Potential torch drives

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Mr Anderson

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Nov 13, 2018, 4:03:04 PM11/13/18
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So what are, in your opinion, Best potential candidates for torch drives?

alie...@gmail.com

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Nov 21, 2018, 2:00:34 AM11/21/18
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On Tuesday, November 13, 2018 at 1:03:04 PM UTC-8, Mr Anderson wrote:
> So what are, in your opinion, Best potential candidates for torch drives?

Since you asked, a pulsed descendant of VASIMR. Yes, Impulse Drive.

It would use the VASIMR first stage, a medium-power induction heater to convert cold hydrogen (D-T mix; coulomb barrier 0.1 MeV, energy released 17.6 MeV) to plasma.

The plasma would then enter a low-frequency but very high power asymmetric microwave field that would pinch the plasma into small bundles, then squeeze the living crap out of them as they entered the reaction volume. The field would be just below the "arc across the waveguide" threshold so that with plasma within it will arc, using the current to heat the plasma the last little bit to fusion.

There would be a strong also asymmetric static background field to act as a "rocket bell" for thrust.

Pulse rate could be as low as a few dozen per second without noticeable lack of smoothness.

It will obviously need much more robust high-temperature superconducting magnets than we have now, and a very robust highly efficient heat-to-power recovery system to power itself as well as the crew's DVD players.

Don't ask me where we get the tritium.


Mark L. Fergerson

Mr Anderson

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Nov 22, 2018, 5:43:45 PM11/22/18
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It seems to me that this drive would need a really powerful power source, preferably something along the lines of thermonuclear reactor with MHD generator?
Where did you hear about this drive, can you give some sources on it? It looks like a top tier variation on standard VASIMR...
Also, I have a question to you specifically Mr. Fergerson, would you like to join a Discord server focused on hard science fiction topics? It was created by guy who runs ToughSF blog, and there are many great hard sf guys there! Asking because this place is pretty much dead

els.d...@gmail.com

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Nov 23, 2018, 2:27:30 PM11/23/18
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He isn't talking about a VASIMR drive at all. He is talking about magnetically comprising fusion fuel.

els.d...@gmail.com

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Nov 23, 2018, 2:31:23 PM11/23/18
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On Tuesday, November 13, 2018 at 3:03:04 PM UTC-6, Mr Anderson wrote:
> So what are, in your opinion, Best potential candidates for torch drives?

There aren't any. The cncept of a torch drive is fictional handwavium. You can have high delta-v or high thrust. Pick one. If you want your fusion drive to have high thrust, then you are going to have to crash its delta-v or it will overheat and melt.

alie...@gmail.com

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Nov 23, 2018, 11:38:14 PM11/23/18
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On Thursday, November 22, 2018 at 2:43:45 PM UTC-8, Mr Anderson wrote:
> It seems to me that this drive would need a really powerful power source,
> preferably something along the lines of thermonuclear reactor with MHD
> generator?

Yep. Any kind of "torch drive" will just to get it lit. If it produces
as much energy as we hope fusion will it could sustain itself while lit though.

> Where did you hear about this drive, can you give some sources on it?
> It looks like a top tier variation on standard VASIMR...

I basically made it up out of VASIMR, the Z-pinch machine and of course Star Trek impulse drive.

> Also, I have a question to you specifically Mr. Fergerson, would you like
> to join a Discord server focused on hard science fiction topics?

I'm not big on joining things- I had a hard enough time doing newsgroups but I'll look into Discord. Others have mentioned it.

> It was created by guy who runs ToughSF blog, and there are many great hard
> sf guys there! Asking because this place is pretty much dead

Yeah, it is. That's why I go into Quora.


Mark L. Fergerson

David Ellis

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Nov 24, 2018, 1:21:20 PM11/24/18
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Well, I wouldnt think that is entirely accurate. It is handwavium only in the sense that modern engineering doesn't understand how to make such a drive function without vaporizing itself.

To call it wholly a fictional concept isn't appropriate; physics does not prohibit such a device.

Torch drives are not impossible. They are simply difficult to design.

Yes, they are impossible with modern engineering, but in the context of science fiction, where one is looking into the possibilities of future engineering, they are certainly not beyond the realm of reason.

Mennolt van Alten

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Nov 26, 2018, 4:35:49 PM11/26/18
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On Tuesday, November 13, 2018 at 10:03:04 PM UTC+1, Mr Anderson wrote:
> So what are, in your opinion, Best potential candidates for torch drives?

The closest thing we could currently build IMO would be the Orion drive of course, which isn't very great on ISP but easily outpaces chemical drives while keeping the same levels of thrust.

eripe

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Nov 27, 2018, 4:36:30 AM11/27/18
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On Wednesday, November 14, 2018 at 4:03:04 AM UTC+7, Mr Anderson wrote:
> So what are, in your opinion, Best potential candidates for torch drives?

I think you are trying to build a golden gate bridge with nothing but wood: Its just not going be practical.

You need some breakthrough before it can happen, like the step from wood to steel.

200 Tesla magnets, Star Trek type force field, a microscopic wormhole to inside the sun, local modification of elemental force constants or inertia.

David Ellis

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Nov 27, 2018, 1:15:54 PM11/27/18
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You're correct about the magnets, but none of the other elements there are necessary for fusion-based drives. They are not mysteries in the realm of physics. The only barrier is one of engineering. In other words, one needs materials more resistant to high thermal and tensile stresses, fluids capable of managing extremely high thermal flux to effectively cool the components of a fusion rocket, and magnetic containment designs that are more efficient and more effective at preventing leakage of high-energy particles, as well as other things.

els.d...@gmail.com

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Nov 27, 2018, 3:03:12 PM11/27/18
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The reason that it is not possible is because of thermodynamics. The last time I checked, thermodynamics was a big part of physics.

On Tuesday, November 27, 2018 at 12:15:54 PM UTC-6, David Ellis wrote:
> You're correct about the magnets, but none of the other elements there are necessary for fusion-based drives. They are not mysteries in the realm of physics. The only barrier is one of engineering. In other words, one needs materials more resistant to high thermal and tensile stresses, fluids capable of managing extremely high thermal flux to effectively cool the components of a fusion rocket, and magnetic containment designs that are more efficient and more effective at preventing leakage of high-energy particles, as well as other things.

No, it is not just a matter of engineering. Materials made out of elements on the periodic table have certain thermodynamic limits based on underlying physical principles that aren't going away because you enter the word "future" in front of engineering. You are basically saying that if we get a bunch of magic materials then we can do magic things with them. The problem is that magic doesn't exist in real life.

Can you build a fusion drive? Yes, of course you can. Will it be a scifi torch drive? No, of course it will not.

Thomas Koenig

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Nov 27, 2018, 3:50:14 PM11/27/18
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Nuclear salt-water rockets might do. Don't try to take off in one,
though.

David Ellis

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Nov 28, 2018, 1:22:55 PM11/28/18
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Except that a torch drive is not a defined class of engines. It is an informal term. You're claiming that something is physically impossible when, aside from looking to demonstrate that such material properties are, in fact, impossible to achieve, you also literally don't know what it is you are saying cannot be done.

Also, materials are regularly engineered that possess properties far exceeding those of their constituent elements. Is there probably a limit that we will run into somewhere along the line? In many cases, probably. Do we know where the limits of thermal conductivity or other properties must be? No. We really don't.

Again, it IS simply a matter of mind-boggling engineering. It's not a matter of physical, universal constants.

winche...@gmail.com

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Dec 28, 2018, 10:53:12 AM12/28/18
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Agreed.
People were up in arms about using a nuclear pulse Orion drive for boosting payload from Earth's surface into orbit. Something about detonating hundreds of small nuclear bombs in the atmosphere alarmed them. ;)

Zubrin's infamous nuclear salt-water rocket is much worse, since it is a *continuously detonating* nuclear explosion drive.

But having said that, if you want a torch drive (defined as a rocket engine with both high specific impulse and high thrust) then Zubrin's NSWR is the closest thing we have to a theoretically possible engine. Even if many scientists say "Zubrin, I think you should be more explicit here in step two..."
http://www.projectrho.com/public_html/rocket/enginelist.php#nswr

els.d...@gmail.com

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Dec 28, 2018, 11:07:14 AM12/28/18
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I believe that you are missing the part where the properties in question are a result of electromagnetic interactions and are dependent ultimately on the physical constants that govern the electromagnetic force.

els.d...@gmail.com

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Dec 28, 2018, 11:09:03 AM12/28/18
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The fact that scientists don't take Zubrin's idea seriously, should be a giant red flag.

Thomas Koenig

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Dec 28, 2018, 12:25:56 PM12/28/18
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winche...@gmail.com <winche...@gmail.com> schrieb:

> People were up in arms about using a nuclear pulse Orion drive
> for boosting payload from Earth's surface into orbit. Something
> about detonating hundreds of small nuclear bombs in the atmosphere
> alarmed them. ;)

> Zubrin's infamous nuclear salt-water rocket is much worse,
> since it is a *continuously detonating* nuclear explosion drive.

Depends.

First, I don't hink anybody ever seriously considered using
Orion or a nuclear salt-water rocket close to Earth's atmosphere.

Otherwise, a continuous burn is far less destructive than a
sudden one - compare with what happens when a conventional
bomb explodes, compared to what happens if a solid rocket
booster burns.

els.d...@gmail.com

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Dec 28, 2018, 1:07:14 PM12/28/18
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The major problem with NSWR is how to keep the uranium from spontaneous uncontrolled nuclear detonation inside the vehicle. That is the step 2 that Mr. Chung alluded to in his post. This is a problem that to date, Zubrin can't actually solve.

David Ellis

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Dec 28, 2018, 1:29:38 PM12/28/18
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No, no, I understand where properties come from. What I'm saying is that you aren't alluding to any specific, known limits that make such torch drives, as a rule, physically impossible and not simply difficult to engineer. One cant demonstrate that an idea is truly ruled out by the laws of physics until one can actually make a theoretical calculation to that end.

"Torch drives" are not a specific group of engines, and thus offer no real information about parameters to consider. Without being able to compare some parameters to the properties of a system being designed, there is no determining, truly, whether or not that system can or cannot function.

In short, it's a moot point.

Thomas Koenig

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Dec 29, 2018, 12:01:02 PM12/29/18
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els.d...@gmail.com <els.d...@gmail.com> schrieb:
OK, this does sound like a potentially serious problem :-)

However, I'm not sure that this is something that can not
be handled. Using a boron- oder cadmium containing open-cell
structure (foam, or a lattice, or parallel pipes, or...)
should do the trick.

Plastics reinforced with boron fibers seem like a good
material at first glance.

els.d...@gmail.com

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Jan 4, 2019, 2:09:48 PM1/4/19
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The 2 percent aqueous solution of uranium tetrabromide is 38 percent uranium tetrabromide by mass. Uranium tetrabromide is over 5 times denser than water and since acceleration is equivalent to gravity, it should separate out of solution and collect at the back of the propellant tanks. We are talking about enough uranium to trigger a gigaton level explosion if it goes off.

Sure you can add enough mass to the system to fix most of the problems with this idea, but then you will not have torch drive performance. Plus Zubrin makes a pretty good whopper of an unproven assumption about controlling the reaction in the chamber. His assumption that he can limit the reaction to only happen where he wants by controlling the propellant velocity rests on the incorrect assumption that thermal neutrons only travel at their average velocity. When in fact there is a velocity distribution of fission neutrons and bunch of those neutrons will be traveling faster than the average. This could cause the continuously detonating fission reaction to move closer to the hull. You may not have enough time to even turn it off before the back of your spacecraft gets vaporized.

Simple mathematical models, which the NSWR is, do not mean that you have a workable solution. The best that you can do is to argue that it is a promising avenue of research that NASA should look into, but you shouldn't fool yourself into thinking that it is necessarily feasible. The fact that Zubrin can't convince anyone to fund either the testing of this idea or just engineering design work should be a giant red flag by itself.

Seriously, would you want to spend money that you were responsible for on a wild idea whose failure mode was to vaporize a multi-billion dollar spacecraft in the largest explosion in human history? Even if Zubrin is 95% right, a fuel pump malfunction could cause a multi-megaton or even gigaton explosion. And that is if you add machinery to continuously mix the solution to keep the uranium tetrabromide from collecting at the back of the propellant tanks.

For NASA, torch drive performance is not necessary. Torch drives don't get you there much faster than continuous acceleration in a sub-torch engine. Decreasing acceleration by a factor of 16, only increases maximum travel time by a factor of 4 if both engines accelerate continuously during the trip. Since the torch engine will most likely cut off early and coast, the travel time increase will actually be less than this.

On the whole this is a very risky idea with rather little payoff compared to alternatives.

In fact it is doubtful that even a space military would find low end torch drive performance useful.

Jaimie Vandenbergh

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Jan 4, 2019, 2:34:03 PM1/4/19
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On Fri, 4 Jan 2019 11:09:47 -0800 (PST), els.d...@gmail.com wrote:

>The 2 percent aqueous solution of uranium tetrabromide is 38 percent uranium tetrabromide by mass. Uranium tetrabromide is over 5 times denser than water

Yes, 5.19g/cm^3. This should have told you that a 2% aqueous solution of
UBr4 is about 10% UBr4 by mass, not 38%.

> and since acceleration is equivalent to gravity, it should separate out of solution

That's not how solutions work. You're thinking of suspensions. Solutions
do not separate under gravity.

Even if anything did precipitate and fall to the bottom, the turbulence
from pumping and acceleration/rotation etc would keep it pretty well
stirred. Not to mention that on any approach to critical mass (and
density) the heat would boil the aqeous and give it a real mix.

> and collect at the back of the propellant tanks. We are talking about enough uranium to trigger a gigaton level explosion if it goes off.

So, no. Your assumptions are well off so the problem isn't a problem in
reality. You're not going to have an accidental runaway.

Cheers - Jaimie
--
There are no normal people--only people you don't know very much about.
-- Nancy Lebovitz, rasfw

els.d...@gmail.com

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Jan 4, 2019, 2:44:36 PM1/4/19
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2 percent aqueous solution is 2 uranium tetrabromide (557.645 atomic mass units) molecules per 100 h20 (18 atomic mass units) molecules.

Since you can't do simple math, I'll ignore the rest of your post.

els.d...@gmail.com

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Jan 4, 2019, 2:58:59 PM1/4/19
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Actually no I won't. If the uranium tetrabromide precipitates and falls to the bottom then you build up a critical mass of uranium at the bottom. There is over 266 metric tons of uranium tetrabromide in these tanks. The dry mass of the spacecraft is only 300 metric tons.

els.d...@gmail.com

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Jan 4, 2019, 3:10:28 PM1/4/19
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Let's see:
98*18= 1764 amu
2*557.645= 1115.29 amu
1115.29/(1115.29+1764)=0.387348964501665
Multiply by 100 and you have 38.73%.
Why? Because 98+2=100.

Mike Van Pelt

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Jan 4, 2019, 3:33:28 PM1/4/19
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In article <0ocv2elif9qkn3tb0...@4ax.com>,
Jaimie Vandenbergh <jai...@sometimes.sessile.org> wrote:
>Even if anything did precipitate and fall to the bottom, the turbulence
>from pumping and acceleration/rotation etc would keep it pretty well
>stirred. Not to mention that on any approach to critical mass (and
>density) the heat would boil the aqeous and give it a real mix.

Plus, to get the Earth-Shattering Kaboom, it's not enough to
have a critical mass. You have to bring together a mass that is
critical on prompt neutrons alone *very very quickly* and keep
it together until a significant percentage of the fissionable
material fissions. Otherwise, you get a fizzle.

(See: Hiroshima "gun" design, Nagasaki "implosion" design.)

--
Mike Van Pelt | "I don't advise it unless you're nuts."
mvp at calweb.com | -- Ray Wilkinson, after riding out Hurricane
KE6BVH | Ike on Surfside Beach in Galveston

Jaimie Vandenbergh

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Jan 4, 2019, 3:47:34 PM1/4/19
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On Fri, 4 Jan 2019 11:44:34 -0800 (PST), els.d...@gmail.com wrote:

>2 percent aqueous solution is 2 uranium tetrabromide (557.645 atomic mass units) molecules per 100 h20 (18 atomic mass units) molecules.

You are free to do a Humpty Dumpty and use existing words to mean whever
you like, but if you wish to communicate - or base your calculations on
something defined in the usual manner - then you probably shouldn't.

This is a highly unorthodox usage of "percent solution".

>Since you can't do simple math, I'll ignore the rest of your post.

Feel free. I hear it is bliss.

Cheers - Jaimie
--
I always wanted to be someone. I should have been more specific.
-- Lily Tomlin

els

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Feb 15, 2019, 8:28:23 PM2/15/19
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On Friday, January 4, 2019 at 2:47:34 PM UTC-6, Jaimie Vandenbergh wrote:
Maybe you should try reading Zubrin's paper: http://path-2.narod.ru/design/base_e/nswr.pdf

Because Zubrin states in the 2nd paragraph that his solution is 2 atoms of uranium per 100 molecules of water. He apparently had the same chemistry textbook as I did.

Jaimie Vandenbergh

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Feb 15, 2019, 9:42:26 PM2/15/19
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On Fri, 15 Feb 2019 17:28:22 -0800 (PST), els <els.d...@gmail.com>
wrote:
How closely did you read it?

*He* knows that it's so uncommon that he needs to specify this usage in
the paper:

"Assuming a solution of 2 atoms of 20% enriched uranium per 100
molecules of water"

"a solution of 2% by number uranium bromide salt solution in water".

Zubrin has also done the math and spells it out in the paper - "In the
mission described, the NSWR used 83.6 tonnes of aqueous propellant (41.8
for each of TSI and EOI), 16.7 tonnes out which is uranium. Of this
uranium, 3.34 tonnes are actually fissile U235."

You said "38% uranium tetrabromide by mass" which is correct in a 2% by
number solution, but vitally ignores the fissile vs inert isotope ratio.
Again, clearly stated in the paper.

He's also aware - unlike you - that a salt solution doesn't "separate
out and collect at the back of propellant tanks". The design wouldn't
work at all without a very even mix of liquid fuel. Any 'runaway'
reaction would at worst burst the plenum chamber, causing the fission
reaction to sputter out immediately.

Your point was "We are talking about enough uranium to trigger a gigaton
level explosion if it goes off", but even with the 2% by count solution
this is still nonsense.

This nuclear fuel fluid doesn't act like normal hypergolic rocket fuel,
there's no way to get an uncontrolled burn. Getting a burn at all is
very, very hard.

.... wow, that was a waste of fifteen minutes. I don't know why I
bothered.

Cheers - Jaimie
--
"Prediction is very difficult, especially about the future"
- Niels Bohr

kiran patel

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Dec 3, 2020, 6:23:58 AM12/3/20
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jack tingle

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Nov 18, 2021, 11:47:59 AM11/18/21
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On Thursday, December 3, 2020 at 6:23:58 AM UTC-5, kiran patel wrote:
> On Wednesday, 14 November 2018 at 02:33:04 UTC+5:30, adam.w.k...@gmail.com wrote:
> > So what are, in your opinion, Best potential candidates for torch drives?
The original concept was direct conversion of some fraction of the baryonic reaction mass to energy, and the resulting stew of particles expelled at exceptionally high speed. It allowed ocean landings and takeoffs plus fast solar system travel.

That can't happen, because nuclear physics. The modern equivalent is probably a NERVA type fission engine, or an Orion.

If we ever get compact, high-heat-rate fusion reactors with very high charge density, maybe a fusion drive.

Unless you are Jack Williamson, in which case you can mine the Asteroid Belt for anti-matter. :)
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