Prophesy Designs

[Jay-qu]

This is a thread to put all designs, pictures and related concepts pertaning to the overall design of the space ship The Prophesy

[arkain101]

eeeeexcellent..... *rubs hands together*

 

let the designing commense

[ronthepon]

Look, people, I hope you shall be attaching all the source files you can along with this too. (Like arakain101's HL *.map files)

[TheBigDog]

The following are a series of PM's exchanged between myself and Janus (used by permission) around some of the engineering that is described in the stories...

[TheBigDog]

PM from Janus (with permission)

I hate to keep being a wet blanket, but:

 

As the ship begins to accelerate the modules of the outer ring turn at their couplings to keep the g force always straight into the floor.

There is no way to keep a normal g-force to all floor surfaces at all times.

 

We can either have normal force during thrust, or during no thrust. We will just have to live with having a slightly tilted floor during certain parts of the trip.

 

This is one reason why I avocated a low thrust (.01g) for our ship. At this thrust, we only have to deal with a 0.5 degree tilt from normal.

 

 

In the construction phase the spokes that connect the chassis to the ring were actually crawl tubes used by maintenance personnel. They were sealed off after the ship was completed. In the final months we had made use of these 24 tubes. We put a computer controlled system of weights into them. These weights sit nearly fully extended at the beginning of the trip. As the ship rotates the weights can be pushed out and in to disrupt the balance of the ship, making her wobble. By doing this fast enough and in the correct timing you can use the natural spin of the ship to change her orientation.

 

Sorry, but this won't work. Sure, you can shift weights around and cause the ship to "wobble", but all this will result in is causing the crew to stagger around like drunks and induce a few cases of motion sickness.

 

The ships and the weights are a closed system, with a given total angular momentum. If you move parts of system around you can redistribute the angular momentum from one part of the ship to another, but the total angular momentum of the system remains the same.

 

Flipping the ship such that it points in the opposite direction is the equivalent of changing the sign of the angular momentum of the total system. IOW, to do such, you have to change the total angular momentum of the system. You cannot do this by simply shifting weights along the length of the spokes, That would result a vilolation of the conservation of angular momentum.

 

There is a way around this however, If we put a massive fly wheel in the main body of the ship and spin it very fast in the opposite direction of the ship, it's angular momentum will be the opposite of the ship's and the net angular momentum of the system will be zero (The fly wheel mass will, by necessity, be much smaller than the ship's, but by spinning it very fast, we can make the magnitude of the angular momentum equal to that of the rest of the ship.)

 

Now, we can turn the ship without any angular momentum issues

[TheBigDog]

Reply to above PM...

 

Never a wet blanket Janus. Half the fun of this is figuring out how it would actually work. I am happy for the advice.

 

Let me give you two examples for what lead to those descriptions.

 

I have a bucket full of water. When stanging still it hangs dwon straigt beside me. When I begin to turn in a circle the rope lifts up away from me at an angle. The water in the bucket remains level compated to the top of the bucket the whole time. The rotation of the modules works the same way in reverse. We start out spinning with the bucket out to the side. but we are in an elevator. As the elevator rises it adds to the dynamics. The angle of the rope lowers when we accelerate up, but the water remains level with the top of the bucket. They don't tilt very far. Just enough to compensate for the acceleration. The gforce increases, but our weight is always pointed down.

 

For the other I am thinking of a swingset. From a sitting postion on a still swing you can pump it to make it go. The action of stretching back and leaning forward timed properly makes the swing go higher and higher. The weights in the spokes work on the same principle. As a weight is sent out that area of the ship gets heavier that the opposing side. As the ship continues to rotate the weight is pulled back in and the next weigt extended. This continues all the way around keeping one relative point of the circle heavier than the other side. By timing this correctly you would take normally random wobbling and channel is into controlled movement. It would be very slow to keep the dynamic force it is creating low.

 

I think this would work. My alternative was to install large gyros inboard on the ring. Then use them to pitch the ship as desired. Similar to how satellites are pointed.

 

Bill

[TheBigDog]

Next PM from Janus (with permission)

For the other I am thinking of a swingset. From a sitting postion on a still swing you can pump it to make it go. The action of stretching back and leaning forward timed properly makes the swing go higher and higher. The weights in the spokes work on the same principle. As a weight is sent out that area of the ship gets heavier that the opposing side. As the ship continues to rotate the weight is pulled back in and the next weigt extended. This continues all the way around keeping one relative point of the circle heavier than the other side. By timing this correctly you would take normally random wobbling and channel is into controlled movement. It would be very slow to keep the dynamic force it is creating low.

 

Bill

 

Here's the problem with the swing example. You are only considering a part of the total system. If you look at just the person on the swing, then yes, it does look like your'e getting a net angular motion from a zero angular motion. But this is not the case. What you a neglecting is that the swing is anchored to the Earth. What the pumping does is to transfer angualr momentum from the swinger to the Earth. This angualr momentum is opposite that of the the swinger and equal in magnitude. The Earth rocks back and forth around its center in time to the swing (actually it rocks back and forth around the CoG of the Earth and swinger, but since the Earth is the much more massive of the two, this Cog is for all practical purposes, the center of the Earth.) We don't notice this rocking because, since the Earth is so much more massive, it only has to rock through a very tiny angle to counter the angular momentum of the swing.

 

Now our ship is not anchored to anything outside of itself that it can transfer angular momentum to. It is a closed system in itself. Now if we start shifting our weights around we can use them to rock the ship back and forth around the CoG, but the maximum angle of this rock will be limited to about 90 degrees (about the maximum arc the weights move through as they move from end to end o fthe shaft) times the mass ratio of the weights to the rest of the ship. ( IOW, if the mass of the weights are 1/100 that of the ship, you will be able to rock the ship a litte under 1 degree.) No amount of "proper timing" of the weight shift will allow you to build up to a larger rock.

 

As for the plan of moving weights to one side of the ship as it rotates to cause net movement of the entire ship. The flaw with this is that you are assuming that the center of rotation of the ship would remain along on the center line of the ship. This is not the case. As the weight goes out, the ship shifts in the other direction relative to the axis of rotation. (If the weight goes to the Right, the rest of the ship goes to the left.) this shifts just enough of the ships mass to the other side of the axis of rotation to counter the extra force caused by moving the weight out. The Gog of the whole system does not change and the forces remain balnced. Moving the weights in and out in time to the rotation just causes the center of rotation to follow a circular path around the centerline of the ship. The forces still balance, and you will get no net movement of the ship.

 

The idea that you can, by the clever shifting of weights, induce some net movement in a closed system is an old one, and an uncountable number of tdevices to do such have been proposed. None of them have ever worked. They all fall victum to the same problem: they vilolate the laws of physics.

[TheBigDog]

And my reply to the above post...

Thanks for the help with this Janus. As soon as you reminded me that the swing was anchored to the ground it all came back in a flash. In space you need to move around the center of mass. With that huge ring turning at 113 km/h it has a huge amount of inertia. My clever engineering is only effective in fiction. Part of why I usually stick to building furniture, and other such things that just need to sit still and hold weight.

 

I happily concede both points. I wonder, would you mind adding this conversation to the Space Voyage thread? I am hoping to keep it as educational and plausible as possible. I can go back and edit the stories to change the engineering.

 

Bill

[TheBigDog]

And with that exchange, along with some input from CraigD, I make the following proposal for design change to the Prophesy.

 

In the center of the ship there is a flywheel. It actually wraps around the the center of the ship. It is driven by the nuclear reactor that supplies electric to the ship. The large flywheel spins counterclockwise. As it is powered, the opposite action is the turning of the ship. The flywheel is kept spinning at a speed that keeps the ship rotating at 3 rpm. By breaking the flywheel you in turn brake the spin of the ship. In this way we no longer need our propellant to spin and despin the ship. At the same time the counter rotating gyros nullify their relative forces. So now not only can we orient the ship with much less energy. I would suggest using additional flywheel/gyros, large, to manuver and control the orientaiton of the ship as we need.

 

Any discussion?

 

Bill

[IDMclean]

Sounds like what I mentioned way back when about using Gyros to shift the force of rotation to else where, and therefore aid in spin and despin. So sounds good.

[TheBigDog]

Sounds like what I mentioned way back when about using Gyros to shift the force of rotation to else where, and therefore aid in spin and despin. So sounds good.

You are correct KAC. And I want to insure that people get the proper credit for their input! The thread has gotten so big that I was having trouble with finding all the original suggestions on the matter. (and I was tired and ready for bed)

 

Bill

[Jay-qu]

Hence the sub forum ;)

 

Problem is we cant sort the thread out and keep it intact, ie posts cant be copied, only moved.. and I dont feel comfortable just hacking up our nice big thread when it could potentially cause more confusion than clarity

[GAHD]

Hmm, On the weights on the prophercy roll-over thing i think this article may point to some ideas...http://hypography.com/forums/astronomy-news/6907-saturns-moon-enceladus-may-have-rolled.html

[Kayra]

Hmm, On the weights on the prophercy roll-over thing i think this article may point to some ideas...http://hypography.com/forums/astronomy-news/6907-saturns-moon-enceladus-may-have-rolled.html

 

Should work if we are in a gravity well :shrug:

[Kayra]

Sounds like what I mentioned way back when about using Gyros to shift the force of rotation to else where, and therefore aid in spin and despin. So sounds good.

 

 

I still say placing a series (2 per module?) of thrusters pointing along the axis of the ship should suffice for steering. By firing them in sequence at 90 degrees to the intended direction change intended, you can actually use the precession effect of the rings to turn the ship.

 

 

If you do not do this, then you had better be prepared from some pretty severe stresses where the outer rings and the inner flywheel connect to the ship. They may be able to counter each others angular momentum nicely, but that does not meant that that momentum does not exists. Every time you try to turn the ship, those areas will be straining at their repsective load bearing points.

[TheBigDog]

I still say placing a series (2 per module?) of thrusters pointing along the axis of the ship should suffice for steering. By firing them in sequence at 90 degrees to the intended direction change intended, you can actually use the precession effect of the rings to turn the ship.

 

 

If you do not do this, then you had better be prepared from some pretty severe stresses where the outer rings and the inner flywheel connect to the ship. They may be able to counter each others angular momentum nicely, but that does not meant that that momentum does not exists. Every time you try to turn the ship, those areas will be straining at their repsective load bearing points.

With the size of the ship the load on the ends of those spokes is huge indeed. But she turns very slowly. My concern with using propellent is how much it will take. I like the idea of being able to orient the ship using the electrical energy from her reactor. It gives us virtually unlimited manuvering.

 

Bill

[Kayra]

My concern with using propellent is how much it will take.

Bill

 

 

Probably drastically less then the amount of mass in the fly wheel :shrug:

Just a guess though.

 

Redundancy as well. If even one thruster is capable of firing, turns can still be made (eventually). If that flywheel blows a bearing.. getting out and pushing would be our only alternative.

 

There is something to be said for changing course electrically though.