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Gravity in space

Posted by: Stefan Sigwarth - Sat Aug 21, 2004 11:30 am
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Gravity in space 
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Post Gravity in space   Posted on: Sat Aug 21, 2004 11:30 am
Hello fellows, i'm new here and i am not a space engineer, so please don't shoot me. :wink:

If space tourisme really wants to lift off, (imo) it can't rely upon just the healthy population of our planet. Off course at first, when sub-orbit is only for those who can afford it, but when space tourism will really boom and it will get below € 10k, you can't sent people to a weightless environment for more then a day. Supposedly you stay at least 3 days in orbit for someone new to space, i'm sure no one can sleep or can use any 'corridors' without crashing into everything and everyone, no doubt causing some damage along the way.

In a sense, its entirely unpractical for the normal man who has not a lot of hours working inside a space station. You must ensure that these tourists will not just float around and bump into everything, or you will need to steer/sent them to another place, for say with a rail where you can attach yourself (the tourist) to it, in order to get another view, to eat or something like that. Obviously, this would look rather hilarious and accidents will easily happen in such manner.

Nor can you give every tourist a crash course in spacetraining, that would certainly crank up the price and the duration of the whole story. So you would probably need to create a earth-like environment where any person, young or old, can walk around as normal as here on earth. With the current technology, that would be nearly impossible but it certainly must be possible to create enough gravity so at least your brains have no trouble disorientating or your internal organs will float around alot, no doubt resulting in a messy place.
But, obviously, the ideal situation would be to have earth gravity, or at least 70-80% feeling of it, i suppose that would be more then acceptable.

But how to achieve this? I heard that on ISS, they use a litle spin to atleast make it easier for the occupients to see whats up and done, or at least, that's how it was explained.

The technique is simple and everyone knows about it. If you have a bucket half-full of water and sweep it around your head, at some point the water won't fall out the bucket if you have it sweeped upside down. The water is pushed/thrown against the bottom of the bucket.
This also works with any objects, but the greater the mass, the greater the speed the 'bucket' must travel in this trajectory i suppose. So if there would be a rather huge circular spacestation spinning around an axe (large enough to not hurt your feet of the curving ground), i wonder how fast it would have to turn so that people in it, could normally walk? I bet this would be either so fast that you woukd get dizzy if there were any windows in this structure.

But are there other forms of creating gravitation in an artificaial way? I'm not talking about making an object as heavy as the earth or any exotic StarTrek (TM) concept, but about what we can achieve with any technology we have today.

I used the search and didn't see (m)any discussion threads about generating gravity in any convential way, so.... ;)


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Post    Posted on: Sat Aug 21, 2004 2:16 pm
In one of the discussions concerning the Space Elevator you will find a little bit.

The only realistic concept of artificial gravity known to me is a rotating wheel in principle. Spoken quite exactly it is simulating gravity but noone will recognize that and the effects on a man's physiology doesnt be nearly indifferent compered to real normal gravity. The concept is based on Einstein's gravity-acceleration-equivalency.

Yuor post sounds like you know all this. If you want it I would be able to explain it a liitle bit.

I myself sometimes think about another effect that seems to cause artificial gravity. If a spacecraft is accelerating there must be automatically gravity simulation at the wall opposite to the direction of acceleration.

The cocept based on rotation is discussed a little bit for use at Mars missions. In this case a cable would connect thart part the astronauts are living in to the engine part. That section of the engine part the astronauts' part is connected to will be rotating. So the astronauts' part will rotate around the engine and the astronauts will have artificial gravity inside the outer wall of their part.

The whole rotation concept in principle is very similar to the idea of space elevators...



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Post    Posted on: Sat Aug 21, 2004 2:44 pm
Ekkehard Augustin wrote:

...

Yuor post sounds like you know all this. If you want it I would be able to explain it a liitle bit.



I know some basics, but i don't know the whole story.
I would appreciate it if you would :)


Ekkehard Augustin wrote:
I myself sometimes think about another effect that seems to cause artificial gravity. If a spacecraft is accelerating there must be automatically gravity simulation at the wall opposite to the direction of acceleration.

The cocept based on rotation is discussed a little bit for use at Mars missions. In this case a cable would connect thart part the astronauts are living in to the engine part. That section of the engine part the astronauts' part is connected to will be rotating. So the astronauts' part will rotate around the engine and the astronauts will have artificial gravity inside the outer wall of their part.

The whole rotation concept in principle is very similar to the idea of space elevators...

Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


I'm not sure if i follow, but how fit this rotation into a space elevator? I read the space.com articles about the elevator, but i don't think i read about this principle. Could you point me to some articles that incorporates this rotation concept into the elevator?


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Post    Posted on: Sat Aug 21, 2004 2:54 pm
Some claim that element 115, a superheavy man-made element, generates a gravitational field that radiates from the nucleus and that this might be used to generate or even counteract gravity.

HOWEVER, even if these claims were tru, it would take a rediculous amount to do anything because of the fact that 115 has a halflife of about 20 milliseconds...

The other possibility would be to tether two of the orbiting crafts to eachother. If you set these tethered crafts in motion, it would generate a sense of gravity. The stationkeeping would be very hard on two tetherd crafts however, and the idea ends up being somewhat impractical.

I believe that the centrifugal force that you can create by rotating a vehicle around its center of mass could be used, but I'm not sure how the motion would be sustained... Also, I'm not sure of the gradient of gravity and how that would affect the people on the craft... The gradient would be much greater on one rotating space ship than on two thethered ships because of the smaller distance to the rotation axis. The gradient, for anyone who doesnt know, is the difference between the gravity at theeye level and the gravity on the floor... On a rotating spacecraft, this gradient might cause some problems with blood circulation and such, but I'm really not sure.

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Post    Posted on: Sat Aug 21, 2004 4:38 pm
The one shift that has made the immediate construction of space colonies a little less interesting is that we realized that most of the stuff that you "have" to do in space needs to be done in zero G and if you want to do button pushing, you might as well do it on earth.

I mean, when I can afford a tourist trip to space (and if I can't before I'm pushing up the dasies, I'm going to be a very pissed off corpse) I'm going to want to spend as much of the time I'm up there in freefall as possible.

For long-long term stuff, you are probably going to need gravity. Apparently, pregnancy in zero gravity is not the world's greatest idea, especially because it's a massive question mark as to the long-term effects. Same as the long term effects of space in general.

Although, you might want to have some sort of rotating frame, say two spheres seperated by a cable, for those folks who are far too spacesick to enjoy the experience.

The big one is that you need a pretty long arm of rotation -- at least a mile or two -- or else it's going to be mighty uncomfortable for the people there.

I have never heard of the theoretical properties of element 115, eraurocktchick87, but when I did some research, it seems to mostly be the realm of the UFO whackos and less in the realm of actual science.


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Post    Posted on: Sat Aug 21, 2004 4:46 pm
siggy wrote:
Ekkehard Augustin wrote:

...

Yuor post sounds like you know all this. If you want it I would be able to explain it a liitle bit.



I know some basics, but i don't know the whole story.
I would appreciate it if you would :)


Okay. Lemme see if I can do the Five-MinuteCrash Course in General Relativity.

Next time you're riding in a car, take a ball along. Doesn't really matter what kind of ball, but small ones are best (think like a superball or a hand-exercise or stress ball). When the driver turns a corner towards the left (especially a sharp one), throw the ball straight up in the air (but don't bounce it off the ceiling -- drivers get mad if you hit them with it). Because the ball is in free-fall (not connected to the car), it continues on its parabolic path that was determined the moment it left your hand.

However, the car is accelerating into a different velocity (aka changing direction). So while the ball is continuing on its free-fall path, the car is turning towards it, so that the ball seems to fall towards the window.

Now, if you actually understood all that without having to do it, here's where it gets hairy.

Imagine that you conducted the same experiment, but this time you were in the back seat of a limousine. Instead of being tinted, the windows have been replaced with solid, opaque plastic, so that you cannot see out. The window leading to the driver is also opaque, so that you cannot tell whether the driver is turning the wheel.

Now, if the driver were to turn in a continual, regular circle, and you were to throw your ball up in the air this time, the ball would always fall slightly sideways. It would appear to you as if the side of the car was exerting a gravitational force on you and the ball.

It is through several thought experiments similar to this one that Einstein proved that acceleration and gravity are indistinguishable.

The number of uses for this in space colonization and development is truly (pardon the pun) astronomical, but the primary use is for orbital and free-floating stations with semi-permanent or permanent crews.

We've already proven that constant acceleration and gravity are indistinguishable from one another, so the trick is to put a constant acceleration on the station. One way is to build the station just like a conventional earth-based skyscraper, put a big engine on the bottom, and regulate the engine so as to give a constant acceleration. Although this creates problems when you want to keep the station in a stable and consistent orbit, it's great for long-haul spaceships (and is how gravity is expected to be replicated on long missions, such as one to Mars or Jupiter).

So now we want to give our station a constant acceleration, but keep it in the same place. So we need some way to constantly be accelerating away from a single point in space, but manage to keep the whole thing in one place. So the central point has to remain static (or else the station moves -- which is a definite Bad Thing), the distance from that point to the outer edge has to remain static (or else the acceleration changes), and the speed of the station has to remain static (again, or else the acceleration changes).

The name for the shape described by a point A moving through a plane and keeping a static distance from point B is a circle.

This leads us to the most efficient form of space station design, the torus: simply build a big metal doughnut in space, and spin it at a constant speed around a central axis (which, since it does not rotate, is where the docking ports are located). This is the traditional form of "artificial gravity", and the best example is the orbital Hilton hotel in Stanley Kubrick's movie 2001: A Space Odyssey, based on Arthur C. Clarke's book by the same name.

eraurocktchick87 wrote:
The other possibility would be to tether two of the orbiting crafts to eachother. If you set these tethered crafts in motion, it would generate a sense of gravity.


Cathleen, here, accidentally hit on the economy version: build two really big soup cans (one as a habitation module, the other as a life-support/farm module), connect them to each other by a long collapsible access tube with an airlock at the center, and spin them at a constant rate. If designed well, such a mini-station could support a small group of people almost indefinitely. Independent honeymoon cottages orbiting Jupiter, anyone? Stationkeeping isn't actually that much harder than with an individual spaceship.

eraurocktchick87 wrote:
I believe that the centrifugal force that you can create by rotating a vehicle around its center of mass could be used, but I'm not sure how the motion would be sustained... Also, I'm not sure of the gradient of gravity and how that would affect the people on the craft... The gradient would be much greater on one rotating space ship than on two thethered ships because of the smaller distance to the rotation axis.


Spinning a single small spaceship, however, is not operable, as the gradient is far too steep (even the two-tin-can model has a radius of a couple hundred meters), and will actually tend to cause some rather nasty tidal effects (meaning the passengers will get ripped apart).

Ekkehard Augustin wrote:
I myself sometimes think about another effect that seems to cause artificial gravity. If a spacecraft is accelerating there must be automatically gravity simulation at the wall opposite to the direction of acceleration.

The cocept based on rotation is discussed a little bit for use at Mars missions. In this case a cable would connect thart part the astronauts are living in to the engine part. That section of the engine part the astronauts' part is connected to will be rotating. So the astronauts' part will rotate around the engine and the astronauts will have artificial gravity inside the outer wall of their part.


Good job, Herr Augustin. A vehicle similar in design to what you suggest can be found in Austin Meyer's Space Combat, a free physics-based spaceship simulator. A picture of the Colony Ship (I'm pretty sure that's the name of it) is at the top of the page. The habitation modules are the large round things connected to the main axis, and the Orion Drive nuclear engine is way back in the background (the little silver round things are the tops of some seriously huge fuel tanks). It's a beautiful example of gossamer spacecraft design.

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Post    Posted on: Sat Aug 21, 2004 4:51 pm
Yeah true, freefall could be nice and would be nice, but its simply unpractical. In any tourism space station will have a part for zero-gravity and a part where you can at least walk and sleep. I doubt old people are 'fit' enough to go around in zero gravity.

Another (rather silly) option would be something like magnetic shoes which stick onto the floor where the magnetic shows will need to do the same as a normal shoe would do. Stick and unstick at several points of the shoe so you actually walk. Though it would be funny to see that you really need to keep your arms down to prevent them from swirling around your body :D Walking like that would probably feel like walking on a small tether high up in the air.

All the technology to do these kind of things are here atm. It's just waiting for that one little break through so that a lot of people will get interest.


spacecowboy wrote:
...


thanx, very understandable and logical :)


Last edited by Stefan Sigwarth on Sat Aug 21, 2004 5:00 pm, edited 1 time in total.



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Post    Posted on: Sat Aug 21, 2004 5:00 pm
just want to point out that this was a course in inertia, not general relativity :P , but explained much better than i could have.

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Post    Posted on: Sat Aug 21, 2004 6:06 pm
siggy wrote:
But are there other forms of creating gravitation in an artificial way? I'm not talking about making an object as heavy as the earth or any exotic StarTrek (TM) concept, but about what we can achieve with any technology we have today.


There has not been any mention of a “credible artificially made gravity” except centrifugal gravity as you have mentioned. Or at least it is still a long way off.

For a ships, a large section can be made and a hamster type wheel can be installed in side it to give the crew artificially gravity for long journeys, and putting a counter rotating section around it would solve the problem of gyroscopic rotationally forces. This section can carry most if not all of the creature comforts for the crew, like sleeping, showers, bath rooms eating and living quarters. On larger structures a pin wheel like structure or a cylinder type structure will be needed as you have mentioned.


siggy wrote:
If space tourism really wants to lift off, (imo) it can't rely upon just the healthy population of our planet. Off course at first, when sub-orbit is only for those who can afford it, but when space tourism will really boom and it will get below € 10k, you can't sent people to a weightless environment for more then a day. Supposedly you stay at least 3 days in orbit for someone new to space, I’m sure no one can sleep or can use any 'corridors' without crashing into everything and everyone, no doubt causing some damage along the way.


There will probably be a short orientation for the trips and some motion sickness pills for thaws who have a problem with the weightless environment. The rest will be a crash course. Pardon the pun. For space tourism logistics an accommodations will probably be the limit factor for tourism. When they get to the € 10k level they should have enough experience to solve most of these problems

siggy wrote:
This also works with any objects, but the greater the mass, the greater the speed the 'bucket' must travel in this trajectory i suppose.


No the large the circle the slower the speed of rotation is needed.


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Post    Posted on: Sat Aug 21, 2004 6:08 pm
IMO, the first tourists will go up in space to experience weightlessness besides the view out the window. later on,whne they will actually live in space for extended periods of time, there will be a demend for artifivial gravity.

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Post    Posted on: Sat Aug 21, 2004 6:57 pm
Science fiction writers have been blathering on and on about zero-g geriatric clinics. Or geriatric clinics on the moon. Really, the fun one is getting the old folks up into space, not when they are actually there. And, in either case, the part that sucks is going back to gravity after a long time. Makes some sense, especially if you have weak bones.

Also, they tried magnetic shoes on Skylab. What they found is that astronauts generally preferred to float, so they haven't tried that since. What you really need is better toe dexterity and a tail. ;)

The best explanation of inertia and reference frames was a 50s era video they showed us in my high school physics class. They had two professorly types doing a variety of amusing demonstrations, including having one of them hanging from the ceiling and the camera upside-down with the other one on the ground and demonstrating a rotating frame by sitting at a table against a wall, all on a rotating bearing, while a grad student pushed them in circles and showing different camera angles.


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Post    Posted on: Sat Aug 21, 2004 8:41 pm
Hello, asiggy,

in principle there is nothing to add to spacecoqwboy's explanation -especially he is an AE student and I#m an Economist.

Than you very mcu for the compliment, spacecowboy - your answer shows hiw worthy and correct my general knowledeg seems to be tedning.

siggy, I,ll try to demonstrate what way I have been explaining it to myself - it's in principle a mathematic especially geometrc way thats a liitle bit away from being exact:

I imagine to be in the inner side of a torus - the torus is moving in the orbit and I,m in that part that' at the site opposite to the direction of move. I just have arrived from outside at that placed and my own modings are not coordinated to the move of the torus - I#M moving to the identical direction but not as fast as the torus. The consequence is, that the outer wall of the torus is approaching to be - so I will lie at that outer wall or I will stand on it. becuase the wall and I myself will sligthly collide. If I can't see through any window I will "feel" this like I've fallen onto the earth and landid at my feet or my back.

Now this won't be sufficient if I would decide to move within the torus because at that part 90 degrees further the outer wall would be parallel to the direction of the move of the torus - tat that part the wall wouldn't be "pressing" to my feet or my back.

To have artificial gravity there the same motion relatively to me is required than at the first considered part. There are two alternatives to achieve this - another direction of moving myself or a move of that second part of the torus. But these both alternatives can be combined. After the first considered part of the torus has been colliding to me the torus should be set into rotation. Aslong I'm touching the outer wall with my back or my feet or some other ppart of my body the wall will be permanently changing the direction of moving myself because of the rotation - and all parts of the outer wall will be moving in the same direction. All these changes of direction will be accelerations into a new direction. If I lift one foot and place it to another point the rotation will cause the outer wall to move to my foot. The orbital motion of the torus within the orbit will contribute the rest.

Writing all this I'm looking all this like a movie in my head so I cannot take a video of it. but try to draw graohics of it. In my imaginations the orbit is connecting the side of the torus being in opposite to the direction of orbital motion to that side being in direction of motion - but all is valid too if the orbit is vertical to this connection I think - but the expalnation will be a little bit complicated.

If you find yuorself failing in drawing the graphics I will draw and scan them to post them here.

Conderning the requirement for artificial gravity there are medical reasons. If there is no gravity for along time all bones of the beings will be reduced and decreased. This would cause reduced ability to live under gravity - it really could end up with unability except lying in bed.

Partially the consequences of absence of gravity today already can be handled by medicines or something similar.

Recently I read that a problem discussed a long time was the Coriolis force but it has been found out that the brain is neutralizing the force. So it's no major problem - it could be handled by some training and the diameter of the torus copuld be chossed wide.

siggy, not o forget your ´question cincering the similarity to space elevators: The counterweight at the outer end of the elevator is rotating around the inner end at the center. So someone being inside the counterweight touching the outer wall - that wall not being at the side of the center - will experience artificial gravity. It's really the same as the astronauts cabin connected to a rotating part of the engine in the case of the spacship travelling for the Mars The only difference is that there is nothing clmbing along the cable.



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Post    Posted on: Sat Aug 21, 2004 10:50 pm
siggy wrote:
I doubt old people are 'fit' enough to go around in zero gravity.

:roll:
wirehead wrote:
Really, the fun one is getting the old folks up into space, not when they are actually there. And, in either case, the part that sucks is going back to gravity after a long time.

that's why we'll be running the hamster wheels when we're not free-flying

-- future old person

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Post    Posted on: Sun Aug 22, 2004 4:58 am
And you would think we would get away from the rat race.


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Post    Posted on: Sun Aug 22, 2004 8:41 am
Thakns for the explanation Ekkehard Augustin :)


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