Re: Communists on the moon !
 

hehe, Its really interesting to see how discussions can get derailed:) I read the whole post again and I saw it go from life on Mars to Europa to a discussion on Communism to the Middle east (yeah, that has to come up sometime http://forum.shrapnelgames.com/images/icons/icon12.gif )

Back to the Moon... I think space tourism could really open up space. I mean if we can make going to space profitable and fun for everyone we can eventually start channeling funds to exploration/development and colonize the moon.

Hope those Xprize guys do it soon... does anyone know when the first launch is planned for?
(better star saving up those 100 grand:) lol

Re: Communists on the moon !
 

Sure L4 and L5 are great places to put stuff if you want to send it somewhere else on the cheap, but they're not such great places to work.

Microgravity is very inconvenient. Not only is it difficult to keep humans healthy in microgravity, but it's hard to work, to move things around (inertia and torque messing with you), and many machines must be built very differently to work without gravity.

The lower gravity on the moon would still be troublesome, certainly, but it would help.

Before someone brings up the spinning-wheel space station concept I'll point out that it is very difficult to do right. The problem is that as people move through the station, the station itself will move around in space. A great deal of fuel will be needed to keep it at it's intended location.

You might remember seeing pictures of American Astronauts running around the inside of Skylab, no? Yeah, they were knocking that like box all of the place while they did that, and Skylab was not properly fitted to keep it's orbit anyway.

Since an object near either the L4 or L5 positions will be gently pulled toward the actual specific Lagrange Points, you might be able to put a spinner up there and just let it go, depending on the attraction of Luna's Trojan points to keep your station where you want it. I don't think that's such a good idea, myself, and every damn thing in the station would have to hold real still when time comes for anything to dock with it.

Re: Communists on the moon !
 

Skylab was a relativly small space craft. Anything we are likely to put at an L4 L5 point is going to be much bigger. Especially if we build something with roational motion for internal gravity. That would have to be a pretty sizeable craft with a big enough radius to eliminate the detrimental physical effects on the human body of the difference in gravity along the length of your body. So we are talking about a large station with probably a multinational effort with room for dozens if not hundreds of full time occupants. Such a station will have pretty significant mass and so will not be as affected nearly as much by people moving around inside it.

Geoschmo

[ December 18, 2003, 16:16: Message edited by: geoschmo ]

Re: Communists on the moon !
 

The problem is that it will be affected. There is no friction to keep all the little bumps and jars from building up. And this isn't just about human bodies, every piece of equipment, inventory, and even the circulation of water and air will move that baby around. Sure when compared to the mass of the relatively stationary architecture of the station they seem small, but they're always moving and it will add up.

But, as I said, the great thing about Lagrange Four and Five is that an object with an orbit close that Luna's Trojan orbit will be pulled to that specific velocity/trajectory over time. I'm just not sure this balancing force will be sufficient.

Re: Communists on the moon !
 

That's the point, they are very small, and they don't add up. Unless all the vectors are the same they don't. Equipment would be planned and balanced in such a way that the majority of their forces cancel out, and the random movements of a bunch of people going in different directions about the interior of the station will for the most part cancel each other out. The result will be a small net change in whichever direction has the largest amount of force being applied. But the net change will be well within the tolerance allowable by ordinary station keeping thrusters. Docking equipment has tolerances and extra reinforcment to allow for minicule variations, and if a particularly delicate manuver were neccesary, you could always broadcast a warning on the intercom, but I don't think it would be neccesary at all. The computers and thrusters ought to be able to easily handle it.

Geoschmo

Re: Communists on the moon !
 

I will stand by my contention that the constant, semi-random displacement forces involved in real people living their lives inside a spinning-wheel space station are sufficient to make the concept wholly impractical without significantly different means of station-keeping. Every bit of thruster fuel has to be lifted to orbit as well, and I contend, as well, that it will be expended at a fairly rapid pace.

I will allow that Lagrange points four and five may compensate for this, but I wouldn't hold that up as certain until I get a better grip on the scale of the forces involved on both sides.

As I so not expect anyone here to come up with a nice, concise, understandable model that will prove this one way or another, I'm perfectly happy to leave the discussion as it stands. I have pointed out everything I think is involved, and I think you and I have different expectations where the scale of the disturbing forces are concerned, Geo.

Of course, if someone does want to do the math and whip up a nice computer model, I would be overjoyed to get my hands on the toy.

Re: Communists on the moon !
 

<font size="2" face="sans-serif, arial, verdana">More like TWENTY four... http://forum.shrapnelgames.com/images/icons/icon10.gif

Am I old! Yeah, I got the reference to Martin Landau and Barbara Bains... http://forum.shrapnelgames.com/images/icons/icon12.gif

Re: Communists on the moon !
 

I think he is more refering to it all happening in 1999 in the original show. http://forum.shrapnelgames.com/images/icons/icon12.gif

I love old Sci-Fi in both book and movie form with their predictions of what their future our past/present would be like. http://forum.shrapnelgames.com/images/icons/icon7.gif

Re: Communists on the moon !
 

<font size="2" face="sans-serif, arial, verdana">Assuming everything stays inside the station, the center of mass will remain in a consistent position.
If you set up the station to be initially stationary at the L-points, the center of mass will remain there no matter what the people inside do, due to newton's laws.

When you open airlocks to let people and cargo in and out, you will only need to compensate once. Given a large station, and reasonable care the motions induced by external traffic will be minor.

Using an Ion thruster or even a magnetic sail to maintain stationkeeping would be very useful too. Very little thrust, but you have plenty of time and don't need to accelerate much.

Re: Communists on the moon !
 

<font size="2" face="sans-serif, arial, verdana">No, I don't think this is right either. Loser is right when he says there will be some reaction to people walking around the inside of the station. As they exert force against the deck plates to go in one direction the station will have an equal reaction in the opposite direction. I just think he's way over estimating the amount the reaction will affect the station. The difference in mass between the person and the station means that almost all the energy moves the person and almost none of it moves the station. So while there will be a force applied to the station it would be imperceptable I believe.

Geoschmo

Re: Communists on the moon !
 

<font size="2" face="sans-serif, arial, verdana">No, I don't think this is right either. Loser is right when he says there will be some reaction to people walking around the inside of the station. As they exert force against the deck plates to go in one direction the station will have an equal reaction in the opposite direction. I just think he's way over estimating the amount the reaction will affect the station. The difference in mass between the person and the station means that almost all the energy moves the person and almost none of it moves the station. So while there will be a force applied to the station it would be imperceptable I believe.

Geoschmo </font><hr /></blockquote><font size="2" face="sans-serif, arial, verdana">Ah, but they can only keep going in that direction for so long before they hit the far wall. http://forum.shrapnelgames.com/images/icons/icon12.gif

Then you cancel out the velocity you and the station had while you were on your trip.

The biggest effect you could get is if everybody ran from one side to the other all at once. (Much faster than a rotation of the station, for simplicity.)
If the station's mass is 100 times what the people total, then the people moving 100m would cause the station to move 1m in the other direction, and the center of mass (people + station) would still be in the same spot (right smack dab on the L-point where it started)

Re: Communists on the moon !
 

what it would do is viberate, maybe more, maybe less as forces bounced around inside. but, baring momentum transmitted to space dust, the viberation would center on an orbiting point.

Re: Communists on the moon !
 

<font size="2" face="sans-serif, arial, verdana">We had this discussion before http://forum.shrapnelgames.com/images/icons/icon7.gif A while back when we were talking about sending a manned mission to Mars. And I explained then that If you have a rotating enclosed space station with people inside the people inside CANNOT (I repeat CANNOT) affect the total rotation or linear momentum of the whole system. (Now I don't know what happened to space lab, maybe it was just built badly and that was the reason for its orbit deteriorating, the people inside jumping about surely weren't !) Just look at Mir... those russians had some wild parties up there http://forum.shrapnelgames.com/images/icons/icon12.gif

EXPLANATION:
Say we have a roating wheel in space and its hollow on the inside. Now lets say that we have an astronaut that starts to run on the inside of that wheel in the same direction the space station is spinning. Running like that would produce a force by his legs that would work against the space station's rotation. BUT! the overall rotational momentum of the space station and the person inside wouldn't change as this is an inclosed system with no outside forces acting upon it and the sum of the rotation energy of the astronaut and the space station would be conserved.
1. space station and astronaut spinnign together: D1 = m*r^2*W1 + a*r^2*W1
D1.. total rotational momentum at the beginning
m.. mass of the space station
a.. mass of the astronaut
W1.. beginning rotational speed
r.. space station radious

2. astronaut start running and achieves a speed of Wa=W1+dW.
D2=m*r^2*Wss + a*r^2*Wa
D2=D1 (the total rotational momentum is conserved)
and with some rearangements we can see:
Wss= W1 - (a/m)*dW
D2.. total rotation momentum at the end
Wa.. ending speed of the astronaut
Wd.. the increase of the astronauts speed over his beginning speed
Wss.. ending speed of the space station

So you see we end up with an astronaut runnin dW FASTER than the speed of the original space stations rotation AND a space station rotating (a/m)*dW SLOWER then before.

But the funny thing is that the moment the astronaut STOPS running the space station will return to ist original rotating speed W1!

Friction and all other forces produced by the astoronauts legs touching the ground of the wheel will make no difference here as this is an inclosed system and it respects the law of the conservation of momentum (linear and rotational).

If this doesnt make sense to you try to think of it this way. Lets say we enclosed you in a hollow sphere in space and gave u the task of movig it around. You woulnd't be able to do it. You could bounce off one of the walls and the spere would go the other way but the moment u hit the opposing wall the spere would stop again. And the center of gravity of the spere and yourself put together would't change in this manuever... so even if you would be in orbit around the earth you couln't deteriorate the speres orbit IN ANY WAY by jumping on the inside of the spere AS THE CENTER OF GRAVITY OF THE SPHERE AND YOURSELF REMAINS CONSTANT AT ALL TIMES

[ December 19, 2003, 08:21: Message edited by: JurijD ]

Re: Communists on the moon !
 

<font size="2" face="sans-serif, arial, verdana">No, I don't think this is right either. Loser is right when he says there will be some reaction to people walking around the inside of the station. As they exert force against the deck plates to go in one direction the station will have an equal reaction in the opposite direction. I just think he's way over estimating the amount the reaction will affect the station. The difference in mass between the person and the station means that almost all the energy moves the person and almost none of it moves the station. So while there will be a force applied to the station it would be imperceptable I believe.

Geoschmo </font><hr /></blockquote><font size="2" face="sans-serif, arial, verdana">Oh no you're totally wrong here geoschmo, and Suicide Junkie is completely right. The center of mass (gravity) of the whole system (station+people inside) cannot be changed by movements inside the station.

Think of it this way: when we exert force on the deck plates in one direction we also have to exert the equal but opposing amount on some other deck plate to stop ourselves from flying out of the space station...

so... we bounce off one wall: we start moving in one direction FAST and the space station in the other just SLOWER as it has greater mass. But the POINT of gravity doesn't change.

Say you're holding a rock in space and you throw it away... that action pushes you back when the rock flies away... BUT. The center of gravity of the rock flying away and your body flying away in the opposite direction (just more slowly) DOESN'T CHANGE .. EVER!.

Now say you and the rock are tied together with a piece of string (similar situation as if you were inclosed in a hollow sphere). When the rock is so far away that the string is taught the rock will stop as the string will pull it in the opposite direction of its movement ... BUT so will u! the rock will stop your movement throught the string too! So the result is just a change in the geometry of the system NOT in its center of gravity. And if the rock and you and the string were in orbit the orbit would't change either.

[ December 19, 2003, 08:39: Message edited by: JurijD ]

Re: Communists on the moon !
 

Ok, I see what you and SJ are saying now Juri. Actually I wasn't talking about moving the base to a different orbit, but causing it to tumble, wobble etc, which would make docking difficult. I thought that's what Loser was saying too, but I reread it and see he was talking about actually changing position in space, so I was incorrect when I supported his point there. Movement of people around the inside won't cause the base to move to a different location, but it can have a minor effect on the orientation of the base, as demonstrated by the skylab astronauts. But as I was saying to Loser originally , even that effect would be infinetesimal when dealing with a base as large as what would likely be placed at an L4 L5 point.

Re: Communists on the moon !
 

with flexible docking tubes and rotational slats to keep out the sunlight, it doesn't really matter if your spacestation wobbles on it's axis.

Re: Communists on the moon !
 

<font size="2" face="sans-serif, arial, verdana">I think it was just in a low orbit, so the very slight atmospheric drag caused it to drop deeper and deeper over the months/years without thruster boosts.

Re: Communists on the moon !
 

<font size="2" face="sans-serif, arial, verdana">NO, no, no, your almost correct, I read this real late Last night and was too tired to let you all know my master plan to solve the vibration issue...JELLO yep, thats right jello, that will take care of any vibration issue and a little treat for maintenance workers, heck there could be some radiation absorbing material added to the jello for shielding.
http://forum.shrapnelgames.com/images/icons/tongue.gif

Re: Communists on the moon !
 

Y'all are correct. I have no idea what I was thinking, it's been a while since college and I'm afraid I haven't used physics much since then.

I still think there would be problems with orientation, which would not be corrected by placing the station in a Trojan orbit, but these would be more easily corrected. They could, in fact, be corrected without the expenditure of thruster fuel, but rather through the use of a powered gyroscope driven by whatever power source the rest of the station uses.

One more thing about the spinning wheel. Small changes in the distribution of mass around the wheel will change the point around which the wheel spins. This will change the strength of the illusionary 'gravity' throughout the wheel and could cause problems for any machinery sensitive to changes in it own 'weight'. Amusingly, the more mass you put on one side of the wheel the less 'weighty' things on that side will become.

Re: Communists on the moon !
 

The mass distribution could be compensated for by pumping fluid around from point to point in the structure. There will be plenty of fluid available, water, fuel, waste products. It would be a fairly simple matter of having resevoirs at various points around the station connected by tubes and pump it back and forth to keep things in balance. We do it now on airplanes and ships. It can even be done automatically by the computers.

Re: Communists on the moon !
 

no, no, no, giant shock absorber's attached to cosmic strings!

Re: Communists on the moon !
 

<font size="2" face="sans-serif, arial, verdana">Yes that is a funny thing isn´t it:) the more mass u put on one side the less "gravity" it gets heheh.

I think that one solution is obviously for the station to be way more massive than any object that will move inside of it... And the idea of pumping fluid around it to compensate for the different mass distributin is pure genious http://forum.shrapnelgames.com/images/icons/icon12.gif

Well if we get back to that Mars mission we were talking about a few months back... I think that now everyone agrees that we could build a rotating section on a spaceship that would enable people to have a semi-gravity environment. So...I have a couple thousand euros on my bank account... lets start putting money together and get this baby up in orbit before Xmas http://forum.shrapnelgames.com/images/icons/icon12.gif

because in my view the biggets problem was providing "gravity" to the astronauts. I wonder how much a say 1km wheel would cost...