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Yet another nutty launch scheme.

Posted by: BEM - Thu Dec 22, 2005 10:50 pm
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Yet another nutty launch scheme. 
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Post Yet another nutty launch scheme.   Posted on: Thu Dec 22, 2005 10:50 pm
Hi all,
I figured this was a topic for the space cafe rather than the technology forum since there is enough real tech out there to fill several forums, and some real rocket scientists talking about it.

How about a low orbit monorail for catching craft just above the atmosphere, and propelling them into a high orbit?

I did a rough calculation once (I mean pre university) which suggested you needed about an order of magnitude more effort to reach orbital velocity than merely to get above the atmosphere (?anyone confirm/deny this?)

The monorail would have to be pretty long, but unlike eg space elevator, there is no inherent stress on it. its all in freefall. In fact, the monorail does not even need to be connected. It could be a series of discrete magnet-bearing satellites, each with their own solar powered ion drives for gradually recovering velocity. (?hey, is there such a thing as a low orbit ion drive that can operate perpetually by using atmosphere ions for thrust?)

Also unlike a space elevator, the entire structure can survive individual elements failing.

The monorail could perform four types of acceleration.
1. accelerating a craft from earth velocity to monorail velocity
2. accelerating a craft from monorail velocity up to a higher orbit.
3,4 perform the reverse, deaccelerating a craft back to earth velocity.. (none of this entering atmosphere at 18 times speed of sound! Also recovering the monorail's own momentum)

If the monorail formed a complete circuit of the earth, there would be no need to accelerate at any particular rate. In fact perhaps you could just have a geostationary 200k tether down from the monorail into atmoshere dense enough for conventional craft to latch on to?

What would it cost to get this monstrosity into space? At least you would not need to send people up with each segment. Just shoot them up there with a big cannon or whatever. They get themselves in order, and even when the monorail is just a few kilometers in length, it can already contribute in accelerating each new section up to orbital velocity.

btw, I picture each element looking a bit like a butterfly, with wings being solar collectors and the abdomin being a short rail segment. It has to be symetrical or giving a craft a push would start it spinning.


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Post    Posted on: Fri Dec 23, 2005 6:33 am
If the mono rail in in orbit at 200 km, each segment is moving at about 7.5 km/s relative to the surface of the Earth or any rocket that just 'pops out' of the atmosphere. Unless you have a car riding the mono-rail backwards at 7.5 km/s, nothing is geo-stationary.

So do you have cars that accelerate to orbital velocity relative to the rail, but zero velocity relative to Earth, dock with a sub-orbital load, then accelerate back to orbital velocity?

A better way might be a counter-rotating tether.


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Post    Posted on: Fri Dec 23, 2005 10:52 am
Hi Wannabe,

(im relabeling this idea skyrail, probably more accurate than monorail)

yes, that is what I meant, the cable stationary with respect to the earth's surface, but moving at great velocity wrt to the skyrail. I figure there is no physical contact with the skyrail, all magnetic, so potentially no friction.

However the cable idea was really just a side-note, an example of an extreme case.

The counter rotating tether certainly might be a better idea. It was developed by someone far more qualified than me! But of course I am much more interested in discussing the merits of the skyrail here. Call it rampant ego. :P

advantages of the skyrail could be a less stressful ride, no particular requirement for advanced materials in its construction (I mean there is no necessary issue of pushing tensile strength and human gee-force tolerance to its limits for more efficiency etc), and a modular construction that can survive units dying. There might be some advantage in the fact that you can reguard the skyrail as a stationary object in terms of navigating to connect with it, so long as you dont touch it, in which case it becomes a chainsaw.

Can anyone speculate on how the magnetic 'grappling' could work? It has to do two things: 1 counter the force of gravity, 2, acelerate bodies along its length. Could more upwards force be delivered with less rail mass because it is rushing past so fast?


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Post massivity   Posted on: Mon Dec 26, 2005 6:31 pm
if you make individual parts of the rail really massive, then the rail will decelerate very slowly when pushing along a vehicle or cargo. An ion engine can the recelerate the rail. Is anyone out there willing to do the math (i.e. an excell graph of mass of rail vs. acceleration and distance fallen before stopping of deceleration with an ion engine)?

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Post    Posted on: Tue Dec 27, 2005 11:45 am
Hi SuperShuki,
Im hoping it wouldnt need to be massive at all, at least individually. Each element might only give a small nudge, but remember that they are passing at several kilometers per second, so if they were separated by 10 meters, there would be several hundred nudges per second.

One thing to note also is that to merely grab onto the rail (in a frictionless manner) in order to prevent oneself falling back to earth does not reduce the velocity of the rail because the force is at right angles to the velocity of the rail.

Pulling on the rail to accelerate a craft will change the rails velocity, but this change will be spread over the entire mass of the rail which is probably much more massive than any one craft, and the process of deaccelerating craft back to geostationary when they return to earth will reverse this velocity change.


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Post    Posted on: Thu Dec 29, 2005 9:54 pm
Were you thinking of this?
www.launchloop.com

Once again--you need massive infrastructure.

I know you get tired of me harping on this--but whether its VLAs or HLLVs or massive systems like launchloop--we are never going to have tiny spacecraft like what you see in the movies.

Space requires blue-collar thinking of a whole other scale.


Less MSN, and more TVA...


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Post    Posted on: Fri Dec 30, 2005 4:23 am
Thanks for that link, publiusr

Thats very similar, and should answer a bunch of questions I had.

And also I was going to mention idea of building a vaccum-encapsulated loop around the equator on the ground, and just charging it up with kinetic energy. That is pretty much identical to this idea.

No idea how much that sort of cable would cost per kilometer, but it is interesting to note that there is no excessive strain anywhere and potentially no inefficiency or wear. It still has the major flaw that if any part goes, they all go I guess.

My original skyrail idea has the advantage of being much better able to recover from failure, and would be of use even before finished (initially the structure would only need to be big enough to accelerate its own components, but later it could pack more densely) but has the disadvantage that you have to get each element into orbit in the first place, and then you still have to get high up enough to grab onto it.


Quote:
I know you get tired of me harping on this ... we are never going to have tiny spacecraft like what you see in the movies


I dunno, tiny spacecraft seem to be pretty common. The real technical hitch is tiny people ;)


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Post    Posted on: Fri Dec 30, 2005 10:15 pm
More do-able:

Moon launch
http://forum.nasaspaceflight.com/forums ... 2&posts=10

But you need HLLV to put THAT up there.
No getting around the need for big rockets like this:

http://www.marssociety.de/html/index.ph ... 0000000000

OT DNA
http://www.newmars.com/forums/viewtopic.php?t=4113


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Post    Posted on: Fri Dec 30, 2005 11:59 pm
Quoting myself from earlier in this thread:

Quote:
The counter rotating tether certainly might be a better idea. It was developed by someone far more qualified than me! But of course I am much more interested in discussing the merits of the skyrail here. Call it rampant ego.


Qualitatively these approaches all have their own merits.

I guess I am more interested with playing around with some formula to estimate the effectiveness of my idea. (And I quite expect that once I start playing with numbers, to find reason to abandon the idea quickly myself)

Thanks for that earlier link. It might have the sort of details I need.

My feeling (before looking at the numbers) is that my idea would never bootstrap us into space, but might still eventually be the most attractive when our orbital launch requirements mature. I feel it is more reasonable than a geostationary elevator for example.

Re the very large rockets.. I guess so, but am more interested in how small a self-sufficient colony can be. They are both topics that deserve their own threads.

I think I will go away and read that earlier link and see if it answers some of my quantitative questions.


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Post    Posted on: Sun Jan 01, 2006 2:44 am
Ok back again after looking more closely at that link.

Realised I have a big problem. The point is that this rail has to be very light per meter to be practical, eg grams or less. I was hoping to some how gain 'leverage' from the fact that the elements are moving past at a great rate.

This is true for, say, a stream of water. The faster it is moving, the more presure it exerts on your hand, either push you hand up to its velocity, or to deliver a sideways force if you hand is angled to deflect the water.

However it does not seem to be true of grabbing a rail with a magnet, as far as I can tell. All that matters is how much iron you have to pull on at any instant.

I expect it is true for a charge, ie if the rail were charged plates deflected by a magnet on the craft, but also I expect that orbital speed is small compared to the speed of electricity moving through a wire, so no spectacular gain can be expected there.

One hope: Although at any instant we would only have perhaps grams to grab onto electromagnetically, these grams would behave as if they had much more inertia when trying to deflect them sideways. Does this give any advantage?

Another hope is that if the 'rail' was a series of plates that accumulated a small static charge, a ship brushing by could have a pretty high current to make use of.

Any engineering types got any input to this problem?


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Post    Posted on: Fri Jan 06, 2006 11:33 pm
With the amount of infrastructure you need for huge lasers, launch loops, etc.--you'd be better off--and save money--just by buckling down with HLLV. People are going to have to put aside Rube Goldberg contraptions and learn to love the big rocket.


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Post    Posted on: Fri Jan 06, 2006 11:57 pm
Hi publiusr,

I am interested in debating this with you, but this is not the thread for it. Could you start a new thread or point me to an existing one?

The question I am most interested in (for this thread) is for someone whose physics is a little fresher than mine: Is there any way to 'grip' a rail more efficiently electromagnetically because it is moving past you rapidly?. By 'grip' I just mean get a superior kick from, especially in a direction normal to the rail.


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