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Speculative - cislunar transport infrastructure, 2054

Posted by: Centrillium - Thu Jan 19, 2006 3:49 pm
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Post    Posted on: Fri Jan 20, 2006 6:55 pm
Centrillium wrote:
I (with help) actually built a Farnsworth-Hirsch fusor last year, although it was a fairly feeble effort (we never got any neutrons).
You didn't say what elements you were using, but with hydrogen and boron you are not supposed to get any neutrons. All the reaction products are charged particles.

Ekkehard,
Freeman Dyson's 1968 idea used actual nuclear bombs and cannot be compared to the pulsed fusion drive you love to talk about so much. Dyson's idea could have been built in 1968 using off the shelf military bombs, the pulse fusion idea would require a type of fusion process that has not yet been achieved and could conceivably be proved impossible with further research.


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Post    Posted on: Fri Jan 20, 2006 10:53 pm
campbelp2002 wrote:
Centrillium wrote:
I (with help) actually built a Farnsworth-Hirsch fusor last year, although it was a fairly feeble effort (we never got any neutrons).

You didn't say what elements you were using, but with hydrogen and boron you are not supposed to get any neutrons. All the reaction products are charged particles.


Deuterium - the cross-section for p-B11 is pretty small even at 20 keV (that was about where we were working), but DD reactions should be plentiful. Our problem was the vacuum pump - we were trying to pump down the chamber with an old rotary pump and it really wasn't going to cut it. If there had been more time my supervisor might have been able to borrow a turbopump from one of the experiments in the lab, and then we might have got somewhere.

campbelp2002 wrote:
Freeman Dyson's 1968 idea used actual nuclear bombs and cannot be compared to the pulsed fusion drive you love to talk about so much.


Hee. :) Yeah, I wasn't thinking of Orion here. :)

campbelp2002 wrote:
the pulse fusion idea would require a type of fusion process that has not yet been achieved and could conceivably be proved impossible with further research.


I don't think that's fair to ICF - its pretty clear that an ICF power plant is physically possible. Its less clear whether it would be economical, given the need to manufacture the fuel pellets in enormous numbers, but obviously that's less critical in the context of space propulsion. MCF is definitely the better bet at the moment, though.


Hmm - this fusion discussion has been interesting, but sort of distracts from the main thing I originally wanted to ask, which was about cislunar transport! I'd still love to hear what people think about that.


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Post    Posted on: Fri Jan 20, 2006 11:38 pm
Centrillium wrote:
Hmm - this fusion discussion has been interesting, but sort of distracts from the main thing I originally wanted to ask, which was about cislunar transport! I'd still love to hear what people think about that.
You might take a look at the lunar tourism thread.
http://www.spacefellowship.com/Forum/vi ... php?t=1064
There I propose a 2 step architecture. One vehicle from Earth takes you from the ground to LEO and from LEO to the ground. Another vehicle takes you from LEO to the Moon and back to LEO. This is because, from and energy standpoint, LEO is the half way point in a round trip from the surface of the Earth to the surface of the Moon. I assume the lunar vehicle would use propellant produced on the Moon, or in space from asteroids. Also I consider the possibility of the lunar vehicle aerobraking into LEO in the aerobraking and reentry thread.
http://www.spacefellowship.com/Forum/vi ... php?t=1488


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Post    Posted on: Sun Jan 22, 2006 8:12 am
I'm glad to see someone else came up with my two-stage idea for a Lunar transport system... That's very reassuring, actually.

Fusion is very good for Lunar transportation, but is much more important for Mars missions. We can probably get by with chemical rockets for early Lunar missions: space will still be a novelty, as will 0g (in this case, nearly true free-fall). Chemical rockets might actually be *better* than fusion rockets (which would use a constant acceleration -- much much more efficient, but even less attractive from a travel agent's point of view).

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Post    Posted on: Sun Jan 22, 2006 9:55 am
To give a hint to the context, Peter,

I mentioned Dyson simply because he explicitly said that the pulsed fusion drive would have reduced the costs very much,

I have written several posts in a few other threads where I explicitly several times explicitly said that there is one concept using fusion bombs while another is using micro-explosions ("Mikroexplosionen" - directly quoting Ulrich Walter),

I have been speaking in this thread myself of the micro-explosions propelling the vehicle by impacts into a magnetic field while the concept using fusion bombs would have impacted plates,

I also have posted in other threads that the micro-explosions impacting magnetic fields are used for Daedalus,

and both the concepts - Orion with nuclear bombs and impacting plates as well as Daedalus using micro-explosions and impacting magnetic fields - are Pulsed Fusion Drives.

I have never read of a drive which achieves velocities which can be achieved by the Pulsed Fusion Drive.

Like I said I am referring to Dyson because of his costs-issue only but I am sure if treaties and politics would have allowed the drive based on fusion bombs that concept would have been improved and developed further into the micro-explosion-concept impacting magnetic fields and further improvements would have been done and achieved up to now.

What Ulrich Walter says in his book simply means that the only usable fusion drive is the Pulsed Fusion Drive and it does have nothing to do with Inertial Concept or Magnetic Concept. Walter has nothing against one of the two. As far as he seems to prefer the Inertial Concept this has to do with the question how to make the pellets explode.

Two of the threads I mentioned Orion and Daedalus in were the threads to be avoided Orbital Mechanics and Disposal of radioactive materials into the sun. I would prefer if they wouldn't be revitalized!

Centrillium, you are right - the distracts should cease now. One question seems to be what a fusion drive would been when used for cislunar trips.

As far as I know New Horizons needed nine hours from here to the Moon - so it travels at a velocity of around 40,000 km/h driven chemically. As I understand it at least one of the fusion drives discussed might increase that velocity significantly.

This causes me the question if there is a maximum velocity which shouldn't be increased further. I suppose that the higher the cislunar velocity the harder the navigation and the process to enter a specific lunar orbit when coming from Earth and to enter a specific earthian orbit when coming from the moone.

Where is that maximum velocity? It will have to be compared to the velocity to be got by fusion drive and if the velocity got by the fusion drive is above that maximum then the fusion drive mustn't be used for cislunar trips, transportion etc.

What baout that?



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Last edited by Ekkehard Augustin on Sun Jan 22, 2006 4:26 pm, edited 1 time in total.



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Post    Posted on: Sun Jan 22, 2006 12:11 pm
spacecowboy wrote:
Chemical rockets might actually be *better* than fusion rockets (which would use a constant acceleration -- much much more efficient, but even less attractive from a travel agent's point of view).


The kind of fusion drives I'm talking about will produce only very slow accelerations. On board, the experience would essentially be one of microgravity - you might leave something floating in the air, and then when you return an hour later it'd have drifted up against the aft wall, but you'd have trouble actually seeing it fall unless you were very patient. :) The unit of acceleration for these fusion ships is likely to be the milligee.

Ekkehard Augustin wrote:
What baout that?


Hmm... I'm not sure. I don't really understand orbital mechanics well enough to say.

For Orion/pulsed fusion... I'm not really sure where you're coming from. If you aren't using nuclear explosives (Orion), then you have to use some sort of external means of igniting a fusion reaction in the fuel pellet, which is technically very difficult no matter what method you choose. The most developed approach in the real world is lasers, as used in the NIF. In that sense any pulsed fusion drive other than an Orion drive will either be based on ICF/lasers, or some approach (eg magnetised target fusion) which is even less developed in the real world, currently.

I agree that an Orion drive would be technically very straightforward compared to any other fusion drive concept, but I can't see it being used except in a dire emergency (this recalls Niven/Pournelle's novel 'Footfall', where humans build an Orion drive ship to fight off an alien invasion...). Assuming that Orion is not included as an option, I think that magnetic fusion is closer to realisation than inertial fusion.

Further, the advantages of external pulse propulsion lie in the fact that less mass needs to be invested in cooling systems for a given drive power since much of the energy simply escapes to space. This allows higher accelerations to be achieved. But for interstellar travel, exhaust velocity is the important characteristic rather than acceleration, and pulsed fusion has no particular advantage in that respect as far as I'm aware. So I think a continuously operating fusion drive could reach just as high a velocity as a pulsed fusion drive.

Yep, I've been drawn back to fusion... ah well. Its interesting anyways. :)


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Post    Posted on: Sun Jan 22, 2006 2:07 pm
sometimes it completely amazes me how much you know Ekkehard, you're like an enclyclopedia! :D
keep it up man! :P

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Post    Posted on: Sun Jan 22, 2006 4:23 pm
Hello, Rob,

I am very interested in God and the world and don't have a family. Most of what I know is linked to a lot of other things I knwo, experienced, learned, am able to do and the like - it's like a net.

If you keep up you own interest in things you easyly will know as much as I myself or even more when you are in my age - I am going to be 45 years old in a few months.

Hello, Centrillium,

Ulrich Walter says it would take around one year to achieve 0.12c by the Pulsed Fusion Drive. I remeber that Peter oppones to that issue but didn't list a link to his source for sme reasons I don't rember currently. But what's essential isn't the 0.12c but the difference in velocity to other drives.

The acceleration would be 1g. So within an hour the velocity would be a little bit less than 36 km/s compared to the 0.00981 km/s at the beginning. The 40,000 km/s of New Horizons is slow compared to that since it is 11.11 km/s only. And the would have to deceleration too this is the reason why i asked for the maximum velocity.



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Post    Posted on: Sun Jan 22, 2006 5:58 pm
Centrillium: it's amazing how quickly one can be drawn off-topic, isn't it? Trying to make a new thread at this point is of no use; the best bet is to just let 'er ride, and we'll get back to LTS architecture eventually (which I'm very interested in right now, by the way).

As for the milligee fusion drives, I admit my own confusion -- I thought you were talking about the mainline drives, the big 1g constant-accel kind (<grins> Me likes those...). In that case, Lunar transport systems (if the milligee drives are T/W- and fuel-efficient) could be very useful testbeds for Mars ships.

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Post    Posted on: Sun Jan 22, 2006 9:05 pm
"Yep, I've been drawn back to fusion... ah well. Its interesting anyways."

If you permit :-)

"every concept we've tried to push towards breakeven has been hard work, why would MTF be any easier?"

In the MTF based concept I mentioned, I can't remember the numbers but I remember being amused by the phenomenal beating the superconducting coils were expected to take, and reflecting on it I find it reminiscent of Orion in several ways. But it does seem kind of the right thing, even though there are other obvious problems and it's probably even harder than it looks - but it doesn't feel like a scheme that has many hidden impossibilities, mostly just the difficulties and limits you come to expect and which may be negotiable. MTF certainly requires some cooperation from nature, it isn't a sure-bet but it's plausible.

Almost every time you run into a problem during the process of optimization,(and most of rocket engineering involves it at some level) something like a material property which it turns out limits performance too much, and you change things quite radically so that you can avoid that one problem. So frequently it seems there's something fundamental about the difficulty which is at first hard to understand, and that although you don't realize it - because these things take time to see the interesting details. That again in optimization, the problem has come back, or something rather like it in this new system, just modified or abstracted a bit but often recognizable - a different nuance you maybe didn't manage to predict. Nature often puts up an almost unexpected struggle whenever we try to make the hard things easy, and if there were a few examples where that didn't prove to be true, we'd somehow manage to end up talking about the ones where it did.


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Post    Posted on: Sun Jan 22, 2006 9:40 pm
Quote:
What I wonder is - how is travel between Earth orbit and the moon, or Earth orbit and the Lagrange points, carried out?


How about this option, Earth to LEO via a simple rocket that is either reuseable or partly reuseable, ie SpaceX or EADSs Hopper etc. LEO to GTO and beyond via a Momentum eXchange Electrodynamic Reboost (MXER) Tether? The MXER idea is just the latest proposal in tethers a complete LEO to Luna surface transport system has been proposed. In fact the proposed Cislunar Tether Transport System, if used to transport mass back to LEO from the luna surface would hardly require any extra energy at all! Link to Paper


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Post    Posted on: Sun Jan 22, 2006 10:35 pm
Ekkehard Augustin wrote:
This causes me the question if there is a maximum velocity which shouldn't be increased further. I suppose that the higher the cislunar velocity the harder the navigation and the process to enter a specific lunar orbit when coming from Earth and to enter a specific earthian orbit when coming from the moone.

Where is that maximum velocity? It will have to be compared to the velocity to be got by fusion drive and if the velocity got by the fusion drive is above that maximum then the fusion drive mustn't be used for cislunar trips, transportion etc.

What baout that?

Dipl.-Volkswirt (bdvb) Augustin (Political Economist)
There is no absolute maximum velocity between Earth and the Moon, except possibly the speed of light. And going faster would make navigation easier, not harder, because gravity and motion of the Earth and Moon become less significant as you go faster and faster. It ultimately approaches a situation where you can just point your rocket where you want to go and start the engine.

Now there are many practical considerations that might make you want to go slower, but Ekkehard has never been one to let practical considerations interfere with his ideas.


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Post    Posted on: Sun Jan 22, 2006 10:49 pm
Here's something:

A wonderful paper describing a ship that nearly precisely matches my idea of a 2050s fusion-powered spacecraft.

Ekkehard, spacecowboy, it sounds like you both had much more futuristic things in mind. :) The problem with a fusion drive which can accelerate a ship at one gee... enough thrust to make one gee, a useful exhaust velocity, and you end up needing a reactor that develops megawatts for every kilogram of mass... which is way outside the scope of any fusion reactor we can reasonably expect to have for a long time to come.

Ekkehard, in particular - to make 0.12c, you need an exhaust velocity that's a meaningful percentage of c. Now a fusion drive might ultimately achieve that, but it'd need to be optimised pretty close to the theoretical limit. So - again, its a long way off!

nihiladrem - your insights on optimisation are very interesting... from my POV, I haven't been involved in engineering yet but I'm pretty sure its what I what to do eventually. nacnud - thanks very much for the links! I'll be sure to give those a read.


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Post    Posted on: Mon Jan 23, 2006 12:47 am
Wouldn't it be possible to simply (sure... "simply", he says) hook the fusion drive up to a fission reactor as an external power source? The fusion drive doesn't necessarily have to be self-sustaining...

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Post    Posted on: Mon Jan 23, 2006 8:29 am
Peter,

if you read my posts precisely and by word instead of interpreting me - one of your mistakes and errors on the list I have been speaking of to you - you will recognize that I didn't speak of an absolute maximum velocity between Earth and Moon.

What I am speaking about really is that the higher the velocity travelled by is the more deceleration will be required and the closer the distance to the object the journey is going to the less time to decelerate. This consequently means that each manoever has to be carried out more quickly, causing more stresses and requiring more precision and more advanced equipment, capabilities and the like.

This is a practice-argument.

Next, Peter, I am not talking about ideas but simply quoted Ulrich Walter because fusion drives had been mentioned before I did so. The arguments aren't mine but those of Ulrich Walter who is a physicist being a science astronaut. For this reason he can claim to be considered a serious source which to quote nobody can be blamed for - to try to do so, Peter, is another mistake of yours.

The main purpose of quoting Ulrich Walter was to avoid to much discussion about fusion drives here - but that obviously has failed not only but fueled that discussion. That's a pity - by the way: That has nothing to do with moderation.

To post more quotes from Ulrich Walter's book has nothing to do with argumentation pro or contra something but with completion and precision - to suspect a different meaning, Peter, is another mistake of yours and may have to do with your general tendency to interprete something. That tendency is a call to post more and more because to do so reduces your possibilities, opportunities and capacities to interprete - I am doing so as a poster simply.

As a non-physicist I am not willing and going to argue against Ulrich Walter who is a physicist. If others do so, then that's completely okay if they are physicists or engineers like Centrillium for example - but I myself as a non-physicists have to be very cautious to join someones standpoint.

At this point I think I should say something specific explicitly. I have been criticised because some posts of mine are considered to be psychological bad and it also has explicitly said that I don't like Psychologics to be applied - but interpreting another person or his/her posts is applying Psychologics and you, Peter, really do apply that nearly permanently. And that - to interprete that extremely is a concrete reason to consider the application of Psychologics to be a bad behaviour, a bad thing. This is one of the severe reasons of the very bad image Psychologics have to me and a lot of people I know here in and around Hamburg. There are a lot of ways to avoid to interprete others - these ways are very easy to go and all the lot people I mentioned know them and apply them.

As far as I listed some mistakes of your here, Peter, the list isn't complete. :x



But I don't want this to be discussed here - this would be a topic in the Off-Topic section. :?

So back again from Peter and Psychologics - :| what I know seems to mean that fusion drives shouldn't be applied for cislunar traffic. May be that inside the solar system the density of protons would allow for fusion ramjets but I don't remeber having read anything about their velocities and the difference to the velocity of the protons outside the solar system.

nacnud has mentioned the Cislunar Tether Transport System :!: . This might me much more practical and closer to practicability it looks to me.

So - :) sorry, Centrillium, I obviously have been misunderstanding. I am not out on 0.12c - cislunar. It would mean to go the distance from Earth to the Moon within less than 10 seconds. I meant it as an argument for doubting the application of fusion drives for cislunar trips only. Another argument is the theoretical and futuristice nature Pulsed Fusion Drives and other things Walter is talking about.

So - sorry again for the misunderstanding I caused you :| .



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