be a more useful tech to develop and spend resources on than wasting time and resources going to Mars.
If we ever become a space faring species figuring out the minimum G required for humans and our favorite livestock to stay healthy will be something that will remain important for many generations.
And figuring out those numbers before spending billions or even trillions to settle on Mars might be wiser, especially if it turns out that Mars G just isn't enough. It's a lot harder to increase the G on Mars than "in space".
(Score: 2) by JoeMerchant on Monday July 08 2019, @11:51AM
You certainly could, have virtually anything that's ever been dreamed up on the big screen or in most novels.
The first such ship (which hasn't even been seriously proposed, much less built) should probably stick to something simple and proof of concept, like the current lightsail.
🌻🌻 [google.com]
(Score: 2) by Runaway1956 on Monday July 08 2019, @01:46PM (4 children)
This is one of those "derp" moments. I got to thinking about ropes, cables, and chains, then went on to "anchor chain". That led into a series of thoughts, and I ended back at a somewhat spherical spinning object with a chain holding the two halves together.
So, it doesn't matter much whether the two parts are near equal mass, and your cable can be as flexible as you like. Start the spin going, get it up to the speed you want, then nudge the halves apart. Centrifugal force will drag the chain or cable out. The two bodies will revolve around each other, finding their own equilibrium. When it's time to stop the spin, winch them back together, THEN stop the spin.
I was putting unnecessary complexity into the whole thing. There was no stipulation that the halves be separated before we induced the spin.
(Score: 2) by Immerman on Monday July 08 2019, @03:46PM (3 children)
Let me be the one to poke holes this time: angular momentum is conserved, so as you play out the cable your rate of spin slows, and alternately, reeling in the cable causes your rate of spin to increase. Just as when an ice skater pulls in their arms to go from a slow spin into a fast tight one, and then extend them again to slow down so they can recover gracefully.
For something like a pendulum, where most of the mass is at a point far from the center of rotation, the moment of inertia (rotational analog to inertial mass) is given by I=m*r^2, while angular momentum is L*w (where w=angular frequency in radians per second). So halving the length of the cable causes you to spin 4x as fast in order to maintain constant angular momentum. That's going to get nauseating...
Also, centripetal acceleration = w^2*r, so if you started at 1g acceleration, then halved the cable length, that would increase by a factor of 2^2*1/2 = 2, to 2g. Assuming you've got a lot of halvings to go before you're fully reeled in that';s not going to just nauseate you, it's going to liquefy you.
Fortunately, slowing down the spin isn't actually that hard - just use ion drives or similar for a long slow deceleration with plenty of time to correct for any instabilities. It's only when completely stopped that instabilities become a major problem
(Score: 2) by deimtee on Monday July 08 2019, @05:06PM (2 children)
Runaway's idea could work if you kept a flywheel module at the hub to temporarily 'bank' your angular momentum. Might save some fuel on the spin-up/spin-down cycles if you anticipate having to reel the halves in and out a lot for some reason.
If you cough while drinking cheap red wine it really cleans out your sinuses.
(Score: 2) by Immerman on Monday July 08 2019, @11:30PM (1 child)
My argument was mainly against his "reel them in, *then* slow them down" - that's a recipe for liquefication. If you do both at the same time it's not a problem, but you're back to having to balance the dynamic instabilities which I don't think is actually a problem except as you approach zero rotation. So perhaps it would be a good final stage of the maneuver. (or alternately, one space ship lets go while the other reels in the cable)
I don't think a central flywheel would work well though - you're trying to transmit torque crosswise down a cable. It's going to want to wind the cable around the hub rather than change the speed of the ships on the ends. Which might have some really interesting potential, but I wouldn't want to be the one to test it.
(Score: 2) by deimtee on Tuesday July 09 2019, @04:17AM
You could do it with a small rigid section in the middle. Depending on how fast you want to reel them in, it could be fairly short. You just need to move the line of the cable off the line to the centre of mass.
TBH I think it is unlikely really. You can almost always make use of some delta V to get where you are going faster, and arranging the direction of thrust to both accelerate your ship and to either spin up or spin down is pretty trivial really. I mean, it's rocket science, but it's not difficult rocket science.
If you cough while drinking cheap red wine it really cleans out your sinuses.