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John Kierein
2003-Feb-07, 04:01 PM
22 hours in a centrifuge at 3 g's.
http://science.nasa.gov/headlines/y2003/07feb_stronggravity.htm?friend

David Hall
2003-Feb-07, 06:15 PM
Woah...heavy, man. /phpBB/images/smiles/icon_razz.gif

Waarthog
2003-Feb-07, 06:21 PM
My head is spinning. /phpBB/images/smiles/icon_lol.gif

traztx
2003-Feb-07, 06:30 PM
This seems odd:

http://science.nasa.gov/headlines/y2003/images/stronggravity/rotate_med.gif
(from the article mentioned above)

Why build a truss when 2 cables would do the trick just as well and are easy to deploy?

g99
2003-Feb-07, 08:24 PM
But the problems with cables is them whipping around when you (for some reason, emergency or otherwise) want to stop the rotation. Say you want to dock up to one of the external capsules to get something or someone. How can you do that with it spinning like that?

A.DIM
2003-Feb-07, 08:36 PM
Would a massive spinning disc work?

darkhunter
2003-Feb-07, 08:49 PM
On 2003-02-07 13:30, traztx wrote:
This seems odd:

Why build a truss when 2 cables would do the trick just as well and are easy to deploy?


As well as the above:

To mount instrumentation on could be one reason.

Possibly some expirements either "don't care" about the motion or could use it as part of the experiment...

Rue
2003-Feb-07, 08:56 PM
Could not docking be achieved like in the movie 2001? (by matching rotation and docking with the center of the truss.)

Slappy
2003-Feb-07, 09:07 PM
Quote from BA in the review of "Red Planet" re: angular momentum

"...they used spinning wheels on the ship to simulate gravity, which would work. I was amazed to see two wheels, spinning in opposite directions. This is exactly what you want to do! If you have only one wheel spinning, the ship itself will try to spin in the other direction (this is called ``conservation of angular momentum'', for those of you that love jargon). Having a second wheel spinning in the opposite sense counteracts that. Also, a single spinning wheel makes it very difficult to steer the ship, so having a second one again counteracts that."

g99
2003-Feb-07, 09:39 PM
Yes you would be able to dock with the center port in both versions. In the truss you would be able to go from the center to the external sections without stopping the craft and if needed stop the craft with limited worry about momentum and inertia. But with the cables, the external pods are tottaly seperated from the hub. The only way to get between them is to use some sort of elevator. This would then effect the pods of the craft since the elevator pulling itself up will also pull down on the external pod. You see the problem here?

So what if you have a sick or dieing crewman in one of the external pods? How would you get to them to save them without destroying or killing everyone else on the station?

I think the best option would be something like a central gravity free hub with two spiining truss's to simulate gravity for living conditions. Two opposing wheels would take too much energy and resources to create. Why not just have a two oppositely spinning trusses with crew compartments on the ends. Then to work they would go to the main hub.

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<font size=-1>[ This Message was edited by: g99 on 2003-02-07 16:39 ]</font>

traztx
2003-Feb-10, 11:49 PM
Those are good points. The reason I like cables, however, is that the separation is farther per weight of the separating structure. Therefore you can get the benefits of gravity at a slower rotation rate with less difference between aceleration of head and foot.

For docking:
1) An elevator capsule that can crawl from the habitat pod to the center of rotation. Once at the center, it can pivot the hatch into the axis of rotation. Then make adjustments to align it to the exact center and begin counter-rotation to match the interface to the other vessel.
2) Reel in the cables and spin down whenever you need to dock.

Option 2 might be good for a ship that spends several months without any docking. For example, a manned trip to the Kuiper mines.

g99
2003-Feb-10, 11:53 PM
If you are using a elevator to crawl up the cables, what keeps the elevator from pulling in the pod as it climbs the rope? What keeps it from becoming unstable and making it snap back when the elevator stops pulling?

Kaptain K
2003-Feb-11, 12:54 PM
On 2003-02-10 18:53, g99 wrote:
If you are using a elevator to crawl up the cables, what keeps the elevator from pulling in the pod as it climbs the rope? What keeps it from becoming unstable and making it snap back when the elevator stops pulling?

You are not crawling up the cable to the pod. You are crawling down the cable to the pod. In a rotating system, out is down and up is toward the center.

logicboy
2003-Feb-11, 04:03 PM
On 2003-02-07 16:39, g99 wrote:
Yes you would be able to dock with the center port in both versions. In the truss you would be able to go from the center to the external sections without stopping the craft and if needed stop the craft with limited worry about momentum and inertia. But with the cables, the external pods are tottaly seperated from the hub. The only way to get between them is to use some sort of elevator. This would then effect the pods of the craft since the elevator pulling itself up will also pull down on the external pod. You see the problem here?

So what if you have a sick or dieing crewman in one of the external pods? How would you get to them to save them without destroying or killing everyone else on the station?

I think the best option would be something like a central gravity free hub with two spiining truss's to simulate gravity for living conditions. Two opposing wheels would take too much energy and resources to create. Why not just have a two oppositely spinning trusses with crew compartments on the ends. Then to work they would go to the main hub.



You can easily counter act the elevator problem by adding a weight on the opposite end the moves in the opposite direction your moving.

---0----------O-----------0---
--------0-----o-----0---------
> <

logicboy
2003-Feb-11, 04:18 PM
There would be a Gforce increase in the above decription but a soon as you got to the other end it would be back to normal.

logicboy
2003-Feb-11, 04:23 PM
actually I believe I was right the first time
there would be no increase

traztx
2003-Feb-11, 05:59 PM
On 2003-02-10 18:53, g99 wrote:
If you are using a elevator to crawl up the cables, what keeps the elevator from pulling in the pod as it climbs the rope? What keeps it from becoming unstable and making it snap back when the elevator stops pulling?


The cables will maintain a substantial tension on them. Probably >1g * mass of one side of the system. If the elevator is much less massive than 1/2 of the system and the wheels are designed to minimize jerk (belt drive?)

R.A.F.
2003-Feb-11, 06:18 PM
On 2003-02-07 11:01, John Kierein wrote:
22 hours in a centrifuge at 3 g's.
http://science.nasa.gov/headlines/y2003/07feb_stronggravity.htm?friend

I LOVE the Gravitron ride mentioned in this link. When I go to a carnival it is the first and last ride I go on. I was a bit disillusioned to find that I've only been "pulling" 3 G's when riding it.
I'm such a wimp, I thought it was more like 6 or 7. LOL

g99
2003-Feb-11, 08:57 PM
Thanks for correcting me folks!

So what would be cheaper (or cost effective) to create and bring into orbit? Having to create a very high tensile and resistant chord or a strong structural element to hold the pods?

traztx
2003-Feb-11, 10:45 PM
On 2003-02-11 15:57, g99 wrote:
So what would be cheaper (or cost effective) to create and bring into orbit? Having to create a very high tensile and resistant chord or a strong structural element to hold the pods?


Don't get me wrong, I'm just guessing about this. Not an expert at all.

With that said...

Creating: We probably already have good enough materials in use. The cable would need to be wrapped or coated to prevent welding in vaccuum. The truss has already been done on ISS. It needs to have bolts strong enough to "carry" each end during the rotation. The load during rotation is as if you were suspending one end here on Earth (assuming roughly 1g).

Bringing: Just a matter of weight.

Deployment: Truss would be built in 0g either by robot or EVA. Cable deployment would be done during slow rotation (just enought to keep it good and tight), possibly without robot or EVA. Just detach and unwind.

Another benefit of using cables is that you can run power and communication through them. So you could design a reactor on one end and a habitat on the other. Maybe have a lab in the middle or something.

Lexx_Luthor
2003-Feb-12, 06:24 AM
Two craft with independant manuevering and attitude control tied together? Put them a mile apart and have them thrust in opposite directions and the cable might make them rotate about a point between them (with possible corrections from the craft's thrusters until a more or less stable rotation is made).

more or less? /phpBB/images/smiles/icon_biggrin.gif

I mean, two objects passing in opposite directions add their angular momentum about a point between them. The cable can keep the system's angular momentum constant by not allowing the craft to get farther apart but make them rotate instead.

(I'm making all this up right now)

And because the two craft start up with velocities tangent to the cable, the jerking or "stress" (I'm now being terrorized by my first mech material class) may not build up fast so maybe the cable could take the SUFFERING--my prof calls it "strain" for some reason.

I dunno what I'm talking about /phpBB/images/smiles/icon_biggrin.gif

traztx
2003-Feb-12, 03:38 PM
On 2003-02-12 01:24, Lexx_Luthor wrote:
...Put them a mile apart...


Shhh... don't let your professor hear you speak in English units! /phpBB/images/smiles/icon_eek.gif