Centrifugal gravity for spacecraft: how earthlike?

[River44]

There have been a lot of good, thought provoking topics brought up and putting them all together... Imagine, floating inches off the surface as it is wizzing by you at 90. It'd be great till that wayward chair/desk/computer/trashcan/(insert object here) came along,

I realized after I submitted my post that I should have specified 'a clear area around the entire inner circumference of the the craft', although the mental picture of hitting a console at 90+ does graphically illustrate a more dramatic (or should that be drastic?) example of momentum transfer by something denser than a gas.

or until the 90 mph air resistance caused you to "fall" to the rapidly moving floor to a much more dramatic and possibly comical end...

No air resistance I'm afraid. The interior of the craft would need to be in vacuum in order to stay floating inches from the moving wall. And yes, the second you even lightly brushed the wall, the energy transfer would set you spinning like a top. And if the surface is even slightly abrasive, you would end up with a world class road rash. Not mention any protruding parts (arms, legs, head) being broken from repeatedly slamming against the wall at high speed from the spinning (although I suppose after enough energy has been transferred, it would be considered rolling :lol: ).

 

[kmaduka]

Why not ask that such a experiment be performed at the international space station. Where better to get a real answer. All else is guess work based on missing facts. Remember not so long ago arm chair scientists told us there was no water on the moon, now they say there is water on the moon.

Katibu Maduka
Alliance of Space Explorers and Colonists

 

[MeteorWayne]

Because the ISS doesn't rotate, so there is no "centrifigal gravity" ??

 

[River44]

Why not ask that such a experiment be performed at the international space station. Where better to get a real answer. All else is guess work based on missing facts. Remember not so long ago arm chair scientists told us there was no water on the moon, now they say there is water on the moon.

Two reasons actually. First, if you attempted to spin the ISS to simulate 1g in the crew module, the uneven stresses would cause the entire station to break apart. Second, there is no real comparison with the example you've chosen. There is no relation between a straight forward physics question (how does a ball move under certain conditions) where we know and can mathematically model all the forces involved (spinning object, momentum transfer, vector summing, atmospheric pressure) and a case of exploring an unknown location. While we can make educated guesses about what conditions might be found there, they are still only guesses.

 

[CoreDave]

Because the ISS doesn't rotate, so there is no "centrifigal gravity" ??

I suspect the sugestion was to fly up a new module to the ISS to test the question and practical results. Obviously tying to spin the ISS is just silly but a great big human sized module with its own central hub and spinning section or perhaps for the sake of economy a mouse sized test module. Now I don't know if the ISS has the mass, structural toughness or power needed to run a human sized rotating hab of some kind (I personally favour the module on either end of a rotating stick method). But if it did then it would seem like a worthy endevour, even is we can work out the maths of the motion its hard to predict or understand what the practical impacts on lifeforms would actually be in terms of bone loss reduction, balance issues, etc.

If not as part of the ISS I would like to see some tests flown in the near future. For simplicity and cheapness a module could be connected to a counterweight by a teather and the whole thing spun up. Would be cheaper and easier to engineer that way.

 

[MeteorWayne]

I'll bet this is on the SDC front page

 

[River44]

Because the ISS doesn't rotate, so there is no "centrifigal gravity" ??

I suspect the sugestion was to fly up a new module to the ISS to test the question and practical results. Obviously tying to spin the ISS is just silly but a great big human sized module with its own central hub and spinning section or perhaps for the sake of economy a mouse sized test module. Now I don't know if the ISS has the mass, structural toughness or power needed to run a human sized rotating hab of some kind (I personally favour the module on either end of a rotating stick method). But if it did then it would seem like a worthy endevour, even is we can work out the maths of the motion its hard to predict or understand what the practical impacts on lifeforms would actually be in terms of bone loss reduction, balance issues, etc.

If not as part of the ISS I would like to see some tests flown in the near future. For simplicity and cheapness a module could be connected to a counterweight by a teather and the whole thing spun up. Would be cheaper and easier to engineer that way.

I did not mean to imply that researching the effects of an artificial gravity environment on living organisms was not a worthy research goal, only that we do not need to research how a ball would move under certain controlled conditions because we already know (but it would probably by fun ).

Our rather poor (but improving daily) understanding of how life functions and adapts under changing environmental conditions needs to be rectified and any research that increases our understanding is worthwhile.

 

[elguapoguano]

To create an "artificial" 1G environment via centrifugal force the minimum size is quite a bit less than half a mile (2640 feet) it is actually 735 feet. Which is still large, but a much more manageable size. IMHO this type of approach should be used for manned mars missions, except that you would only need to generate a force equivalent to 3/8th Earth's gravity, so your structure should be considerable smaller than 735 feet.

"The engineering challenges of creating a rotating spacecraft are comparatively modest to any other proposed approach. Theoretical spacecraft designs using artificial gravity have a great number of variants with intrinsic problems and advantages. To reduce Coriolis forces to livable levels, a rate of spin of 2 rpm or less would be needed. To produce 1g, the radius of rotation would have to be 224 m (735 ft) or greater, which would make for a very large spaceship. To reduce mass, the support along the diameter could consist of nothing but a cable connecting two sections of the spaceship, possibly a habitat module and a counterweight consisting of every other part of the spacecraft. It is not yet known if exposure to high gravity for short periods of time is as beneficial to health as continuous exposure to normal gravity. It is also not known how effective low levels of gravity would be to countering the adverse effects on health of weightlessness. Artificial gravity at 0.1g would require a radius of only 22 m (74 ft). Likewise, at a radius of 10 m, about 10 rpm would be required to produce Earth gravity (at the hips; gravity would be 11% higher at the feet), or 14 rpm to produce 2g. If brief exposure to high gravity can negate the health effects of weightlessness, then a small centrifuge could be used as an exercise area."
http://en.wikipedia.org/wiki/Artificial_gravity

 

[Crossover_Maniac]

Concerning the ball in the center of the rotating space station. Assuming it's a cylindrical space station, the air inside of the station will transfer angular momentum to the ball should it be nudged away from the space station axis. This is the principle behind fluid coupling. It's how automatic transmissions work. Transmission fluid transfers torque from the engine to the transmission. There isn't anything solid connecting the two parts, but because fluid is viscous, the transmission still has torque from the engine applied to it. 1-mile diameter space station spending 1 revolution per minute in order to produce earth-like gravity would be rotating at around 200 mph. If someone was to fire a bullet from the axis of such a station to an object at the bottom, it would be subject to very high cross winds depending on the height of the boundary layer. People on the 'ground' (interior wall) of the station won't have to worry about that because they're rotating at 200 mph along with the station. It's assumed they are coupled to the rotating station by the elevator they used to travel from the axis to the 'ground' after boarding the station at an airlock on the axis.

 

[AutoPsychotic]

This is not correct. If the ball is in the center of the ship and you nudge it towards the edge of the ship it will travel in a straight line towards side of the ship (I am neglecting any rotational velocity that the air may impart).

I'm not sure how you can neglect the effect of the air. The air will be spinning with the entire craft (unless the craft was just caused to start spinning) and the ball will likewise approach the same rate of rotation. to an outside observer, the ball will move outward in a spiral.

To the original question, the ball starts in the hand of a person standing on the wall ("floor") of the spinning craft, therefor the ball is spinning at the same rate as the craft. It will fall to the "floor". As someone else mentioned, it won't fall straight down because of the Coriolis effect.

It just occurred to me that the Coriolis effect probably also means that the the occupant will lean somewhat in the spin-ward direction, and walking in that direction would feel like going uphill. If I'm right, the ball will roll around the ring forever in the direction opposite the craft's spin. This "virtual slope" could be countered by making the floor actually slope in the opposite direction. Anyone have any thoughts on this?

You, sir, are correct...although it would be impossible to make the "floor" of the outer circular structure slope as you describe to counter this effect. You would have to "slope" it in sections, or segments, much like how an iris door operates. The resulting effect would be as though the entire floor were made of stairs, going "upstairs" in the direction of rotation and "downstairs" away from the direction of rotation. Think of M.C.Escher's infinite staircase, but in a circle rather than a square.

 

[SpaceTas]

The ball released problem.
------------------------------
Now you need to stay in either the rotating frame of reference or one outside the station (rest frame).
Inside the station the ball in your hand also feels the apparent centrifugal force as the hand that is holding it. It would exert this force on the hand. Remove the hand "under" it, the apparent force is still acting because the ball has the same rotation as it had when held. It would accelerate (as seen inside the station) straight toward the floor. The ball will "feel" less "in station = centrifugal" force when closer to the rotation axis (higher of floor) and so it's apparent acceleration will increase toward the floor. On earth the same thing happens, but because the difference in height is so small compared to the radius, the force of gravity is effectively constant. How "constant" the apparent force is depends upon the size of the station.

The Coriolis effect won't come into play because there is no sideways compared to rotating station. But playing any ball game would have all sorts of curve balls. Spaceball anyone

From outside the station the ball would move off tangental to its previous circular motion in a straight line with constant speed ie constant velocity. Of course the person that dropped the ball will be pushed into a circular path by the wall.

 

[SpaceTas]

ISS and centrifuges
-----------------------
There was plans to build a large variable "gravity" centrifuge on the station, but it was one of the pieces cut at the same time as the Crew Rescue Vehicle, the HAB module. It was actually buit by Japan. Probably no room for the drop ball experiment as it is only 2.5 m in diameter
http://www.spaceref.com/iss/elements/cam.html
http://en.wikipedia.org/wiki/Centrifuge_Accommodations_Module
About the Kibo module
http://kibo.jaxa.jp/en/about/

 

[SpaceTas]

There is another way to get artificial gravity.
Accelerate your space-ship at 1g.

If you can accelerate at 1 g long enough you can get to zoom by anywhere in the Universe within the lifetime of the crew.

Big IF but cool consequences.

 

[AdmiralQuality]

I think the problem here is you're imagining an impractically small ship being rotated for gravity. If you're thinking ISS sized hollow cans, where maybe it's only say, 2 or 3 human height's in diameter, just spinning the can isn't going to be a good solution for gravity. At that scale your feet would be experiencing a lot more G's than your head, and I think you'd just get sick when you added your own movement to it.

So you need a much larger craft (or say, 2 counterbalanced pods out on the end of a big rotating boom). And once you have that, that ball in your hand is rotating the same as you. As soon as you let go, it wants to continue on in a straight line (relative to the ball) but that straight line looks like it's DOWN to you, because you're curving up past it.

And yes, the air around you is also travelling in that same circle. So it's not like the ball "blows away" to the side when you let go of it. The air is following you, around. So to you, there's no wind and the ball seems to fall straight down as usual. But again, this only works at practical, larger scales. If you can reach up into the center of spin just by extending your arm then the scale is too small to be practical. But yes, any object placed exactly in the center of spin is going to be happy to just float there. (Assuming no wind blows it out of center.)

 

[kmaduka]

Why not ask that such a experiment be performed at the international space station. Where better to get a real answer. All else is guess work based on missing facts. Remember not so long ago arm chair scientists told us there was no water on the moon, now they say there is water on the moon.

Katibu Maduka
Alliance of Space Explorers and Colonists

To clarify: I am not suggesting using the international space station as part of the experiment. I’m suggesting that a experiment be performed on or near the station. [/b]

 

[RETerry]

Centrifugal artificial gravity offers an acceleration toward the "outer" containing wall (your simulated floor) equal to the product of the radius and the square of the angular frequency, viz. R•\omega^2. For example one can have Mars gravity (0.37 g) at a rotation rate of 1 rpm with a radius of 331 m. At 2 rpm this radius drops by a factor of 4.

If you jump high enough off your "floor" or "drop" something from a ways overhead, then the apparent gravity gets lower as the radius of the object decreases in the "up" direction. In the Mars example above, with your height at 2 m or less the radial variation of "gravity" is minimal.

"Drop" something in a tube from some distance off the "floor" and it will appear to accelerate toward the ground at a steady rate. Hold a mass on a spring scale and that mass will appear to weigh just what it would on Mars. Gravitational and inertial mass are exactly equal.

Climb a radial ladder toward the center and you must do work against the apparent gravity, "slide" down that ladder and the apparent gravity will do work on you - bruising your butt when it hits the floor.

However if you move along at constant radius, either with or against the rotation direction, then no work is done. There will be no difference in effort walking or trotting in either direction along your "floor" relative to the rotation.

Life becomes more complex and interesting however if you start to pick up any speed and enter the world of Coriolis forces that appear to depend on the velocity of an object. It is here that the "fictitious" nature of these forces in the accelerated frame of reference shows up.

For example higher radial velocity of free fall will appear to force a lateral motion, so that stuff will not "free fall straight" when not sliding along a radial path. If will be impossible to throw a ball to an opposing "floor" without seeing a apparent force curve the trajectory.

But so long as your radial excursions are small compared to the centrifuge's radius and so long as your speeds are small compared to the tangential (or lateral) speed, the truly odd manifestations of your accelerated frame of reference will not be important.

It would be natural to expect that the physiological effects of centrifugal gravity will closely mimic the behaviors in normal gravity, but this has yet to be demonstrated.

 

[icdcow1]

inertia
centrifugal force
velocity
momentum

River44

In agreement with 'A cylindrical craft is launched and begins an interplanetary voyage. If there is a clear area on the inner circumference of the craft, a suited astronaut (before the craft has started rotating) could evacuate the atmosphere, place himself at a stationary point inches from the wall in this area and then have the craft begin rotating. The astronaut would simply remain floating inches from the spinning wall.' by River44.

One should not confuse centrifugal force with gravity. Gravity is inverse to anything one could possibly develop on even the largest of spacecraft. remember E=mc2?

Without mass, there is no gravity.

Gravity is the result of that warp in space/time fabric.

Therefore, there is no such thing as simulated gravity. You either have it or you don't.

The roller coaster is the best analogy of mistaking centrifugal force for gravity.

Were the earth a roller coaster, we would all be flung off into space due to velocity, momentum, and centrifugal force.

Without mass, there is no gravity! Not even simulated gravity.

I will venture to predict, that a law unbeknownst to mankind should be shortly discovered which allows men to simulate mass at various G-Levels. Most likely developed from dark matter/energy research and development, and the innovations which will follow thereafter.

If mass is detached from a gravitational force, it becomes its own gravitational force, no matter how miniscule. Therein lies the problem?

Would go further in depth, but my dog won't crap in his own yard, and needs the gravitational effects of the ultimate digestive solution: 1 G !

 

[MeteorWayne]

kmaduka

Again, what part of the fact that there is no module that can be constructed to conduct the experiment you suggest during the life of the station do you not understand? I'm beginning to suspect you are a spammer...

 

[berberry]

I realized after I submitted my post that I should have specified 'a clear area around the entire inner circumference of the the craft'...

I had thought of saying more about the spacecraft module I had in mind, but it didn't seem essential to my basic question. However, you've brought me to a rather tangential question: suppose there was a need for astronauts to be able to access the artificial gravity chamber (for lack of a better phrase, sorry), while spinning, from other non-spinning parts of the craft. Might one possible solution be a ladder-shaped or web-shaped device ? It would rotate on a track near the access point to the rest of the ship. The track would run along the module's "floor". While astronauts are in the spin room, the web is locked on its track so that it spins with the module. If an astronaut needs to leave, she or he climbs onto the web, releases the lock and the web, perhaps with artificial power (would that be necessary?) gradually assumes equilibrium with the non-spinning spacecraft. The astronaut becomes weightless and easily reaches the module's access point.

Wouldn't that work?

To those who've already mentioned using ladders, wouldn't they require some sort of track, or would it be better to manipulate them via some sort of bar that extends down the module's axis of rotation?

I'm not a scientist, only a curious layman, but I realize that a small chamber spinning at something like 90mph would create incredible motion sickness for humans. I was ignoring this problem, but as I understand it only a fraction of that - only a fraction of 1g, really - would be necessary in order to provide muscle and bone health benefits to astronauts, and thus the ball experiment could take place in a less extreme environment. I see that several posters have pointed that out.

 

[kmaduka]

MeTeorWayne wrote: Again, what part of the fact that there is no module that can be constructed to conduct the experiment you suggest during the life of the station do you not understand? I'm beginning to suspect you are a spammer...
To MeteorWayne
Many people who place comments at Space.com seem to think that NASA and the United States own the “International” Space Station. NASA do not own the International Space Station, the US do not own it. The other nation involved are not so keen on throwing away there investment in it by de-orbiting. Remember Russia and the other partners tend to hold on to a thing until it no longer useful. Let us hope that space exploration and eventually space colonization continue to move forward. I only hope we can pick up the pace.

Katibu Maduka
Alliance of Space Explorers and Colonists

 

[MeteorWayne]

That's pretty funny actually, since I have suspicions you are a spammer, and since I'm a Mod, that could be important

 

[SpaceTas]

A clarification of a previous post. A centrifuge for doing variable gravity experiments was actually built by JAXA (Japan) to be put on ISS station in 2006. It was never added, to save costs. So somewhere in a NASA store (my guess would be MSFC or KSC) there is already a centrifuge module. You might be able to do the drop ball experiment in that! It would have to be small scale done without the human. But could be done if that centrifuge had been delivered.

 

[dj13]

I have thought for a long time that on longer journeys, the simplest solution is to corkscrew thru the distances. Major argument against this is that a straight line is fastest/shortest, but a small ion engine properly oriented could probably negate this and with a slow twist provide all the gravity a crew would need.

 

[torinobradley]

Okay, this is how I understand it. Please correct me if I am wrong.

The spinning disk or ring would have to be of sufficient size to create the necessary simulated gravity which is actually acceleration caused by centrifugal force of an object in constant contact with that surface of the ring. Any object not in contact with that surface would stay on its current trajectory until acted upon by another force, be it air or other physical interaction. If a person on the spinning surface were to drop the "ball" it would only appear to accelerate to the spinning surface because of the now finite trajectory of the ball with only air friction to modify its trajectory and the rings surface being in a constant curve. Of course, the speed at which all this takes place is relative to the size and speed of all factors involved. Now, wouldn't the ball, dependant on mass and air friction, appear to curve away from the actual ring point it was dropped in the opposite direction of the spin? Ahh. Just looked up Coriolis effect. Thats it!

As for how to get off the gravity ride, I kind of picture a module or some sort of little box that you get in and it either slows to match the non-spinning ring so that you may get out on the "non-gravity" part of the craft, or in reverse, would accelerate to match the spinning disk. Now which direction would require acceleration would depend on which part of the craft (body or ring) the module is attached to. Of course, with parallel running rails, each attached to different portions of the craft, all it would need is a set of brakes on each rail.

Very interesting topic!!!

 

[origin]

Okay, this is how I understand it. Please correct me if I am wrong.

The spinning disk or ring would have to be of sufficient size to create the necessary simulated gravity which is actually acceleration caused by centrifugal force of an object in constant contact with that surface of the ring. Any object not in contact with that surface would stay on its current trajectory until acted upon by another force, be it air or other physical interaction. If a person on the spinning surface were to drop the "ball" it would only appear to accelerate to the spinning surface because of the now finite trajectory of the ball with only air friction to modify its trajectory and the rings surface being in a constant curve. Of course, the speed at which all this takes place is relative to the size and speed of all factors involved. Now, wouldn't the ball, dependant on mass and air friction, appear to curve away from the actual ring point it was dropped in the opposite direction of the spin? Ahh. Just looked up Coriolis effect. Thats it!

There is actually no acceleration because it is not a real force, a centrifugal 'force' is a pseudo force. The coriolis effect has nothing to do with the centrifigual force in this case. In the second or third post in this thread I describe how centrifugal force works, I don't want to rewrite it. A ball dropped would not fall directly straight down because it (and your hands that are holding it) are moving at a different velocity than the floor. If the cylinder was very large you would not notice it and if the cylinder was very small it would have a large affect. The apparent nonlinear movement of the ball is not from the coriolis effect.

To leave the rotating chamber it would be a simple matter of climbing a ladder, or walking up a ramp the center of the cylinder. As you approached the center of the cylinder your weight would decrease until you were weightless at the center. The reason your weight would decrease is because as you approached the center of the cylinder your velocity would decrease (remember your velocity is dictated by the rigidly mounted ramp or ladder). The access would be at the center of rotation of the cylinder at an end.