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 Ferris
PsychedelicJourneyman
  
Registered: 03/12/06
Posts: 6,954
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 Fusion Scramjets in Space
#8597594 - 07/05/08 02:29 PM (4 months, 28 days ago) |
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No, they haven't been invented. I was just thinking earlier and the idea occurred to me of using either interstellar matter or the high energy plasma ejected from the sun as fuel for a theoretical future spaceship with a fusion reactor as an engine.
Particle physicists, rocket scientists, smart people in general, help me debunk this idea. Shoot as many holes in it as you can think of. Feel free to patch em up though if you can by stipulating an assumption of some sort though.
A couple problems I thought of right away:
First, fusion reactors are really large as of this point in time, so it would be very difficult to get one into space. So the spaceship would need to either
1. Much smaller and lifted into space by a large conventional rocket (a smaller size is probably necesarry to make it feasible in other ways too)
2. Lifted into space in pieces, preferably by a space elevator
3. Be modifiable so that it can work in space and as a planetary fusion scramjet (which probably poses its own unique problems). This might be done with movable parts, or with just a stage system.
Ok, second, I'm not even sure if particles in space are appropriate for our fusion technologies as fuel. I'm pretty sure I've heard of hydrogen being used, so this might be a relatively minor issue.
Third, if the ship were to use the solar wind (plasma ejections) as it's primary fuel (since I beleive it's more abundant than interstellar matter inside the solar sytem), the ship may have to be able to first reach the speed of these particles before the scramjet could work, which at a couple hundred kilometers per second is about ten times faster than our fastest spaceship has acheived. A novel solution to this may be to first let the ship "catch" the particles coming at it, let it use that to approach the speed of them, then use a small onboard fuel package to push it over that limit, then reverse the direction of the scoop so that it's catching the particles that it is overtaking. Complicated, huh.
Fourth, depending on the particle density in space, the scoop may have to be very large. I suppose such a calculation would involve finding the amount of energy released by the sun over a certain amount of time and comparing that with the distance to determine how many particles are at that distance. I could probably manage that much, but it's not really necesarry because at this point we don't know how much fuel our theoretical fusion reactor even needs. If anyone could hazard some sort of guess, that would help immensly in possibly debunking this idea.
Fifth, this may only work inside the termination shock of the solar system if dependant on solar wind. Hopefully at this point however, it has reached a desired speed. By the way, Voyager 2 became the second vehicle to pass this point recently and was the first to collect data on it. Cool stuff. As a totally seperate idea, I wonder if it's possible to harness a shock wave of that nature to gain speed. I beleive it's partially electromagnetic in nature, so this may be possible, I don't know.
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The life of American Vagabonds
To live is the rarest thing in the world. Most people exist, that is all.
-Oscar Wilde
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 zouden
Neuroscientist
Registered: 11/12/07
Posts: 3,341
Loc: Australia
Last seen: 14 hours, 50 minutes
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 Re: Fusion Scramjets in Space [Re: Ferris]
#8599194 - 07/05/08 11:38 PM (4 months, 28 days ago) |
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Didn't you just describe the Bussard Ramjet?
http://en.wikipedia.org/wiki/Bussard_ramjet
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Wave upon wave of demented avengers
Marched cheerfully out of obscurity into the dream
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Ferris
PsychedelicJourneyman
Registered: 03/12/06
Posts: 6,954
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Re: Fusion Scramjets in Space [Re: zouden]
#8599206 - 07/05/08 11:42 PM (4 months, 28 days ago) |
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You're a couple hours late pointing that out to me:
http://www.newmars.com/forums/viewtopic.php?f=5&t=6131
I'm surprised you knew about that though.
I'll just add this to the list of semi-obvious shit that I independently invented. I am glad that I got a couple of the basic ideas down though before finding that wiki. At least it's not just another crackpot theory (although some would say it is).
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The life of American Vagabonds
To live is the rarest thing in the world. Most people exist, that is all.
-Oscar Wilde
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zouden
Neuroscientist
Registered: 11/12/07
Posts: 3,341
Loc: Australia
Last seen: 14 hours, 50 minutes
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Re: Fusion Scramjets in Space [Re: Ferris]
#8599219 - 07/05/08 11:47 PM (4 months, 28 days ago) |
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Yeah I've known about them since I read Ringworld as a kid 
That's impressive that you figured it out on your own though! Next you'll say "hey guys I came up with the idea of a working fusor!" and you can continue the (very important) work of the late George Bussard.
http://en.wikipedia.org/wiki/Polywell
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Wave upon wave of demented avengers
Marched cheerfully out of obscurity into the dream
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Ferris
PsychedelicJourneyman
Registered: 03/12/06
Posts: 6,954
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Re: Fusion Scramjets in Space [Re: zouden]
#8599231 - 07/05/08 11:51 PM (4 months, 28 days ago) |
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I'm going to have to drink more caffeine before I can understand that article. I spent most of the day hammering out the details of something that's already been thought up. At least I learned quite a bit about rocket science and fusion in the meantime 
Niven's works are near the top of my list of scifi to read. I've read just about every other major scifi writer out there at this point. Somewhere in the range of 100 books in the last few years.
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The life of American Vagabonds
To live is the rarest thing in the world. Most people exist, that is all.
-Oscar Wilde
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Ferris
PsychedelicJourneyman
Registered: 03/12/06
Posts: 6,954
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Re: Fusion Scramjets in Space [Re: Ferris]
#8599273 - 07/06/08 12:10 AM (4 months, 28 days ago) |
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Any comments on using the termination shock to gain speed, like they use planets for their slingshot effect, but different?
--------------------
The life of American Vagabonds
To live is the rarest thing in the world. Most people exist, that is all.
-Oscar Wilde
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zouden
Neuroscientist
Registered: 11/12/07
Posts: 3,341
Loc: Australia
Last seen: 14 hours, 50 minutes
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Re: Fusion Scramjets in Space [Re: Ferris]
#8599393 - 07/06/08 01:01 AM (4 months, 28 days ago) |
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You're way ahead of me on this.
Is it possible to gain energy from the sonic boom when a plane breaks the sound barrier?
--------------------
Wave upon wave of demented avengers
Marched cheerfully out of obscurity into the dream
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Ferris
PsychedelicJourneyman
Registered: 03/12/06
Posts: 6,954
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Re: Fusion Scramjets in Space [Re: zouden]
#8599496 - 07/06/08 01:30 AM (4 months, 28 days ago) |
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Hm, well, not in any way that I can think of. But with what we're talking about here, we have two supersonic forces colliding, the termination shock (solar winds) and the bow shock (interstellar winds). The area where the pressure balance between the two is called the heliopause. Actually this area may be the ideal candidate for whatever I have in mind, although the area of higher energy (the termination shock) just jumped out at me first (probably due to the whole voyager deal).
It just seems to me that where you have two forces colliding, producing energy and as-yet-not-understood electromagnetic forces, that there is potential for harvesting a "natural resource". Perhaps the most that could be gained is the combination of the two combined energies. So say, a solar wind vehicle that is traveling at it's max speed of a couple hundred km/s (the average speed of solar wind), that it can boost another hundred km/s, thereby reducing travel time by 50%.
I'll try to think of something more concrete as to methodology. I know there's something in there. The truth is it might be useless to discuss this until voyager hits the heliosphere in another couple of years.
--------------------
The life of American Vagabonds
To live is the rarest thing in the world. Most people exist, that is all.
-Oscar Wilde
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zouden
Neuroscientist
Registered: 11/12/07
Posts: 3,341
Loc: Australia
Last seen: 14 hours, 50 minutes
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Re: Fusion Scramjets in Space [Re: Ferris]
#8599535 - 07/06/08 01:43 AM (4 months, 28 days ago) |
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I wonder if a combination of a solar sail and a Bussard ramjet would provide a good zero-fuel propulsion system for interstellar travel.
Of course, even with the very best propulsion you are still limited by the speed of light which puts most destinations out of the range of a human lifetime so we have all kinds of problems.
You might be interested in this: it's a serious attempt at building a superluminal 'warp drive'. Last I heard, they were constructing a device (a large rotating magnet in space) which will tell them if the underlying theory is correct, in which case it's possible that a warp drive could work. I find it exciting to know that physicists are working on this sort of thing...
http://www.newscientist.com/channel/fundamentals/mg18925331.200.html
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Wave upon wave of demented avengers
Marched cheerfully out of obscurity into the dream
|
Ferris
PsychedelicJourneyman
Registered: 03/12/06
Posts: 6,954
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Re: Fusion Scramjets in Space [Re: zouden]
#8599564 - 07/06/08 02:00 AM (4 months, 28 days ago) |
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If the sail were an electromagnetic feild like in the m2p2 solar wind vehicle, then I suppose the feild could function as both a scoop for hydrogen and a sail (since apparently the scoop needed to get enough fuel for a sustainable reaction is a little larger than I had hoped for, at least according to the wiki article; and therefore can't be made solid. I assume this is for the same reasons that we can't build a pure dyson sphere. Gravity and all that).
However, we have advanced in science a bit since the 60s. So if the electromagnetic scoop idea doesn't pan out, perhaps using the higher energy particles in solar wind would be a good idea, specifically protons and depleted boron ions to create p/b11 fusion. Because of the higher energy and increased matter density of these particles in the inner regions of the solar system, it would cost less matter to build a sustainable reaction, and the necesary size of the scoop would be smaller and possibly solid.
The downside to this is that the reaction would probably die out during interstellar travel and have to be restarted inside another star system. Since we're already assuming that we've made fusion reactors smaller, it probably wouldn't be too far fetched to add in both a p/b11 fusion reactor and a hydrogen reactor. It may be near-doubling the mass, but it may be either worth it, or necesary.
--------------------
The life of American Vagabonds
To live is the rarest thing in the world. Most people exist, that is all.
-Oscar Wilde
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