Screw the Space Elevator, Lets Launch Loop

If polywell fusion is developed, in what ways will the world change for better or worse? Discuss.

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Keegan
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Screw the Space Elevator, Lets Launch Loop

Post by Keegan »

As much as i love the idea of a space elevator. A cable thats 37,500 kilometers long, built out of materials that are yet to be developed seems a little far fetched for me.

I was blown away when i recently discovered the Launch Loop.

Its based on the inertia of an Iron cable 5cm in diameter moving at 14km/s to raise a launch track 80km high and 2000km long. It enables through electromagnetic induction of the iron cable, 3g of acceleration launching up 80, 5 metric ton transports per hour to Earth orbit and beyond. I invite you to read

The 1985 Launch Loop Paper

Launch Loop Slides from the ISDC2002 confernece

The thing i like about this idea is that its based on existing materials and Newtonian physics.

The whole thing is one big electric induction motor. It is fully electric and simply has a power station each end. Therefore launch costs $/Kg are tied directly to the cost of power $/Kw (Hello Polywell !) It is estimated that 200Mw are required to overcome losses and keep the cable spinning.

Using conventional materials and technology, powered by a 300MW power plant it has an estimated cost of 10 billion dollars. With a 40K ton/year capacity to LEO this equates to launch costs of $300/Kg.

A 20GW 30billion dollar version with a 6M ton/year capacity would cut launch costs to $3/Kg.

Success of Polywell Fusion power would cut this again further.
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ciphergoth
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Re: Screw the Space Elevator, Lets Launch Loop

Post by ciphergoth »

Keegan wrote:I was blown away when i recently discovered the Launch Loop.
Isn't it the most audacious idea?

My personal favourite optimistic future goes like this:

(*) Polywell fusion turns out to be a viable method of power generation. Entire world starts building zillions of the things on a grand scale; price of electricity falls so dramatically (especially in contrast to rising oil prices) that everything becomes electrically powered, and people start to do things like power tractors from long tethers

(*) A large Launch Loop is built in the Pacific

(*) It's then used to launch Roger Angel's fleet of 20 trillion solar shades to the Lagrange point L1 at a hugely reduced cost

(*) The immediate disaster from global warming is averted by the solar shade, the long-term disaster is avoided thanks to cheap Polywell electricity, and the world is saved.

MSimon
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Post by MSimon »

Once you start messing with the weather any adverse weather will be blamed on the weather modifiers.

So you have to include the cost of a lot of lawyers in your calculations. That should at least double the cost.
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MSimon
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Post by MSimon »

I remember reading an Analog article on this.
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Mumbles
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The Space Elevator, the Launch Loop, and Polywell fusion

Post by Mumbles »

Keegan wrote:Success of Polywell Fusion power would cut this again further.
Ah, but the inter- and exo-atmospheric propulsion potential of a polywell fusion based ramjet/scramjet and rocket would make it so that the loop might never be required... Invest $30 Bn for an untried MEGA-Engineering project (is there such thing as a GIGA-Engineering project), or invest a few hundred million proving fusion-based propulsion to space?... The IEC potential cuts both ways...
Keegan wrote:As much as i love the idea of a space elevator. A cable thats 37,500 kilometers long, built out of materials that are yet to be developed seems a little far fetched for me.
No, the Space Elevator only requires an exotic material (mostly focused on Carbon Nanotubes) solution to keep the mass down for start-up and growth in a chemical rocket scenario. If launch costs were reduced by polywell fusion rocketry, then launching a higher-mass starter ribbon for the Space Elevator would be financially possible.

Of course, having that same polywell fusion propulsion would also pretty much eliminate the need to build a space elevator in the first place...! Same argument I used against the launch loop. Cuts both ways...!

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93143
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Post by 93143 »

You still couldn't make a space elevator with steel or Kevlar. More mass available cheaper might somewhat relax the constraints on the ribbon strength, but you'd still pretty much need CNT.

Besides, the real strength of a fusion drive is with medium and high Isp for fast space travel. Its Isp-T/W product is way better than any deep space system we have now, but the same is true of chemical engines - they just can't vary their Isp. Taking into account the reactor's weight and practical limitations on power output due to cooling requirements, you probably need either a spaceplane or an airbreathing QED engine - or both - to overcome/mitigate the gravity losses and make a fusion-powered SSTO a good idea. It would definitely be better than what we've got, but by how much and at what cost?

In other words, I doubt we'll hit $3/kg with fusion drives, and we certainly won't do it for only a few hundred million up front. If we can build an EM launcher with current technology that goes all the way to orbital velocity and runs on Polywell power, great - let's do it. (It seems we could give ~$10 billion dollars to pretty much anyone and have a cheap SSTO launch system, but no one's sure it would be used often enough, so no one funds this stuff...)

TallDave
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Post by TallDave »

No, the Space Elevator only requires an exotic material (mostly focused on Carbon Nanotubes) solution to keep the mass down for start-up and growth in a chemical rocket scenario.
...
You still couldn't make a space elevator with steel or Kevlar. More mass available cheaper might somewhat relax the constraints on the ribbon strength, but you'd still pretty much need CNT.
Yeah, the problem isn't getting it into orbit, it's the weight vs. strength issue. To make it out of steel, it would need to be about a mile thick at the center.

CNT has just about enough strength per weight. NASA is sponsoring lifter contests, so they are taking the possibility seriously.

TallDave
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Post by TallDave »


MSimon
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Post by MSimon »

The difficulty is that the required strength is at the material limit.

The loop idea seems much better from a feasibility point of view.
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drmike
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Post by drmike »

I have not looked at the elevator concept much other than some gee whiz NASA web pages. What is the required molecular force to hold the tether together? What is the highest bond strength known for any set of chemicals? That would at least tell you if the concept is physically possible at all. I would assume somebody has figured this out already.

MSimon
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Post by MSimon »

The estimated strength rqmt is at 65 GPa. The best carbon nanotubes (CNT) we can make are right in that range.

Ultimate strength estimates for CNT are in the 120 GPa range with diamond a little better.

Obviously we need to reliably make CNTs in the 90 to 100 GPa range to give a safety factor of 1.5 (aerospace minimums).

The fact that a loop launcher can be made with ordinary steel is a big plus.
Engineering is the art of making what you want from what you can get at a profit.

djolds1
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Re: Screw the Space Elevator, Lets Launch Loop

Post by djolds1 »

Keegan wrote:As much as i love the idea of a space elevator. A cable thats 37,500 kilometers long, built out of materials that are yet to be developed seems a little far fetched for me.

I was blown away when i recently discovered the Launch Loop.

Its based on the inertia of an Iron cable 5cm in diameter moving at 14km/s to raise a launch track 80km high and 2000km long. It enables through electromagnetic induction of the iron cable, 3g of acceleration launching up 80, 5 metric ton transports per hour to Earth orbit and beyond. I invite you to read

The 1985 Launch Loop Paper

Launch Loop Slides from the ISDC2002 confernece

The thing i like about this idea is that its based on existing materials and Newtonian physics.
Discovered it some years back. Kewl concept, but IIRC it's known as "Lofstrom's Lunacy" due to its potential for catastrophic failure. Also a problem that it requires several GigaWatts of nuclear reactors.

Another review:
http://www.islandone.org/LEOBiblio/SPBI116.HTM
http://www.nas.nasa.gov/About/Education ... PBI116.HTM

Similar Concepts:
http://www.paulbirch.net/

Check "Orbital Ring Systems" 1 thru 3 and "Dynamic Compression Members." The "Partial Orbital Ring System" or PORS is a close variation on the Launch Loop.

Related concept that I much prefer for elegance:
http://yawiki.org/proc/Aerovator#11
http://en.wikipedia.org/wiki/Image:Aerovator.svg

Duane
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drmike
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Post by drmike »

Using pressure to measure tensile strength is weird, but it makes sense. So it is possible in theory any way.

I do like the Aerovator. Seems much easier to build. But I suspect it will have to get in the way of some airline and bird migration paths.

but in both cases dealing with how to maintain things and replace worn parts seems like a major problem. You'd have to have something mounted on the cable/ribbon holding the whole system and put in a repair in the middle.

Neat ideas to think about in any case!

David_Jay
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Post by David_Jay »

Using pressure to measure tensile strength is weird, but it makes sense.
Testing of materials (I am most familiar with nonferrous metals) is performed by measuring the maximum force (called ultimate strength) that a material will withstand before failure. Using Pa makes sense because the cross section is covered by the unit (for Pascal, m^2), so this value is a constant for the material, independent of the cross sectional area of the component.

The same is true in SAE units, with PSI used for yield and ultimate strength designations.
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hanelyp
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Post by hanelyp »

The launch loop looks like a nice idea. One issue I note is the need of active levitation control of the steel cable in the sheath. I'd be inclined to use an aluminum cable suspended by magnetic repulsion, passively stable. Might also improve the efficiency of eddy current coupling that accelerates the payload. But then metal fatigue is more of an issue.

I agree it would make an attractive terrorist target, among other things as a new 'tower of babel'.

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