Fusion with space related aspects thread

[LMT]

In Daedalus, that is really derived from another Winterberg design, the heat was radiated away by the large engine bell.  The bell operating temperature (safely under the melting point) fixed the bell size.  The text does seem to propose that the engine bell is cooled by the injected propellant.

Daedalus had ~ 100x the mass of the notional tug + Starship system, and ~ 1000x the delta-v.  And that design is 4 decades older than Winterberg 2015, where just 10 kg of LH2 removes a heat flux far greater than a tug's. 

Why defer to Daedalus?

[lamontagne]

In Daedalus, that is really derived from another Winterberg design, the heat was radiated away by the large engine bell.  The bell operating temperature (safely under the melting point) fixed the bell size.  The text does seem to propose that the engine bell is cooled by the injected propellant.

Daedalus had ~ 100x the mass of the notional tug + Starship system, and ~ 1000x the delta-v.  And that design is 4 decades older than Winterberg 2015, where just 10 kg of LH2 removes a heat flux far greater than a tug's. 

Why defer to Daedalus?

Because they did their calculations and wrote them up in a readable paper?  And physics has remained the same for the last 40 years, AFAIK.
From Winterberg 2015, my understanding is that the power of the explosion is 1e18 erg. or 100 GJ.
10% would be 1e17 ergs, or 10 GJ. 
The specific heat of hydrogen is 14 kJ/kgC, so 10 kG 140 kJ/C.  10 Gj / 14 kJ is 714 000 °C.  That's a bit too hot, so propellant cooling seems out?

The Daedalus first stage engine bell radiated 7 GW of induction heating and was 100m in diameter, so just about right.  you could likely boost it to 10 GJ without melting. But a bit big for the design?

You were saying?

[LMT]

physics has remained the same for the last 40 years, AFAIK.

Weird text, though.  If you want to argue with the fusion physicist, and flag his recent 10 kg number as very false, you'll have to make a point; i.e., quote and correct him line-by-line.

[lamontagne]

physics has remained the same for the last 40 years, AFAIK.

Weird text, though.  If you want to argue with the fusion physicist, and flag his recent 10 kg number as very false, you'll have to make a point; i.e., quote and correct him line-by-line.

I did exactly that, that's why there are numbers in the post.  Not my fault he didn't calculate the specific heat and the temperature gain for his 10% eddy currents.  Of course I may be wrong, but your refutation of my refutation is more of an ad hominem attack that an actual useful comment, and an out of context citation of a little joke, adding to the weakness of the intervention. 
Anyway, I wasn't really talking to you, I was just trying to be nice to Interestedengineer.

[LMT]

Weird text, though.  If you want to argue with the fusion physicist, and flag his recent 10 kg number as very false, you'll have to make a point; i.e., quote and correct him line-by-line.

I did exactly that, that's why there are numbers in the post.  Not my fault he didn't calculate the specific heat and the temperature gain for his 10% eddy currents.  Of course I may be wrong, but your refutation of my refutation is more of an ad hominem attack that an actual useful comment, and an out of context citation of a little joke, adding to the weakness of the intervention. 
Anyway, I wasn't really talking to you, I was just trying to be nice to Interestedengineer.

No, if you think the physicist got it wrong, say so, and clearly.  If 10 kg is the wrong number, calculate the right number.  Make your point.  And for Pete's sake, quote the published text at issue; it was four decades post-Daedalus, after all.

[Twark_Main]

Weird text, though.  If you want to argue with the fusion physicist, and flag his recent 10 kg number as very false, you'll have to make a point; i.e., quote and correct him line-by-line.

I did exactly that, that's why there are numbers in the post.  Not my fault he didn't calculate the specific heat and the temperature gain for his 10% eddy currents.  Of course I may be wrong, but your refutation of my refutation is more of an ad hominem attack that an actual useful comment, and an out of context citation of a little joke, adding to the weakness of the intervention. 
Anyway, I wasn't really talking to you, I was just trying to be nice to Interestedengineer.

No, if you think the physicist got it wrong, say so, and clearly.

They did.

  If 10 kg is the wrong number, calculate the right number.

That, of course, is entirely unnecessary extra work.  Their point is only to show that the given numbers don't work, and they amply showed that.


Now stop being a pest. 

[lamontagne]

Weird text, though.  If you want to argue with the fusion physicist, and flag his recent 10 kg number as very false, you'll have to make a point; i.e., quote and correct him line-by-line.

I did exactly that, that's why there are numbers in the post.  Not my fault he didn't calculate the specific heat and the temperature gain for his 10% eddy currents.  Of course I may be wrong, but your refutation of my refutation is more of an ad hominem attack that an actual useful comment, and an out of context citation of a little joke, adding to the weakness of the intervention. 
Anyway, I wasn't really talking to you, I was just trying to be nice to Interestedengineer.

No, if you think the physicist got it wrong, say so, and clearly.  If 10 kg is the wrong number, calculate the right number.  Make your point.  And for Pete's sake, quote the published text at issue; it was four decades post-Daedalus, after all.

It was quoted verbatim by Interestedengineer in his post.  That's what started this, I hardly need to repeat it.  I have the actual paper in reference, I find links to old posts annoying.  Regarding Daedalus, it's not because it is old that it is not relevant.  Einstein wrote his paper of E=mc2 about 100 years ago and no one is saying it's out of date.

I can't be clearer then the math I used.  It's absurdly simple.  Specific heat x mass flow x temperature difference = Power

I cannot calculate a correct number, the concept is fundamentally flawed, based on the numbers in the paper.  Perhaps it's a typo, and Winterberg meant to write 0,01% eddy current heating.  That type of mistake happens fairly often.

[LMT]

No, if you think the physicist got it wrong, say so, and clearly.  If 10 kg is the wrong number, calculate the right number.  Make your point.  And for Pete's sake, quote the published text at issue; it was four decades post-Daedalus, after all.

It was quoted verbatim by Interestedengineer in his post.  That's what started this, I hardly need to repeat it.  I have the actual paper in reference, I find links to old posts annoying.  Regarding Daedalus, it's not because it is old that it is not relevant.  Einstein wrote his paper of E=mc2 about 100 years ago and no one is saying it's out of date.

I can't be clearer then the math I used.  It's absurdly simple.  Specific heat x mass flow x temperature difference = Power

You refuse to give a corrected coolant mass number because you don't know how to calculate it. 

Of course I may be wrong...

If you never venture a number, you'll never be right.

[lamontagne]

No, if you think the physicist got it wrong, say so, and clearly.  If 10 kg is the wrong number, calculate the right number.  Make your point.  And for Pete's sake, quote the published text at issue; it was four decades post-Daedalus, after all.

It was quoted verbatim by Interestedengineer in his post.  That's what started this, I hardly need to repeat it.  I have the actual paper in reference, I find links to old posts annoying.  Regarding Daedalus, it's not because it is old that it is not relevant.  Einstein wrote his paper of E=mc2 about 100 years ago and no one is saying it's out of date.

I can't be clearer then the math I used.  It's absurdly simple.  Specific heat x mass flow x temperature difference = Power

You refuse to give a corrected coolant mass number because you don't know how to calculate it. 

Of course I may be wrong...

If you never venture a number, you'll never be right.

The correct equation is literally spelled out one line above your reply. 10 GW / 14 000 j/kg°K / 1000°K = 714 kg/s.
10e18 erg is 100 GJ, 10% of that is 10 GJ.  1 hz takes one second so that 10 GW of power.

[LMT]

10 GW / 14 000 j/kg°K / 1000°K = 714 kg/s.
10e18 erg is 100 GJ, 10% of that is 10 GJ.  1 hz takes one second so that 10 GW of power.

It's absurdly simple.  Specific heat x mass flow x temperature difference = Power

I cannot calculate a correct number, the concept is fundamentally flawed, based on the numbers in the paper.  Perhaps it's a typo, and Winterberg meant to write 0,01% eddy current heating.  That type of mistake happens fairly often.

So which is it?

- coolant mass is off by a huge factor?

- eddy current heating is off by a huge factor?

- it's an incalculable mystery due to unspecified flaw(s)?

It's emotional, sure.  But understand:  his hydrogen and boron capture heat from neutrons, and the magnetic mirror reflects the plasma, all to keep hot particles away from the metal reflector.  Think about how that must limit blast heat transfer mechanisms.

[LMT]

Cross-post:  Optimizing a Fusion Tug -- Tritium Self-Sufficiency from Thermal Neutrons

[LMT]

Cross-post:  Tritium Self-Sufficiency from Depleted Uranium

Economical sourcing of fusion fuel can be a challenge in some schemes.  Achieving tritium self-sufficiency from "waste" thermal neutrons, via inexpensive depleted uranium and 6Li, would seem to be a significant efficiency.  Cross-post ref Fig. 3-4 indicates that a fission-fusion hybrid system can breed up to ~ 1.4x the tritium consumed, using only 238U thermal neutrons.  Possibly a Winterberg 3F system, offering additional 235U thermal neutrons, could breed even more. 

At $30,000 per gram, excess tritium might even pay for the 238U and 235U consumed.  Couple that to a methalox ISRU infrastructure, and the sourcing of 3F nuclear fuel and chemical high explosive could be more economical than, say, fueling a 3He fusion tug.  (What is the most economical method for producing 3He at fleet scale today?)

And as we saw, 3F DT fusion gives a specific energy that seems very hard to surpass without antimatter. 

-

Now that 3F DT explosions below 100 t TNT equivalent seem feasible and economical, what alternate nuclear designs can offer competitive tug systems?  Perhaps PuFF (Adams et al. 2020)?  Note that PuFF engineering targets propulsion for "one month to Mars", opposite many recent forum pronouncements.

How to gauge current TRL of various PuFF subsystems?

Refs.

Adams, R.B., Allen, M., Demonceaux, A., Doughty, G., Giddens, P., Gonzalez, K., Kuczek, J., Lloyd, K., Williams, R., Cassibry, J. and Schilling, N., 2020. The pulsed fission-fusion (Puff) engine: Development status (No. AIAA-2020-4082).

[LMT]

Are posters struggling with fusion system comparisons? 

Elmar?

-

But looking more closely at PuFF in Taylor et al. 2020, we see why PuFF engine TRL must be low today.  Instability is expected in the dynamic PuFF ignition process -- e.g., disturbances in the laminar lithium streams of Adams et al. 2020 -- and the researchers acknowledge the challenges:

Dynamic effects and phenomena such as the Rayleigh-Taylor Instability will
play an important role in the implosion and burn of these hybrid fuels. These
along with two and three dimensional effects are planned to be studied as a
part of the PuFF program in more robust modeling efforts.

Cf. Winterberg 2004, re Rayleigh-Taylor instability in a 3F device:

Theoretical and experimental studies made with capsules imploded by the Nova
laser showed sufficient stability for convergence ratios...  [R]atios are within the
limit of feasibility against Rayleigh-Taylor instability growth...  There can be no
doubt that high explosives can be made sufficiently uniform and homogenous to
reach the same implosion symmetry as with lasers.

To that end, ISRU MOX, being a product of miscible cryogenics, would be inherently homogenous.  A spherical MOX shell would be robustly uniform and symmetric.  Therefore, Rayleigh-Taylor instability shouldn't be an issue for a 3F MOX device.

Beyond that, a PuFF tug would likely mass 10-100x a 3F Starship tug, with its immense lithium tank, Z-pinch pulser assembly, nuclear power plant, multiple radiators, etc.  See example masses in Adams et al. 2014.  The rocket equation doesn't like an extremely massive tug.

Can PuFF be competitive as a fleet tug system, or is it inherently unfit for purpose?

Refs.

Adams, R.B., Allen, M., Demonceaux, A., Doughty, G., Giddens, P., Gonzalez, K., Kuczek, J., Lloyd, K., Williams, R., Cassibry, J. and Schilling, N., 2020. The pulsed fission-fusion (Puff) engine: Development status (No. AIAA-2020-4082).

Adams, R.B., Cassibry, J.T. and Schillo, K., 2014. Developing the pulsed fission-fusion (PuFF) engine. In 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference (p. 3520).

Taylor, B., Cassibry, J. and Adams, R., 2020. Ignition and burn in a hybrid nuclear fuel for a pulsed rocket engine. Acta Astronautica, 175, pp.465-475.

Winterberg, F., 2004. Mini fission-fusion-fission explosions (mini-nukes). A third way towards the controlled release of nuclear energy by fission and fusion. Zeitschrift für Naturforschung A, 59(6), pp.325-336.

[LMT]

10 GW / 14 000 j/kg°K / 1000°K = 714 kg/s.
10e18 erg is 100 GJ, 10% of that is 10 GJ.  1 hz takes one second so that 10 GW of power.

It's absurdly simple.  Specific heat x mass flow x temperature difference = Power

I cannot calculate a correct number, the concept is fundamentally flawed, based on the numbers in the paper.  Perhaps it's a typo, and Winterberg meant to write 0,01% eddy current heating.  That type of mistake happens fairly often.

So which is it?

- coolant mass is off by a huge factor?

- eddy current heating is off by a huge factor?

- it's an incalculable mystery due to unspecified flaw(s)?

It's emotional, sure.  But understand:  his hydrogen and boron capture heat from neutrons, and the magnetic mirror reflects the plasma, all to keep hot particles away from the metal reflector.  Think about how that must limit blast heat transfer mechanisms.

Lamontagne found no clarification.  Well, it's just his misreading.   

A fusion drive couldn't have good performance if it expelled Lamontagne's 714 kg of LH2 coolant for every 100 kg of LH2 fusion propellant.  His immense coolant tanks aren't found in Winterberg 2015, etc. -- nor in his preferred Project Daedalus.  Daedalus delta-v requires all 2H/3He be consumed as fusion propellant, only, per the rocket equation.

To analyze energy flow, you might start with a previous post.  Try each interaction in turn:  e.g., estimate induced forces and currents between elements (1.) and (3.), with the Lorentz Force law, etc.

[lamontagne]

10 GW / 14 000 j/kg°K / 1000°K = 714 kg/s.
10e18 erg is 100 GJ, 10% of that is 10 GJ.  1 hz takes one second so that 10 GW of power.

It's absurdly simple.  Specific heat x mass flow x temperature difference = Power

I cannot calculate a correct number, the concept is fundamentally flawed, based on the numbers in the paper.  Perhaps it's a typo, and Winterberg meant to write 0,01% eddy current heating.  That type of mistake happens fairly often.

So which is it?

- coolant mass is off by a huge factor?

- eddy current heating is off by a huge factor?

- it's an incalculable mystery due to unspecified flaw(s)?

It's emotional, sure.  But understand:  his hydrogen and boron capture heat from neutrons, and the magnetic mirror reflects the plasma, all to keep hot particles away from the metal reflector.  Think about how that must limit blast heat transfer mechanisms.

Lamontagne found no clarification.  Well, it's just his misreading.   

A fusion drive couldn't have good performance if it expelled Lamontagne's 714 kg of LH2 coolant for every 100 kg of LH2 fusion propellant.  His immense coolant tanks aren't found in Winterberg 2015, etc. -- nor in his preferred Project Daedalus.  Daedalus Isp requires all 2H/3He be consumed as fusion propellant, only, per the rocket equation.

To analyze energy flow, you might start with a [ Try each interaction in turn:  e.g., estimate induced forces and currents between elements (1.) and (3.), with the Lorentz Force law, etc.

What cooling tanks?  I have no cooling tanks,I don't even have a design!  Winterberg has a design, we're quoting Winterberg, not me.  And Winterberg's hypothesis do not work, at least as far as cooling goes.

''Cooling the metallic reflector can be done with liquid hydrogen becoming part of the exhaust, as in chemical liquid fuel rocket technology. This is unlikely to amount to more than 10% of the liquid hydrogen heated by the neutrons of the
fusion explosion.''
Why is it unlikely?  Winterberg doesn't say.

What can you possibly have missed in my explanation?
Winterberg proposes a flow of 0,1 tonnes per second.  It's writen in his text.
He then proposes that the eddy curents can hardly be more than 10% of the fireball, that is 1e18 erg1, so 1 e17 ergs. or 10 GW.

Since the hydrogen is already a gas, we can only use it as a heat transfer fuel, where it has the excellent specific heat of 14 000 kJ/kg K. 
Q=m*cp*dt so dt = 10 000 000 000 / 10 / 14 000 = 71 400 Kelvin.  This is impossible to contain in a nozzle, since nothing can survice that temperature.

So the hypothesis of Winterberg are wrong.  10 kg of hydrogen cannot in any way cool 10% of the fireball.  So either the engine does not work, or the 10% hypothesis is wrong, or both.  For the engine to be correct, we need the eddy currents to be about 100 times lower, so rather than 10% they need to be 0,1%.
I don't need to prove this, Winterberg, or anyone who want to use his engine does.  As far as I'm converned, it doesn't work, since his design fails at one of the most basic thermodynamic equation that exists.

I cannot guess what Winterberg wanted to say.  Perhaps he does think it is 0,1% and his spell checker failed.  I'm not going to ask him.  But I would appreciate that you do not give the error to me, and attribute to me an unworkable design that you pull out of thin air. 

[LMT]

What cooling tanks?  I have no cooling tanks,I don't even have a design!  Winterberg has a design, we're quoting Winterberg, not me.  And Winterberg's hypothesis do not work, at least as far as cooling goes.

''Cooling the metallic reflector can be done with liquid hydrogen becoming part of the exhaust, as in chemical liquid fuel rocket technology. This is unlikely to amount to more than 10% of the liquid hydrogen heated by the neutrons of the
fusion explosion.''
Why is it unlikely?  Winterberg doesn't say.

What can you possibly have missed in my explanation?
Winterberg proposes a flow of 0,1 tonnes per second.  It's writen in his text.
He then proposes that the eddy curents can hardly be more than 10% of the fireball, that is 1e18 erg1, so 1 e17 ergs. or 10 GW.

Since the hydrogen is already a gas, we can only use it as a heat transfer fuel, where it has the excellent specific heat of 14 000 kJ/kg K. 
Q=m*cp*dt so dt = 10 000 000 000 / 10 / 14 000 = 71 400 Kelvin.  This is impossible to contain in a nozzle, since nothing can survice that temperature.

So the hypothesis of Winterberg are wrong.  10 kg of hydrogen cannot in any way cool 10% of the fireball.  So either the engine does not work, or the 10% hypothesis is wrong, or both.  For the engine to be correct, we need the eddy currents to be about 100 times lower, so rather than 10% they need to be 0,1%.
I don't need to prove this, Winterberg, or anyone who want to use his engine does.  As far as I'm converned, it doesn't work, since his design fails at one of the most basic thermodynamic equation that exists.

I cannot guess what Winterberg wanted to say.  Perhaps he does think it is 0,1% and his spell checker failed.  I'm not going to ask him.  But I would appreciate that you do not give the error to me, and attribute to me an unworkable design that you pull out of thin air.

?

No, Winterberg 2015, like Daedalus, uses a Winterberg magnetic mirror nozzle to limit heat transfer.  Same basic thermodynamics, etc.

You've talked a lot about Daedalus, and you saw no thermodynamics problem there.  So you really should have recognized the plain Winterberg 2015 commonality, instead of imagining a design failure in trivial text.

If you still imagine it, go apply the same reasoning to Daedalus.  You'll run into yourself (attached).

[lamontagne]

No, Winterberg 2015, like Daedalus, uses a Winterberg magnetic mirror nozzle to limit heat transfer.  Same basic thermodynamics, etc.

You've talked a lot about Daedalus, and you saw no thermodynamics problem there.  So you really should have recognized the plain Winterberg 2015 commonality, instead of imagining a design failure in trivial text.

If you still imagine it, go apply the same reasoning to Daedalus.  You'll run into yourself (attached).

Winterberg does not use a magnetic mirror to limit all heat transfer.  Yes, the magnetic field does keep the plasma away from the wall, preventing conductive and convective heat transfer from the plasma, but it is useless against radiative heat transfer.  So X-rays and neutrons, that are not affected by the field, go straight through and heat the wall.
The oscillating nature of the field also induces currents that heat the wall significantly. Hence the Eddy currents we have been discussing.
Winterberg, as well as the Dadalus designers, Bond and Martin, use other mechanisms of ICF to stop X-rays and Neutrons.  Mainly the very high density in the pellet core at the time of the maximum compression, that can absorb many of the neutrons.  Bond and Martin also propose entirely opaque plasmas to capture Bremstralhung, but the explanation is extremely brief and is one of the few elements that are not calculated, but hypothethised.  I have never seen any paper that proves that the early plasma from an ICF explosion would be opaque, but would love to see one if it exists.  I have read a number of paper that say that this phenomenon does not exist, that aneutronic fusion is anything but, and that in many cases Bremstralhung losses are too great for many of the fusion reactions proposed for heavier atoms.

And now, some eye candy, for all of those deeply fed up with this rather pointless discussion.

[LMT]

Winterberg does not use a magnetic mirror to limit all heat transfer.  Yes, the magnetic field does keep the plasma away from the wall, preventing conductive and convective heat transfer from the plasma, but it is useless against radiative heat transfer.  So X-rays and neutrons, that are not affected by the field, go straight through and heat the wall.
The oscillating nature of the field also induces currents that heat the wall significantly. Hence the Eddy currents we have been discussing.

No, Winterberg 2015 captures X-rays and neutrons in borated hydrogen plasma.  You should understand!  Beyond that, superconducting circuits would capture (lesser) field energy without Joule heating, leaving only a residual for reflector eddy currents.  Here hot metal radiates, as with Daedalus, with little if any need for coolant exhaust.  You republished BIS Daedalus thermal numbers uncritically because you didn't see a "design failure" demanding immense coolant mass.  Well, there isn't one, here or there.

A 3F fusion-drive tug for Starships would fire at a much slower rate, even 1000x slower than Daedalus; hence, with less heating.  Structures could be prototyped with "Boca Chica scrap", even today. 

Judging from recent text, many posters see "fusion drives" as something achievable "down the road", with future breakthroughs, someday...  3F has been overlooked here, repeatedly.  Regardless, the present reality of efficient 3F fusion -- with plausible options for ISRU methalox conversion and self-sufficient tritium breeding, no less -- should register.  I expect it to register, in the Advanced Concepts section of a spaceflight forum.

Fusion enthusiasts could step up and look for further improvements.

[edzieba]

No, Winterberg 2015 captures X-rays and neutrons in borated hydrogen plasma.

See the latter portion of  lamontagne's post that you missed/ignored:

Bond and Martin also propose entirely opaque plasmas to capture Bremstralhung, but the explanation is extremely brief and is one of the few elements that are not calculated, but hypothethised.  I have never seen any paper that proves that the early plasma from an ICF explosion would be opaque, but would love to see one if it exists.  I have read a number of paper that say that this phenomenon does not exist

An experimental measurement of the X-ray opacity of a 'borated hydrogen plasma' would be a good thing to link to to start with. Except that doesn't solve the whole problem anyway: even if a suspended plasma will absorb all of the X-ray flux... that energy has to go somewhere, so you still end up with radiant heating to deal with anyway. No free thermodynamic lunches.

[LMT]

even if a suspended plasma will absorb all of the X-ray flux... that energy has to go somewhere...

It's a rocket.  Energy that doesn't go into the structure goes out the back, by design.

-  The plasma of Winterberg 2015 exits the nozzle at ~ 30 km/s.

-  The plasma of Winterberg 2004 exits the nozzle, and solar system, at ~ 130 km/s.