I wonder if anyone can tell me why artificial gravity seems to be out of fashion. In "2001" we saw Arthur C Clarke's idea of a rotating space station in the form of a massive wheel....but that (1968) was a long time ago.
Now we only hear about almost insurmountable feats of human endurance with astronauts having to undergo strenuous excercise routines and still lose massive amounts of muscle mass on a projected trip to Mars.
Surely you only need to tether two small spaceships, or capsules together and make them spin about a mutual centre of mass to create artificial gravity. Better still would be a lightweight rigid pylon connecting the two. The whole thing could be set spinning when it is finally in free-fall on its journey, or in orbit as appropriate.
I just cannot understand what the problem is.
It's simply not practical. We haven't even found the graviton yet, so any attempt to create gravity boards (for instence) seems very futuristic, for the moement anyhow.
When you visit asteroid artificial gravity may hold us up.Should revive.Visiting asteroid is must in our future ,if we like to survive.
For a rotating space station to be viable, it would have to be very big. This is because in order to have little to no difference in gravity between your head and your feet, the size of a room (ie 8ft high) would have to be little compared to the radius of the rotating circle. Given the enormous cost in getting just a small object into space, the cost of putting a space station large enough to practically impliment centrifugal gravity is astronomical and far beyond NASA's budget (though I'm sure they'd consider it if they could afford it).
At present the issues with long term microgravity are not enough to be too bad. If any sudden health problem does occur, Earth is nearby and at present astronauts on the Shuttle suffer no effects and those from the ISS are only a little weaker for a while when they return.
Tethering two crafts together and setting them rotating would be possible but the technical issues and the danger if the tether snaps probably isn't worth it.
A manned mission to Mars would need to consider artifical gravity though. Perhaps not for the entire ship but a small compartment which could be made to spin fast enough to allow an astronaut to do an hour or two gym work out in normal gravity each day, thus making them work a bit harder and putting a bit of 'normal' stress on their bones. Mars has weaker gravity than Earth but add the weight of a space suit and you'd probably way more than you did at home (obviously sans the space suit).
At present the issues with long term microgravity are not enough to be too bad. If any sudden health problem does occur, Earth is nearby and at present astronauts on the Shuttle suffer no effects and those from the ISS are only a little weaker for a while when they return.
Tethering two crafts together and setting them rotating would be possible but the technical issues and the danger if the tether snaps probably isn't worth it.
A manned mission to Mars would need to consider artifical gravity though. Perhaps not for the entire ship but a small compartment which could be made to spin fast enough to allow an astronaut to do an hour or two gym work out in normal gravity each day, thus making them work a bit harder and putting a bit of 'normal' stress on their bones. Mars has weaker gravity than Earth but add the weight of a space suit and you'd probably way more than you did at home (obviously sans the space suit).
Alpha Numeric,
Thanks for a sensible reply. However, I know from past experience, when I ask the question "why has something not been done" there is never any shortage of invalid answers to defend the status quo. Perhaps there is an adequate answer but yours is not it.
As I implied in my question, you don't need to build a massive wheel! You only need to tether two objects together and make them rotate about their mutual centre of mass, like a binary star.
As for minimum size, let's say the capsules were 100ft apart. if you were standing up, the acceleration at the top of your head would be more than 7/8 of that at your feet. Would that be a problem? I very much doubt that it would be as much of a problem as being weightless.
Thanks for a sensible reply. However, I know from past experience, when I ask the question "why has something not been done" there is never any shortage of invalid answers to defend the status quo. Perhaps there is an adequate answer but yours is not it.
As I implied in my question, you don't need to build a massive wheel! You only need to tether two objects together and make them rotate about their mutual centre of mass, like a binary star.
As for minimum size, let's say the capsules were 100ft apart. if you were standing up, the acceleration at the top of your head would be more than 7/8 of that at your feet. Would that be a problem? I very much doubt that it would be as much of a problem as being weightless.
I agree torchy.
Regarding the danger of the tether snapping: have 2 or more redundant tethers! So, not a problem.
There are other problems that make this impractical. For an Earth-orbiting space station, you have the problem of docking with the habitable module, which becomes nearly impossible unless you have a full-blown "pinwheel" station ala Clarke's proposal -- which IS prohibitively expensive at this point, but perhaps achievable and practical once the price per pound to orbit drops below $100...
For a trip to Mars, you want a ship with ultra-high specific impulse engine. Right now, that means a low-thrust engine that continuously accelerates for half the journey, and then decelerates for the other half (e.g. plasma rockets, or ion engines, etc.) This would drastically shorten the trip time, and reduce astronaut exposure to space radiation as well as various other space hazards (like micro-meteoroids...) Yet such continuous-acceleration mission designs aren't compatible with tethered modules (or else, each module will have to have its own engine and fuel supply, and the firing of the two sets of engines would have to be meticulously coordinated.... and of course the MTBF of such a system would be half of what it'd be otherwise...)
There are other problems that make this impractical. For an Earth-orbiting space station, you have the problem of docking with the habitable module, which becomes nearly impossible unless you have a full-blown "pinwheel" station ala Clarke's proposal -- which IS prohibitively expensive at this point, but perhaps achievable and practical once the price per pound to orbit drops below $100...
For a trip to Mars, you want a ship with ultra-high specific impulse engine. Right now, that means a low-thrust engine that continuously accelerates for half the journey, and then decelerates for the other half (e.g. plasma rockets, or ion engines, etc.) This would drastically shorten the trip time, and reduce astronaut exposure to space radiation as well as various other space hazards (like micro-meteoroids...) Yet such continuous-acceleration mission designs aren't compatible with tethered modules (or else, each module will have to have its own engine and fuel supply, and the firing of the two sets of engines would have to be meticulously coordinated.... and of course the MTBF of such a system would be half of what it'd be otherwise...)
No, obviously it would not be used in conjunction with continuous linear aceleration (of the order of g), it would be used instead of it. I am not familiar with whatever plans there are for manned flights to Mars, but if it was done conventionally, using relatively short burns of fuel and most of the journey in free fall then presumably it would not be much of a problem.
I was thinking of a light weight triangulated pylon rather than a tether, because I assume a small space vehicle on a tether would be a bit like a bus hung from a crane. You couldn't move around inside without making it swing all over the place. Then it starts to be a bit silly to worry about a substantial piece of properly designed structure breaking (any more than thousands of other things that could go wrong if they were not properly designed).
Of course, it could even be a 25 to 30m long tube, making the two modules effectively one. The whole thing would still not be excessively big. Rotation speed = approximately 7.7 rpm.
I think that the continuous linear acceleration that you envisage would be a small fraction of g and pobably nowhere near enough to prevent the long term effects of (near) weightlessness. Therefore artificial gravity should be used in conjunction with small continuous linear acceleration (unless I am missing something).
Presumably you would want the linear motion to be in the direction of the axis of rotation. Then, if the (linear) acceleration was very small, the ion drive (or whatever) could be positioned at the centre of gravity. Surely it could be done, it's not rocket science.
On the question of an orbiting space station, if it was of the form described above, you would have two choices for docking: either you would temporarily stop the rotation of the space station (without very much expenditure of fuel), or more likely make the docking spaceship rotate to synchronise (even less fuel).
It's not hard to work out that you don't need a massive wheel.
I was thinking of a light weight triangulated pylon rather than a tether, because I assume a small space vehicle on a tether would be a bit like a bus hung from a crane. You couldn't move around inside without making it swing all over the place. Then it starts to be a bit silly to worry about a substantial piece of properly designed structure breaking (any more than thousands of other things that could go wrong if they were not properly designed).
Of course, it could even be a 25 to 30m long tube, making the two modules effectively one. The whole thing would still not be excessively big. Rotation speed = approximately 7.7 rpm.
I think that the continuous linear acceleration that you envisage would be a small fraction of g and pobably nowhere near enough to prevent the long term effects of (near) weightlessness. Therefore artificial gravity should be used in conjunction with small continuous linear acceleration (unless I am missing something).
Presumably you would want the linear motion to be in the direction of the axis of rotation. Then, if the (linear) acceleration was very small, the ion drive (or whatever) could be positioned at the centre of gravity. Surely it could be done, it's not rocket science.
On the question of an orbiting space station, if it was of the form described above, you would have two choices for docking: either you would temporarily stop the rotation of the space station (without very much expenditure of fuel), or more likely make the docking spaceship rotate to synchronise (even less fuel).
It's not hard to work out that you don't need a massive wheel.
QUOTE (torchy+Sep 1 2007, 01:38 PM)
As I implied in my question, you don't need to build a massive wheel! You only need to tether two objects together and make them rotate about their mutual centre of mass, like a binary star.
AN talked about tethering 2 spacecraft together in his post. You have accused him on not reading you're whole post, bit in actuality, it's the other way around.
And I agree, it would be technically unfeasible to try to get 2 spacecraft orbiting around an arbitrary point. One would most certainly go faster or slower than the other, and drag the first off center. You will have one ship whipping around the other like a flail. It sounds like a catastrophe waiting to happen.
EDIT: and even if you did get them perfectly balanced with each other, how would you plan on docking with one of the ships?
AN talked about tethering 2 spacecraft together in his post. You have accused him on not reading you're whole post, bit in actuality, it's the other way around.
And I agree, it would be technically unfeasible to try to get 2 spacecraft orbiting around an arbitrary point. One would most certainly go faster or slower than the other, and drag the first off center. You will have one ship whipping around the other like a flail. It sounds like a catastrophe waiting to happen.
EDIT: and even if you did get them perfectly balanced with each other, how would you plan on docking with one of the ships?
Latrosicarius,
OK I didn't read AN's reply completely, however you obviously didn't read it properly either. He did not say, or imply "it would be technically unfeasible to try to get 2 spacecraft orbiting around an arbitrary point".
You have clearly not realised the fact that any object in space or in free fall, when caused to rotate, will do so about its centre of mass. This would apply even if the whole object consisted of two parts connected by a tether. There would be no question of any "instability" or one object "whipping around the other".
This can easily be demonstrated by throwing two connected balls into the air, connected by a string (like Agentinian boleadoras). Using balls of different weights does not prevent a stable state from being reached quite rapidly.
As can be seen above, I have developed the idea during this debate to a design in which two "modules" (of approximately the same weight) would be connected by a hollow shaft. When you mention docking you have not read my posts properly, since I have already covered that.
Developing it a bit further, a visiting spaceship would dock at the centre of rotation, synchronising its own rotation to that of the space station (quite slow). I appreciate that this (c of g) may not coincide with the docking hatch, so I have a simple solution to that problem. a pair of rails would be provided either side of the docking hatch, extending a few metres. The spaceship would be equipped with short wheeled grabs that would attach to the rails. It would then be able to slowly track its self over the hatch. During that tracking process, the overall centre of mass, and hence centre of rotation of the whole object would change very slightly. The angular velocity would also change, but that change would be extremely small.
Regarding stresses, remember that the maximum centripetal acceleration of the modules is g. Hence the tensile stress in the shaft would be the same as if one module was hanging on the shaft on earth. Tension is easier to resist than compression, and think of towers that resist compression and wind loading on earth. I suggest that the stresses that have to be resisted by a typical airliner fusalage (in extreme design conditions) are worse and less predictable than in the rotating space station.
OK I didn't read AN's reply completely, however you obviously didn't read it properly either. He did not say, or imply "it would be technically unfeasible to try to get 2 spacecraft orbiting around an arbitrary point".
You have clearly not realised the fact that any object in space or in free fall, when caused to rotate, will do so about its centre of mass. This would apply even if the whole object consisted of two parts connected by a tether. There would be no question of any "instability" or one object "whipping around the other".
This can easily be demonstrated by throwing two connected balls into the air, connected by a string (like Agentinian boleadoras). Using balls of different weights does not prevent a stable state from being reached quite rapidly.
As can be seen above, I have developed the idea during this debate to a design in which two "modules" (of approximately the same weight) would be connected by a hollow shaft. When you mention docking you have not read my posts properly, since I have already covered that.
Developing it a bit further, a visiting spaceship would dock at the centre of rotation, synchronising its own rotation to that of the space station (quite slow). I appreciate that this (c of g) may not coincide with the docking hatch, so I have a simple solution to that problem. a pair of rails would be provided either side of the docking hatch, extending a few metres. The spaceship would be equipped with short wheeled grabs that would attach to the rails. It would then be able to slowly track its self over the hatch. During that tracking process, the overall centre of mass, and hence centre of rotation of the whole object would change very slightly. The angular velocity would also change, but that change would be extremely small.
Regarding stresses, remember that the maximum centripetal acceleration of the modules is g. Hence the tensile stress in the shaft would be the same as if one module was hanging on the shaft on earth. Tension is easier to resist than compression, and think of towers that resist compression and wind loading on earth. I suggest that the stresses that have to be resisted by a typical airliner fusalage (in extreme design conditions) are worse and less predictable than in the rotating space station.
I read somewhere that the act of moving within a rotating object can cause nausea, particularly moving up and down. This could cause problems when the transport ship docks at the center and the crew have to climb or use a lift to get to the rotating sections. I suppose, the larger the diameter, the less this nausea affect will have.
Granted, astronauts are trained to be resistant to motion sickness.
Granted, astronauts are trained to be resistant to motion sickness.
QUOTE (torchy+)
OK I didn't read AN's reply completely, however you obviously didn't read it properly either. He did not say, or imply "it would be technically unfeasible to try to get 2 spacecraft orbiting around an arbitrary point".
No offense, but I think you need to improve your reading comprehension skills. Observe:
No offense, but I think you need to improve your reading comprehension skills. Observe:
QUOTE (AlphaNumeric+)
Tethering two crafts together and setting them rotating would be possible but the technical issues and the danger if the tether snaps probably isn't worth it.
QUOTE (torchy+)
You have clearly not realised the fact that any object in space or in free fall, when caused to rotate, will do so about its centre of mass. This would apply even if the whole object consisted of two parts connected by a tether. There would be no question of any "instability" or one object "whipping around the other".
Here is the key term. "when caused to rotate." I understand that an external component can spin objects around easily, but only because that component is fixed, anchored, or standing firm and is largely unaffected by the objects it's spinning. But when each object is responsible for applying the correct amount of thrust to itself at exactly the same time, and countering any pivoting, yawing, or rolling in real-time, I'm sure you can see how this would be doable in theory, but very difficult in practice.
Here is the key term. "when caused to rotate." I understand that an external component can spin objects around easily, but only because that component is fixed, anchored, or standing firm and is largely unaffected by the objects it's spinning. But when each object is responsible for applying the correct amount of thrust to itself at exactly the same time, and countering any pivoting, yawing, or rolling in real-time, I'm sure you can see how this would be doable in theory, but very difficult in practice.
Latro,
I'm glad you understand how washing machines work... or at least you can see them working so you can't deny it. The question is how do rotating bodies in space work. In spite of your attitude I will answer your points seriously, mainly for the benefit of other readers.
There are two issues:
1. A rigid dumbell shaped body as I advocate, consisting of two approximately equal modules connected by a shaft, and a docking hatch near the centre. Being rigid, it can only rotate about one axis and translate in one direction. (the six motions sum to two resultants). In an age when inherently unstable fighter planes can be made to fly perfectly smoothly, I fail to see what the problem would be in getting it to rotate and translate about exactly the required axes. In fact I am quite sure it could have been achieved with late sixties technology.
2. The question of two modules rotating about each other linked only by a tether is academic, since I dismissed it for the reasons above. However, I fail to see the problems that you seem to envisage about disasters being caused by lack of perfect synchrinisation or differences in weights - because they don't exist.
"You will have one ship whipping around the other like a flail".
I think not. Once the tether was taut and no further forces applied, any erratic movements would contravene Newton's laws of motion.
In reply to N O M, yes I can see that the coriolis forces caused by standing up and sitting down could cause nausea, but I would have thought it would not be as bad as being in a ship in rough sea since the problem would go away as soon as you stopped. Better put up electronically corrected (falsified) external images instead of windows though.
Incidentally, jumping would be interesting. When you left the floor, it would continue in a circular arc whereas your c of g would move along a chord. The result would be that (if you jumped vertically (radially)) you would land slightly forward of where you took off.
I'm glad you understand how washing machines work... or at least you can see them working so you can't deny it. The question is how do rotating bodies in space work. In spite of your attitude I will answer your points seriously, mainly for the benefit of other readers.
There are two issues:
1. A rigid dumbell shaped body as I advocate, consisting of two approximately equal modules connected by a shaft, and a docking hatch near the centre. Being rigid, it can only rotate about one axis and translate in one direction. (the six motions sum to two resultants). In an age when inherently unstable fighter planes can be made to fly perfectly smoothly, I fail to see what the problem would be in getting it to rotate and translate about exactly the required axes. In fact I am quite sure it could have been achieved with late sixties technology.
2. The question of two modules rotating about each other linked only by a tether is academic, since I dismissed it for the reasons above. However, I fail to see the problems that you seem to envisage about disasters being caused by lack of perfect synchrinisation or differences in weights - because they don't exist.
"You will have one ship whipping around the other like a flail".
I think not. Once the tether was taut and no further forces applied, any erratic movements would contravene Newton's laws of motion.
In reply to N O M, yes I can see that the coriolis forces caused by standing up and sitting down could cause nausea, but I would have thought it would not be as bad as being in a ship in rough sea since the problem would go away as soon as you stopped. Better put up electronically corrected (falsified) external images instead of windows though.
Incidentally, jumping would be interesting. When you left the floor, it would continue in a circular arc whereas your c of g would move along a chord. The result would be that (if you jumped vertically (radially)) you would land slightly forward of where you took off.
QUOTE (torchy+)
In spite of your attitude I will answer your points seriously, mainly for the benefit of other readers.
I wasn't aware I was giving you attitude problems. Maybe you thought that because I disagreed with you, that I was writing in a nasty inflection? I assure you this is not the case.
QUOTE (torchy+)
The question of two modules rotating about each other linked only by a tether is academic, since I dismissed it for the reasons above.
I have been referring to a tethered system this entire time. I assumed a large rigid structure would be too large to carry into orbit. If you are talking about a rigid structure now, then it is (of course) much easier to do.
QUOTE (torchy+)
However, I fail to see the problems that you seem to envisage about disasters being caused by lack of perfect synchrinisation or differences in weights - because they don't exist.
"You will have one ship whipping around the other like a flail".
I think not. Once the tether was taut and no further forces applied, any erratic movements would contravene Newton's laws of motion.
"You will have one ship whipping around the other like a flail".
I think not. Once the tether was taut and no further forces applied, any erratic movements would contravene Newton's laws of motion.
This phrase was an exaggeration. I realize, that with 2 ships of the same mass, one will not stay stationary and flail the other around. They will both be moving, but if one of them becomes off-pitch slightly, it's thrust could be misdirected and provide an undesirable net thrust in one direction or the other for the entire tethered system. Both ships would have to have very precise computer-controlled station-keeping abilities. Not only must their orientation to one-another, remain perfectly fixed but during the spin-up period, they must each exert equal thrust in an opposite tangential vector in respect to the virtual centerpoint.
In addition, in order to prevent orbital decay and maintain a safe and steady height above the Earth, each station must periodically exert upward or downward thrust simultaneously, which will be exacerbated in difficulty due to the fact that their positions are continuously varying in respect to the Earth as they orbit the centerpoint.
Suffice it to say, it will be hard using a tethered system. Perhaps unfeasible considering the difficulty and risk involved. What happens if one of the RCS thrusters becomes damaged? How will it be repaired? It will be unable to slow and stop its spinning without going out of alignment. Neither can a shuttle dock with a spinning station, unless the station has an unmoving centerpoint, which the shuttle can slid up next to and match its spin.
In addition, in order to prevent orbital decay and maintain a safe and steady height above the Earth, each station must periodically exert upward or downward thrust simultaneously, which will be exacerbated in difficulty due to the fact that their positions are continuously varying in respect to the Earth as they orbit the centerpoint.
Suffice it to say, it will be hard using a tethered system. Perhaps unfeasible considering the difficulty and risk involved. What happens if one of the RCS thrusters becomes damaged? How will it be repaired? It will be unable to slow and stop its spinning without going out of alignment. Neither can a shuttle dock with a spinning station, unless the station has an unmoving centerpoint, which the shuttle can slid up next to and match its spin.
I said, you said, he said, she said ---- bah!
The obvious point is that idiots at NASA, despite years of training, years of space travel and keen imaginative minds that solve highly complex problems on a regular basis don't have the imagination to implement artificial gravity at the ISS. I think this is a really sad state of affairs, and should be rectified immediately.
</sarcasm>
I thought AlphaNumeric answered the question very well.
I'm no expert, but here are my top 10:
1. no-gravity negative effects are minimal
2. Costs to implement and maintain are high
3. Risks/dangers are high
4. docking is an issue
5. Space walk complexities, don't drop your wrench
6. Solar panel orientation becoms a dynamic issue
7. Light/dark due to rotation would drive you crazy
8. Thermal stresses would become more dynamic and extreme
9. Competition for the no-gravity hub room for sex
10. Most importantly, would ruin the view.
Oh, I forgot --- Would ruin all the low gravity experiments they are there to perform.
I wonder if the differential gravity (head to foot differences) caused by a 100ft diameter wheel would have ill effects. How about the way things would fall. Processing for lot of that stuff is built into our neural systems.
The obvious point is that idiots at NASA, despite years of training, years of space travel and keen imaginative minds that solve highly complex problems on a regular basis don't have the imagination to implement artificial gravity at the ISS. I think this is a really sad state of affairs, and should be rectified immediately.
</sarcasm>
I thought AlphaNumeric answered the question very well.
I'm no expert, but here are my top 10:
1. no-gravity negative effects are minimal
2. Costs to implement and maintain are high
3. Risks/dangers are high
4. docking is an issue
5. Space walk complexities, don't drop your wrench
6. Solar panel orientation becoms a dynamic issue
7. Light/dark due to rotation would drive you crazy
8. Thermal stresses would become more dynamic and extreme
9. Competition for the no-gravity hub room for sex
10. Most importantly, would ruin the view.
Oh, I forgot --- Would ruin all the low gravity experiments they are there to perform.
I wonder if the differential gravity (head to foot differences) caused by a 100ft diameter wheel would have ill effects. How about the way things would fall. Processing for lot of that stuff is built into our neural systems.
meBigGuy,
My original question was not why are NASA and other space scientists so stupid but what is it that I have missed that makes the idea such a bad one. Yes, and is it such a bad one.
On your last point: absolutely, I am sure that a large part of the point of current and recent space stations has been to study, and do experiments in zero gravity. But isn't it funny that the Russians in particular have spent a large amount of their time in space stations studying the harmful effects of weightlessness on humans and how to combat them.
That brings me to your point number 1. You've got to be kidding! Have you seen the Russian cosmonauts (why don't we call tham astronauts?) arriving back on Earth from Mir, apparently being kept reclining in seats until they get enough strength to stand. If the negative effects were minimal, there wouldn't be so much research into them.
Correct me if I am wrong, but I think that the currently expected time for a manned mission to reach Mars is more than the record endurance of weightlessness.
Now 2-10:
2. I am not convinced that the extra percentage costs on a very expensive undertaking would be prohibitive.
3. Risks/dangers - a bit too general but again, men to Mars already an incredibly dangerous undertaking. Real dangers are in details.
4. Docking - dealt with above.
5. Space walk complications. I suggest use of robot arms, but if necessary stop the spin and restart. The energy put into the spin would be extremely small compared with that for forward motion.
6. Solar panel orientation - not at all insurmountable. e.g. point the axis of spin generally towards the Sun, and solar panels face it.
7. Dealt with. Why would you want windows on a journey to Mars?
8. Thermal stresses. Less overall temperature changes than without spinning, and changes too slow for fatigue.
9. Point taken!
10. See 7.
Just returning to the nausea question - you know they call the plane used to cause weightlessness the vomit comet.
It is interesting what you say about how things would fall, also jumping etc. I think that most of the effects would be quite small and we learn to adjust for these things. e.g. there were some famous experiments demonstrating that on people who constantly wore goggles that would reverse their vision horizontally or vertically.
My original question was not why are NASA and other space scientists so stupid but what is it that I have missed that makes the idea such a bad one. Yes, and is it such a bad one.
On your last point: absolutely, I am sure that a large part of the point of current and recent space stations has been to study, and do experiments in zero gravity. But isn't it funny that the Russians in particular have spent a large amount of their time in space stations studying the harmful effects of weightlessness on humans and how to combat them.
That brings me to your point number 1. You've got to be kidding! Have you seen the Russian cosmonauts (why don't we call tham astronauts?) arriving back on Earth from Mir, apparently being kept reclining in seats until they get enough strength to stand. If the negative effects were minimal, there wouldn't be so much research into them.
Correct me if I am wrong, but I think that the currently expected time for a manned mission to reach Mars is more than the record endurance of weightlessness.
Now 2-10:
2. I am not convinced that the extra percentage costs on a very expensive undertaking would be prohibitive.
3. Risks/dangers - a bit too general but again, men to Mars already an incredibly dangerous undertaking. Real dangers are in details.
4. Docking - dealt with above.
5. Space walk complications. I suggest use of robot arms, but if necessary stop the spin and restart. The energy put into the spin would be extremely small compared with that for forward motion.
6. Solar panel orientation - not at all insurmountable. e.g. point the axis of spin generally towards the Sun, and solar panels face it.
7. Dealt with. Why would you want windows on a journey to Mars?
8. Thermal stresses. Less overall temperature changes than without spinning, and changes too slow for fatigue.
9. Point taken!
10. See 7.
Just returning to the nausea question - you know they call the plane used to cause weightlessness the vomit comet.
It is interesting what you say about how things would fall, also jumping etc. I think that most of the effects would be quite small and we learn to adjust for these things. e.g. there were some famous experiments demonstrating that on people who constantly wore goggles that would reverse their vision horizontally or vertically.
I was making no comment with regard to a trip to Mars, just in context of ISS. So, consider it a misunderstanding. News to me it's "out of fashion".
Well I only got that impression because I've seen quite a lot of different television programmes and articles mentioning the problems of prolonged weightlessness, only talking about how to withstand it, not to try to remove the problem.
QUOTE (torchy+Sep 20 2007, 07:39 PM)
meBigGuy,
My original question was not why are NASA and other space scientists so stupid but what is it that I have missed that makes the idea such a bad one. Yes, and is it such a bad one.
On your last point: absolutely, I am sure that a large part of the point of current and recent space stations has been to study, and do experiments in zero gravity. But isn't it funny that the Russians in particular have spent a large amount of their time in space stations studying the harmful effects of weightlessness on humans and how to combat them.
That brings me to your point number 1. You've got to be kidding! Have you seen the Russian cosmonauts (why don't we call tham astronauts?) arriving back on Earth from Mir, apparently being kept reclining in seats until they get enough strength to stand. If the negative effects were minimal, there wouldn't be so much research into them.
Correct me if I am wrong, but I think that the currently expected time for a manned mission to reach Mars is more than the record endurance of weightlessness.
Now 2-10:
2. I am not convinced that the extra percentage costs on a very expensive undertaking would be prohibitive.
3. Risks/dangers - a bit too general but again, men to Mars already an incredibly dangerous undertaking. Real dangers are in details.
4. Docking - dealt with above.
5. Space walk complications. I suggest use of robot arms, but if necessary stop the spin and restart. The energy put into the spin would be extremely small compared with that for forward motion.
6. Solar panel orientation - not at all insurmountable. e.g. point the axis of spin generally towards the Sun, and solar panels face it.
7. Dealt with. Why would you want windows on a journey to Mars?
8. Thermal stresses. Less overall temperature changes than without spinning, and changes too slow for fatigue.
9. Point taken!
10. See 7.
Just returning to the nausea question - you know they call the plane used to cause weightlessness the vomit comet.
It is interesting what you say about how things would fall, also jumping etc. I think that most of the effects would be quite small and we learn to adjust for these things. e.g. there were some famous experiments demonstrating that on people who constantly wore goggles that would reverse their vision horizontally or vertically.
Torchy,
I read somewhere many years ago that the limiting factor for a rotating space station was the disorientation that astronauts would feel with fast rotation. IIRC, the minimum rate was about 1-2 rotation per minute. I believe the work was done by... by... Garard O'Neil (http://en.wikipedia.org/wiki/Gerard_K._O'Neill) he wrote several books on space stations in the late seventies and early eighties.
One design had modules on ether end of a tether with a central module as well that did not rotate and an inflated flexible tube around the teather that the astronauts could use to move from one module to another.
Also if you allowed for a central module that did not rotate, you could very easily apply thrust from this point without a great deal of computation. I believe he also used water storage to ballence the modules. much like planes move fuel from tank to tank to maintain their weight distribution.
Also, A Russian spent a little more then one year in space (IIRC), A trip to Mars with current technology takes about 6 months to get there with a year stay and another 6 months to return.
You not only loose muscle mass but bone mass as well! This is the larger long term problem!
TEOTW(AWKI)
My original question was not why are NASA and other space scientists so stupid but what is it that I have missed that makes the idea such a bad one. Yes, and is it such a bad one.
On your last point: absolutely, I am sure that a large part of the point of current and recent space stations has been to study, and do experiments in zero gravity. But isn't it funny that the Russians in particular have spent a large amount of their time in space stations studying the harmful effects of weightlessness on humans and how to combat them.
That brings me to your point number 1. You've got to be kidding! Have you seen the Russian cosmonauts (why don't we call tham astronauts?) arriving back on Earth from Mir, apparently being kept reclining in seats until they get enough strength to stand. If the negative effects were minimal, there wouldn't be so much research into them.
Correct me if I am wrong, but I think that the currently expected time for a manned mission to reach Mars is more than the record endurance of weightlessness.
Now 2-10:
2. I am not convinced that the extra percentage costs on a very expensive undertaking would be prohibitive.
3. Risks/dangers - a bit too general but again, men to Mars already an incredibly dangerous undertaking. Real dangers are in details.
4. Docking - dealt with above.
5. Space walk complications. I suggest use of robot arms, but if necessary stop the spin and restart. The energy put into the spin would be extremely small compared with that for forward motion.
6. Solar panel orientation - not at all insurmountable. e.g. point the axis of spin generally towards the Sun, and solar panels face it.
7. Dealt with. Why would you want windows on a journey to Mars?
8. Thermal stresses. Less overall temperature changes than without spinning, and changes too slow for fatigue.
9. Point taken!
10. See 7.
Just returning to the nausea question - you know they call the plane used to cause weightlessness the vomit comet.
It is interesting what you say about how things would fall, also jumping etc. I think that most of the effects would be quite small and we learn to adjust for these things. e.g. there were some famous experiments demonstrating that on people who constantly wore goggles that would reverse their vision horizontally or vertically.
Torchy,
I read somewhere many years ago that the limiting factor for a rotating space station was the disorientation that astronauts would feel with fast rotation. IIRC, the minimum rate was about 1-2 rotation per minute. I believe the work was done by... by... Garard O'Neil (http://en.wikipedia.org/wiki/Gerard_K._O'Neill) he wrote several books on space stations in the late seventies and early eighties.
One design had modules on ether end of a tether with a central module as well that did not rotate and an inflated flexible tube around the teather that the astronauts could use to move from one module to another.
Also if you allowed for a central module that did not rotate, you could very easily apply thrust from this point without a great deal of computation. I believe he also used water storage to ballence the modules. much like planes move fuel from tank to tank to maintain their weight distribution.
Also, A Russian spent a little more then one year in space (IIRC), A trip to Mars with current technology takes about 6 months to get there with a year stay and another 6 months to return.
You not only loose muscle mass but bone mass as well! This is the larger long term problem!
TEOTW(AWKI)
The End,
Almost.
Thanks for the link to the Wikipedia item on Gerard O'Neill.
I did not see the work on it by him, but I did search for artificial gravity on Wikipedia. It seems that there has been no shortage of thought and work on this subject after all!
Interesting that they actually did an experiment with Gemini and Agena at opposite ends of a tether! Unfortunately rotating too slowly to produce any noticeable effects. Perhaps the purpose was only to do it before the Russians did. Presumably, even if they had gone faster they would not have had problems with Coriolis force, or excessive swinging around because they were confined to their seats.
I see what the (apparent) problems were.
Two tethered capsules are not very practical, as I mentioned before, but if what you they say is right and you need 2rpm or less, then you need 224m radius for 1g. But... notice that the required radius is inversely proportional to the square of the angular velocity, so the reqd. rpm for 30m dia. (14m rad. to hip) would be 8 (not 10 as they stated). i.e. the actual radius of rotation reduces to 1/16.
I wonder what experiments they could possibly have done to adequately simulate Coriolis force, but presumably they did some.
They certainly suggest that it would be possible to get used to higher rpm, and as I said before, if you did not move you wouldn't feel anything.
Almost.
Thanks for the link to the Wikipedia item on Gerard O'Neill.
I did not see the work on it by him, but I did search for artificial gravity on Wikipedia. It seems that there has been no shortage of thought and work on this subject after all!
Interesting that they actually did an experiment with Gemini and Agena at opposite ends of a tether! Unfortunately rotating too slowly to produce any noticeable effects. Perhaps the purpose was only to do it before the Russians did. Presumably, even if they had gone faster they would not have had problems with Coriolis force, or excessive swinging around because they were confined to their seats.
I see what the (apparent) problems were.
Two tethered capsules are not very practical, as I mentioned before, but if what you they say is right and you need 2rpm or less, then you need 224m radius for 1g. But... notice that the required radius is inversely proportional to the square of the angular velocity, so the reqd. rpm for 30m dia. (14m rad. to hip) would be 8 (not 10 as they stated). i.e. the actual radius of rotation reduces to 1/16.
I wonder what experiments they could possibly have done to adequately simulate Coriolis force, but presumably they did some.
They certainly suggest that it would be possible to get used to higher rpm, and as I said before, if you did not move you wouldn't feel anything.
QUOTE (torchy+Sep 14 2007, 08:43 PM)
Incidentally, jumping would be interesting. When you left the floor, it would continue in a circular arc whereas your c of g would move along a chord. The result would be that (if you jumped vertically (radially)) you would land slightly forward of where you took off.
I was just thinking about this problem and I can't decide whether it would be possible to lose the artificial "gravity" effect completely and remain suspended in mid-air just by jumping at a certain angle against the rotation...
I was just thinking about this problem and I can't decide whether it would be possible to lose the artificial "gravity" effect completely and remain suspended in mid-air just by jumping at a certain angle against the rotation...
Yes, if you achieve a state of rest with respect to the irrotational part of the hub, you will be in inertial unaccelerated motion and experience no gravity. You will experience the rest of the toroid zooming past you at speed v=g/R and if there is air friction your freedom (from "gravity") will come to an end.
Actually, I tried to do the math on this and got something of this sort:
- in order for everyone to be able to avoid nausea caused by the Coriolis force, Wiki sez you'd have to spin the cylinder/torus at 2 rpm or lower, which would call for a radius of 224 m if you want to generate 1g
- at this size and rotation frequency, your linear (tangential) speed at any time you lose contact with the surface (by jumping) would be about 46 m/s
- knowing that the average human is able to jump vertically up to about 20 inches in Earth's natural 1g field and assuming this is done by the legs generating constant force for 0.5 seconds, I estimate that the average human weighing 70 kg is capable of accelerating itself (relatively) by about 16 m/s^2
- since it takes the human 9.81 m/s^2 of that just to leave the cylinder's surface "vertically", we can clearly see that the "horizontal" application of the rest of the leg force to produce the rest of the acceleration (~6.2 m/s^2) during a 0.5-second jump would be far from sufficient to nullify the "horizontal" speed of 46 m/s, so the only result would be (depending on the "horizontal" direction of the jump - with or against the rotation) how fast/hard and how far away they would land (but they would still land pretty soon)
The only 1g-cylinder where it would really be possible (even for trained athletes) to jump to a point of mid-air weightlessness is a much smaller cylinder that has to rotate faster to achieve 1g, which would give nausea to most if not all people. I.e. something not likely to be built in the first place (unless someone's willing to screen astronauts for the ability to adapt to frequencies like 3-4-5 rpm before putting them up there; this might be the cost-effective solution, since at 3 rpm you already only need a radius of 99.5 m to achieve 1g).
- in order for everyone to be able to avoid nausea caused by the Coriolis force, Wiki sez you'd have to spin the cylinder/torus at 2 rpm or lower, which would call for a radius of 224 m if you want to generate 1g
- at this size and rotation frequency, your linear (tangential) speed at any time you lose contact with the surface (by jumping) would be about 46 m/s
- knowing that the average human is able to jump vertically up to about 20 inches in Earth's natural 1g field and assuming this is done by the legs generating constant force for 0.5 seconds, I estimate that the average human weighing 70 kg is capable of accelerating itself (relatively) by about 16 m/s^2
- since it takes the human 9.81 m/s^2 of that just to leave the cylinder's surface "vertically", we can clearly see that the "horizontal" application of the rest of the leg force to produce the rest of the acceleration (~6.2 m/s^2) during a 0.5-second jump would be far from sufficient to nullify the "horizontal" speed of 46 m/s, so the only result would be (depending on the "horizontal" direction of the jump - with or against the rotation) how fast/hard and how far away they would land (but they would still land pretty soon)
The only 1g-cylinder where it would really be possible (even for trained athletes) to jump to a point of mid-air weightlessness is a much smaller cylinder that has to rotate faster to achieve 1g, which would give nausea to most if not all people. I.e. something not likely to be built in the first place (unless someone's willing to screen astronauts for the ability to adapt to frequencies like 3-4-5 rpm before putting them up there; this might be the cost-effective solution, since at 3 rpm you already only need a radius of 99.5 m to achieve 1g).
Here's a little question.
Say you have a space station rotating like this pic. If you jumped straight up, would you be able to pass through, without banging into the sides?
User posted image: User posted image
P.S. I just realized this thread is two years old lol
Say you have a space station rotating like this pic. If you jumped straight up, would you be able to pass through, without banging into the sides?
User posted image: User posted image
P.S. I just realized this thread is two years old lol
QUOTE (Latrosicarius+Jun 3 2009, 03:46 PM)
Here's a little question.
Say you have a space station rotating like this pic. If you jumped straight up, would you be able to pass through, without banging into the sides?
User posted image: <a target='_blank' href='http://zhost.tk/up/7f3ae756729ac1d4600961fc2b31ab18.JPG'>User posted image</a>
P.S. I just realized this thread is two years old lol
I would think that coriolis force would result in hitting the sides of the corridor.
Say you have a space station rotating like this pic. If you jumped straight up, would you be able to pass through, without banging into the sides?
User posted image: <a target='_blank' href='http://zhost.tk/up/7f3ae756729ac1d4600961fc2b31ab18.JPG'>User posted image</a>
P.S. I just realized this thread is two years old lol
I would think that coriolis force would result in hitting the sides of the corridor.
QUOTE (Latrosicarius+Jun 3 2009, 08:46 PM)
If you jumped straight up, would you be able to pass through, without banging into the sides?
Straight up, no. You'd definitely bang into the sides because your trajectory would be straight and horizontal, whereas the corridor would spin around the center. Depending on the width of the corridor and the size and speed of the cylinder, you may be lucky enough to fall right past the entry corner and miss it.
But if the situation is such that you can jump past a certain height, your fall trajectory will take you right smack into that wall.
Straight up, no. You'd definitely bang into the sides because your trajectory would be straight and horizontal, whereas the corridor would spin around the center. Depending on the width of the corridor and the size and speed of the cylinder, you may be lucky enough to fall right past the entry corner and miss it.
But if the situation is such that you can jump past a certain height, your fall trajectory will take you right smack into that wall.
Yes, donjo, that is what I was trying to ask. Thanks
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