Polywell + Space Elevator = Hyper Cheap Access To Space

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BSPhysics
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Polywell + Space Elevator = Hyper Cheap Access To Space

Post by BSPhysics »

Some of the hangups with the Space Elevator are extemely high powered lasers, the guidance of the beams through the atmosphere, the PV cell conversion efficiency, and other factors. If a polywell reactor could be placed on an aircraft why couldn't it be placed on an elevator to power it into space? It would completely eliminate the headache with lasers. With power to boot, the elevator cars could go much faster than with laser power. When the elevator reaches it's destination it could be tugged (more polywell power) over to another ribbon and brought back down to go again.

Dr. Bussard made it known that fusion engines could get to Mars in a month. If Mars spaceships were flung from 100,000 km away from the equator at more than escape velocity, how much more quickly would a trip to Mars or the outer planets be?

Also, right around the time compact BFR's are coming of age, large scale, cheap manufacturing of carbon nanotubes may be possible. The timing of each technology may come together in say 15-20 years.

Just a thought, I'm curious what the board thinks.

BS

Tom Ligon
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Post by Tom Ligon »

There are several big obstacles to a space elevator other than the basic technology of the cable and power system. I'm not saying it won't work or that the Polywell would not be a key player.

Point one is you can't build a space elevator from the ground. You have to build it starting at geosynchronous orbit. Simultaneously drop one cable while paying out a counterweight to a higher orbit. That requires conventional launch capability, plenty of it, and affordable. That suggests to me that Dr. Bussard's basic rocket ideas will be exercised first, and would be a key to making it work.

Point two is, there are no half measures in a space elevator. You can't build one half-way or a tenth of the way, it has to go all the way. And if you want it to carry people, it needs to be big enough and robust enough to protect them from radiation as they climb slowly thru and out of the Van Allen belts. This is a huge undertaking. Human nature says we won't do it in order to get into space. Instead, we'll need to be in space in a big way in order to justify building it so we can get into space cheaper and using less precious reaction mass. Space has to already be viable in order to do this to make it more viable. Again, rockets will do it first.

The third obstacle is the thing would be frightfully expensive. You need a thriving economy to support the effort. I'm optimistic on that, too.

The main obstacle to all this right now may be riding on receipt of a large power supply. C'mon, c'mon, c'mon!

Nanos
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Post by Nanos »

I wonder what a rough idea on cost would be ?


I did notice chatting to some greens the other day, they actually rather liked the idea of it, that and if you had several of them and used them to travel around the globe instead of aircraft.

Though I'm rather fond of the atmospheric/vacuum railway system approach myself, particularly as you could move the engines away from the train and to the stations .

BSPhysics
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Post by BSPhysics »

Thanks for the input Tom. The synergistic effects of both the elevator and compact, fusion power may have a few important contributions. First, the rocket power to lift the ribbon would be much cheaper if they are powered by BFR's instead of chemicals. Brad Edwards' concept is to lift a spool to GEO and unroll it both up and down. The elevator wouldn't be complete when unwound, it would be far to heavy to lift. But a climber on an ocean platform at the equator would climb up attaching more and more width to the ribbon until complete. Fusion rockets help the initial cost go way down.

The Van Allen belts are a huge issue. Would doubling the elevator car's speed, providing a little EM shielding and a thin water jacket eliminate most of the problems? With lasers, these options are impossible.

Again, just more thoughts and thanks for the input.

BS

Keegan
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Post by Keegan »

BSPysics do you know how massive, a unit of force, a Gigapascal is ?

The most super advanced materials currently in development have tensile strengths 10's of Gigapascals short of current estimations of the ribbons required strength. These materials are made in laboratories and rarely exceed millimeters in length.

The space elevator's ribbon will, in contrast need to be 37,500 kilometers long.

This for me is kinda a deal breaker, which is why i started to consider more viable megascale engineering projects

Though i wholeheartedly agree. A fusion powered electric launch system would advance mankind by leaps and bounds. Truly a richeous challenge.
Purity is Power

Roger
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Post by Roger »

Tom Ligon wrote:
Point one is you can't build a space elevator from the ground.
All the sci fi I've read had 'em started in orbit, My fav was moving a suitable asteroid into orbit, build a base there, and mine the roid for materials to be used in the elevator, lowering the elevator as its manufactured. I think from Kim Stanley Robinson's Mars series.

Getting a polywell onto an orbital station, or to the moon is a huge step. But an elevator is even farther away, we need the industrial capacity in space, to support an elevator project.
I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

cuddihy
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Post by cuddihy »

Tom Ligon wrote:There are several big obstacles to a space elevator other than the basic technology of the cable and power system. I'm not saying it won't work or that the Polywell would not be a key player.
<SNIP>

Point two is, there are no half measures in a space elevator. You can't build one half-way or a tenth of the way, it has to go all the way.
That's entirely not true, Tom. I did my Master's thesis on space tether applications, one of the interesting ones is to do just that --build a tether only a small length (several, 20-30 km long), put it in a slightly elliptical high LEO orbit, spin it up to several times orbital rate, and use the tether system's angular momentum to boost a suborbitally-launched payload to orbit. .Here's a paragraph from the survey portion of my thesis:

5. Momentum Exchange – Electrodynamic Reboost System: MXER
Probably the most technically challenging and futuristic proposal for the use of space tethers (outside of the reality-challenged space elevator) is the proposal to use large, rotating tether systems in orbit to boost payloads from low, to higher orbits. NASA’s In Space Propulsion Program (ISPP) is charged with developing technologies that could lower the cost of spaceflight. Under that aegis, the Momentum Exchange – Electrodynamic Reboost system has been proposed as a reusable system which would be placed into an eccentric Low Earth Orbit (LEO). The MXER tether system would rotate in such a way that, although the MXER center of mass (CM) would be in a higher orbit, the tip of the rotating tether would match the orbital speed of objects at the lower orbit (see Fig 6). MXER captures the payload in the lower orbit, and transfers a portion of its momentum to the payload, placing it on a GTO or higher orbit. The momentum transfer necessarily lowers the orbit of the MXER system.

Figure 6. MXER Capture / Momentum Transfer (TUI)

To make it reusable, the orbit of MXER has to be re-boosted after each use. This is accomplished by using EDT propulsion to slowly restore the orbit. With an extremely large scale, and using the apparently “free” power of EDT propulsion, the concept has fired the popular imagination. Admittedly, the proposal is dependent on several TS technologies and operational modes that have yet to be proven. Among the challenges and unknowns are:
1. Control of a large, rotating tether in orbit, including how to stably “spin up” the tether system, and maintain its spin over time.
2. Developing solar arrays that can track the sun with the tether rotating.
3. Electricity storage systems that can store the required energy, and then rapidly produce the high currents required to boost the system.
4. Predicting and controlling the tether and payload orbits so that rendezvous and capture can be accomplished in the small window such a system requires.

Figure 7. MXER Tether Concept (Bonometti)

Many other unstated challenges exist. The MXER concept is seen by most as something futuristic, or at least technically impractical in the near term. In the mean time, however, the MXER program has developed several useful technologies that have application to other tether system projects. In particular, the study of survivable, strong, conducting tethers, the development of the “Canfield joint” that allows 360˚ tracking without slip bearings, and the continued study of bare wire tethers, have all been important contributions to space tether research.
so there. You can do "half a space elevator" that helps lower the cost to orbit. It's not an all-or-nothing proposition.

And if you want it to carry people, it needs to be big enough and robust enough to protect them from radiation as they climb slowly thru and out of the Van Allen belts. This is a huge undertaking. Human nature says we won't do it in order to get into space. Instead, we'll need to be in space in a big way in order to justify building it so we can get into space cheaper and using less precious reaction mass. Space has to already be viable in order to do this to make it more viable. Again, rockets will do it first.

The third obstacle is the thing would be frightfully expensive. You need a thriving economy to support the effort. I'm optimistic on that, too.

The main obstacle to all this right now may be riding on receipt of a large power supply. C'mon, c'mon, c'mon!
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Tom.Cuddihy

~~~~~~~~~~~~~~~~~~~~~
Faith is the foundation of reason.

Roger
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Post by Roger »

TC, you are talking about slingshots...

A far cry from an elevator. A geo sync 24k miles up elevator, correct me if I am wrong... must me built in orbit, then lowered. Period.
I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

cuddihy
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Post by cuddihy »

From an orbital mechanics perpective, they are the same thing. In each case you are trading angular momentum of one orbit for another. I.e., you're not actually "sligshotting" the lower craft so much as catching up to it, trading momentum, and then letting go.

The only purpose of the tether system rotation is to match the orbital rate of the lower object. In a space elevator, the orbital angular rate is just so slow that it matches the earth's rotation rate. So if you trade momentum with a space elevator, by climbing up the rope, somehow you have to add that momentum back in or the elevator will drift towards earth. Most schemes accomplsh that by a "counterweight" past geo that adds that momentum back.

By the way, 17,000 miles is a long way to travel on an elevator.

25,000 miles for the counterweight is even further.
Tom.Cuddihy

~~~~~~~~~~~~~~~~~~~~~
Faith is the foundation of reason.

cuddihy
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Post by cuddihy »

By the way, if you want more detailed information on MXER, google "MXER Bonometti"
Tom.Cuddihy

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Faith is the foundation of reason.

Roger
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Post by Roger »

TC you're picking nits. TL is talking elevator, you are talking tether.

APPLES AND ORANGES.

TC if you think for a moment that Ligon doesnt know what you are talking about then you are sorely insulting him.

TC you make a valid point, very valid, and old, but moot to TL's post. I call it conflating.
I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

Roger
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Post by Roger »

I dont see it happening like that.. no way.
BSPhysics wrote: Brad Edwards' concept is to lift a spool to GEO and unroll it both up and down.
I'll bet you a dollar that when it gets done, the elevator will be built in orbit, using an asteroid placed in orbit for resources. Placing a tether factory powered by a polywell on the rock.

Even a feather weight ribbon 23k miles long is not going to be "lifted" anywhere.

IMHO its far more important to build industrial capacity off planet, because lifting things off the earth is just a silly thought in the long term. One could spend a lot of planet wide economic capacity to build lift capability, or one can put that effort into space based industrial economy.

Once one builds industrial capacity off planet, lifting large things to orbit just isnt needed if one can build what one needs ... in orbit.
I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

Nanos
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Post by Nanos »

Do you think prizes like the Google X prize will help encourage development to industrialise space ?

(Sadly, even some greens I speak to are against it, I tried pointing out there is no wildlife on Mars to worry about..)

MSimon
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Post by MSimon »

50E6 meters * 1 g/meter = 50E6 g = 50E3 Kg = 50 long tons.

Do able. It might tale a special vehicle.

Worth while? Different question.
Engineering is the art of making what you want from what you can get at a profit.

cuddihy
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Post by cuddihy »

Roger wrote:TC you're picking nits. TL is talking elevator, you are talking tether.

APPLES AND ORANGES.

TC if you think for a moment that Ligon doesnt know what you are talking about then you are sorely insulting him.

TC you make a valid point, very valid, and old, but moot to TL's post. I call it conflating.
R, First of all, Tom Ligon's a big boy and I doubt is insulted by accurate contradiction.

Second, i'm neither picking nits on a single post or "conflating," whatever you think that means, I'm commenting on the central topic of this thread. A space elevator IS a space tether system.

If you took offense at the "reality challenged" comment from my thesis (which I wrote over four years ago), I apologize, it wasn't written for general release at the time and I wasn't trying to provoke by reposting it. That said, a space elevator is indeed WAAAAY outside of existing possible technology, and I don't understand why many proponents of the space elevator are simultaneously completely dismissive of smaller tethers, despite the fact that they are perfect testbeds for much of "space elevator" technology.

It's a bit like fusioneers who are dismissive of IEC fusion because non-Maxwellian is "small ball."
Tom.Cuddihy

~~~~~~~~~~~~~~~~~~~~~
Faith is the foundation of reason.

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