Fusion with space related aspects thread

[Elmar Moelzer]

Not really news but 
https://aviationweek.com/defense-space/aircraft-propulsion/skunk-works-halted-nuclear-fusion-effort-2021

Yeah, the last publications indicated a massive size growth. Scaling laws just did not hold up.

[RON_P]

Helicity Space raises $5 million for fusion engine development

https://spacenews.com/helicity-space-raises-5-million-for-fusion-engine-development/

SAN FRANCISCO — Helicity Space, a California startup developing fusion engines for spaceflight, has raised $5 million in a seed funding round announced Dec. 11.

Helicity attracted funding from Airbus Ventures, TRE Ventures, Voyager Space Holdings, E2MC Space, Urania Ventures and Gaingels.

“We’re happy to be backed by long-term strategic partners of substance,” Helicity co-founder Stephane Lintner told SpaceNews. “We almost look at them as future clients.”

Helicity, founded in Pasadena in 2018, avoided publicity in its early years.

“The company took a lot of time dotting the i’s, crossing the t’s and lining up the right science advisors to make sure that before we raised capital, we de-risked the project as much as possible,” said Lintner, a former Goldman Sachs managing director with a Ph.D. in applied mathematics from the California Institute of Technology.

With the latest funding, “we’ll deliver a proof-of-concept fusion drive that the company is building,” Lintner said. “Before we put things in space, we need to demonstrate the full device working on Earth at smaller scale. The funding allows us to demonstrate the novelty of this concept.”

Deep Space Missions
Fusion power has been a staple of science fiction because it promises clean, plentiful energy. For spaceflight in particular, fusion engines could slash the travel time to Mars and beyond.

“If we really want to create this expansion, where we actually get to the asteroid fields or to deeper space, even to map it out and figure out what resources are there, you need a different kind of propulsion,” Lintner said.

In contrast to nuclear thermal or nuclear electric power, fusion “frees up much more energy in an extremely efficient way that requires very little fuel,” Lintner said. “Until recently fusion has always been very elusive.”

Helicity’s technology is based on the work of Setthivoine You, Helicity co-founder and chief scientist. You, a plasma physics researcher with a Ph.D. from Imperial College London, has published patents related to fusion drive.

Helicity’s magneto-inertial fusion method was “developed from the ground up with space propulsion in mind,” You said in August at an Interstellar Research Group Symposium.

Helicity’s “has developed a novel approach to fusion reactions, using multiple recombining plasma jets to create and control the conditions necessary for fusion to occur,” Airbus Ventures partner Lewis Pinault told SpaceNews by email. “With several years of research and meticulous supercomputer modeling to prove the viability of this approach, along with private sector investment, the Helicity Space team is now deploying and testing hardware to turn theory to reality.”

Reasonable Belief
Technology development and testing continues in Helicity’s Pasadena laboratory.

“It’s going to take a few years and it’s going to require capital,” Lintner said. “We’re just at the beginning of the journey, but we have reasonable belief that this may work. Given the importance of this type of propulsion for mankind, for our children, to keep Earth clean, we’re really excited with the prospect.”

Pinault added “fusion-based propulsion will revolutionize humankind’s ability to traverse deep space. From establishing settlements on other planets and moons to venturing beyond our solar system and to other capabilities long locked in the realm of science fiction, our collective capacity for space mobility will take one giant leap forward on the back of Helicity Space’s technology.”

Helicity strategic advisors include former NASA astronaut William Ready, a retired U.S. Navy captain and former NASA associate administrator; Alan Stern, former NASA’s Science Mission Directorate leader with a Ph.D. in astrophysics and planetary science from the University of Colorado, Boulder; and Simon “Pete” Worden, former NASA Ames Research Center director and retired U.S. Air Force brigadier general with a Ph.D. in astronomy from the University of Arizona.

[InterestedEngineer]

Helicity Space raises $5 million for fusion engine development

https://spacenews.com/helicity-space-raises-5-million-for-fusion-engine-development/

This is a pretty cool design.  It deals with several issues that to me were plaguing a lot of fusion drive proposals

1.  Fusion drives are still in part heat engines - the mass needs to move from tank to exhaust thus a positive pressure gradient for insane fusion pressures needs to happen, including the expansion of the exhaust components as they heat up.  Helicity solves this the way nature solves this problem in animal bodies - peristaltic compression (but a magnetic variety).  Compare to a compressor stage in a thermal rocket

2.  Direct design for generating thrust, instead of trying to modify a design that to date at over 50 years of applied research has not generated electricity.

3.  Early Isp gains with only a bit of it working.  Basically it'll started as a slightlly boosted electric ion drive, and then add efficiency over time to achieve the combo of thrust and exhaust velocity needed to become truly valuable in comparison to refuelable aerobraking chemical rockets.  That crossover is at about an isp of 2000-2500 if thrust / weight ratio is 1-2 orders of magnitude better than current ion drives.   This is the type of development trajectory (the kind with a reasonable starting point and an order of magnitude continuous improvements in pipeline) that allows a startup to truly suceed).

Has anyone collected the patents in one place?   would be fun to do some digging

[InterestedEngineer]

How convenient, Helicity has links to published papers

https://www.helicityspace.com/scientific-publications


https://www.helicityspace.com/scientific-conferences

[Solarsail]

I wonder how viable it would be to use Helicity's engine to generate power, if its exhaust is charged particles traveling linearly.  Could it run an MHD generator, and recapture unburned deuterium from each shot?  That could be valuable in either a terrestrial power generation context (if it somehow manages to get to net power before other reactor concepts) or in spaceflight, if a single engine can swap between propulsion mode and generator mode.

[Elmar Moelzer]

I wonder how viable it would be to use Helicity's engine to generate power, if its exhaust is charged particles traveling linearly.  Could it run an MHD generator, and recapture unburned deuterium from each shot?  That could be valuable in either a terrestrial power generation context (if it somehow manages to get to net power before other reactor concepts) or in spaceflight, if a single engine can swap between propulsion mode and generator mode.

Technically, it should be possible. I think they might have even mentioned that possibility in the past, but I might be remembering this wrong. So take it with a grain of salt.

[Joe_Camp]

Helicity Space raises $5 million for fusion engine development

https://spacenews.com/helicity-space-raises-5-million-for-fusion-engine-development/

This is a pretty cool design.  It deals with several issues that to me were plaguing a lot of fusion drive proposals

1.  Fusion drives are still in part heat engines - the mass needs to move from tank to exhaust thus a positive pressure gradient for insane fusion pressures needs to happen, including the expansion of the exhaust components as they heat up.  Helicity solves this the way nature solves this problem in animal bodies - peristaltic compression (but a magnetic variety).  Compare to a compressor stage in a thermal rocket

2.  Direct design for generating thrust, instead of trying to modify a design that to date at over 50 years of applied research has not generated electricity.

3.  Early Isp gains with only a bit of it working.  Basically it'll started as a slightlly boosted electric ion drive, and then add efficiency over time to achieve the combo of thrust and exhaust velocity needed to become truly valuable in comparison to refuelable aerobraking chemical rockets.  That crossover is at about an isp of 2000-2500 if thrust / weight ratio is 1-2 orders of magnitude better than current ion drives.   This is the type of development trajectory (the kind with a reasonable starting point and an order of magnitude continuous improvements in pipeline) that allows a startup to truly suceed).

Has anyone collected the patents in one place?   would be fun to do some digging

I am just getting started on fusion propulsion. I just finished reading a paper on Magnetic Fusion Plasma Drive by Florian Neukart. Should I start at the beginning of this thread, and do you have any recommendations on reading materials.

Joe

[LMT]

Helicity Space raises $5 million for fusion engine development

https://spacenews.com/helicity-space-raises-5-million-for-fusion-engine-development/

Early Isp gains with only a bit of it working.  Basically it'll started as a slightlly boosted electric ion drive, and then add efficiency over time to achieve the combo of thrust and exhaust velocity needed to become truly valuable in comparison to refuelable aerobraking chemical rockets.  That crossover is at about an isp of 2000-2500 if thrust / weight ratio is 1-2 orders of magnitude better than current ion drives.

Helicity hopes to surpass electric Isp with also 2+ OOM thrust-to-weight improvement when they switch to multi-GW self-sustained DHe3 fusion, in the 4th iteration of Drive tech.  (plot)

Might be a while.

[LMT]

Cross-post:  Boca Chica Fusion

[LMT]

A fusion comparison Helicity omitted -- Winterberg's fission-fusion-fission system (red) -- notionally incorporating ISRU MOX high explosive.

[LMT]

Cross-post:  a little fusion "same-and-different" challenge, with Mike Shot

[LMT]

Elmar et al.

...the best gain for NIF has been about 1.5 (fusion energy to laser energy).  As the entire laser array is just a few % in efficiency, it' still a long way to go.

Inertial confinement fusion vehicles will probably be quite large...

Technically, "inertial confinement" encompasses the old military explosive meaning, as well.  NIF may offer a path to electricity, but if electrical output isn't needed, and instead only propulsion, the other meaning can apply.  I've highlighted Winterberg's contributions, such as his fission-fusion-fission design:

Estimates indicate that a few kg of high explosives are sufficient to ignite such a “mini-nuke”, with a gain of
∼ 10^3, releasing an energy equivalent to a few tons of TNT, still manageable for the microexplosion
to be confined in a reactor vessel.

Checking the tables, it seems a softball-sized Winterberg system requires only ~ 0.3 grams of fissile core to give ISRU MOX a thousandfold propulsive gain.  Compare to posters' NIF hopes, e.g.:

...the gain you get is super high for NIF. I think maybe over 100 if you count only the energy going into the tiny fuel pellet. And because ignition was achieved, they may be able to get even higher gains. That helps a LOT.

Graphically, you see where Winterberg's thousandfold gain sits on the plot of specific energy vs. Isp, above.  The gain is already high enough for practical purposes, such as sending settlers to Mars in just one month -- a boost that may well have a business case down the road a bit, you know.

This thread has thousands of posts on space fusion.  Collectively you might use all you've typed and learned, applying your relevant info in that thread, where posters struggle, emotionally, with basics like the plot above.

(And Elmar, I see you're missing a few tricks.  Eyes open for potential solutions, always.)

[Elmar Moelzer]

Elmar et al.

...the best gain for NIF has been about 1.5 (fusion energy to laser energy).  As the entire laser array is just a few % in efficiency, it' still a long way to go.

Inertial confinement fusion vehicles will probably be quite large...

Technically, "inertial confinement" encompasses the old military explosive meaning, as well.  NIF may offer a path to electricity, but if electrical output isn't needed, and instead only propulsion, the other meaning can apply.  I've highlighted Winterberg's contributions, such as his fission-fusion-fission design:

Estimates indicate that a few kg of high explosives are sufficient to ignite such a “mini-nuke”, with a gain of
∼ 10^3, releasing an energy equivalent to a few tons of TNT, still manageable for the microexplosion
to be confined in a reactor vessel.

Checking the tables, it seems a softball-sized Winterberg system requires only ~ 0.3 grams of fissile core to give ISRU MOX a thousandfold propulsive gain.  Compare to posters' NIF hopes, e.g.:

...the gain you get is super high for NIF. I think maybe over 100 if you count only the energy going into the tiny fuel pellet. And because ignition was achieved, they may be able to get even higher gains. That helps a LOT.

Graphically, you see where Winterberg's thousandfold gain sits on the plot of specific energy vs. Isp, above.  The gain is already high enough for practical purposes, such as sending settlers to Mars in just one month -- a boost that may well have a business case down the road a bit, you know.

This thread has thousands of posts on space fusion.  Collectively you might use all you've typed and learned, applying your relevant info in that thread, where posters struggle, emotionally, with basics like the plot above.

(And Elmar, I see you're missing a few tricks.  Eyes open for potential solutions, always.)

I am not sure what post by me you are referring to specifically...

[LMT]

I am not sure what post by me you are referring to specifically...

None in particular, but you might start, say, with last year's post on Project Orion / Helicity / tritium breeding.  You could compare and contrast all that in context of requirements for one month to Mars, e.g.:

Fusion tug concepts:

1.  Winterberg's 3F microexplosion engine and its performance 1 2 3

2.  Tug prototype / scaling 1 2 3 4

3.  Attempting self-sufficient tritium breeding

Or just as things might come to mind, you know.

[Elmar Moelzer]

I am not sure what post by me you are referring to specifically...

None in particular, but you might start, say, with last year's post on Project Orion / Helicity / tritium breeding.  You could compare and contrast all that in context of requirements for one month to Mars, e.g.:

Fusion tug concepts:

1.  Winterberg's 3F microexplosion engine and its performance 1 2 3

2.  Tug prototype / scaling 1 2 3 4

3.  Attempting self-sufficient tritium breeding

Or just as things might come to mind, you know.

One comment I will make is that reactivity vs temperature is not everything. There are other things that factor into all of this, e.g. density, Te:Ti, how effectively the energy can be converted to thrust, etc. And then mass of the shielding and cooling required. If your D-T engine has a T/W ratio that is say 5 times that of the D-He3 engine, but loses all of that to the extra shielding and cooling, then you have gained nothing but a lot of headaches with the other disadvantages.

[LMT]

...start, say, with last year's post on Project Orion / Helicity / tritium breeding.  You could compare and contrast all that in context of requirements for one month to Mars, e.g.:

Fusion tug concepts:

1.  Winterberg's 3F microexplosion engine and its performance 1 2 3

2.  Tug prototype / scaling 1 2 3 4

3.  Attempting self-sufficient tritium breeding

Or just as things might come to mind, you know.

One comment I will make is that reactivity vs temperature is not everything. There are other things that factor into all of this, e.g. density, Te:Ti, how effectively the energy can be converted to thrust, etc. And then mass of the shielding and cooling required. If your D-T engine has a T/W ratio that is say 5 times that of the D-He3 engine, but loses all of that to the extra shielding and cooling, then you have gained nothing but a lot of headaches with the other disadvantages.

Well, first things first, yes?  Winterberg's 3F softball looks ok from a specific-energy perspective?  (In discussion, it's good to start with positive points, if any.  It keeps participants engaged.)

"You asked about the temperature."

With these microexplosions, the high-explosive shell captures "a good fraction" of high-energy fast neutrons in plasma (Winterberg 2004).  And as you saw above, I think you could add an LCH4 cap to capture much of the remaining fast-neutron energy outside the tug.  Beyond that, you might add boron not just to the dispersive backing disk, but to the cap also, to sop up more thermal neutron energy in the plasma, if that's desired.

In much that same spirit, Winterberg 2015 surrounds that core with a borated hydrogen sphere.  Here again, much neutron energy is captured in plasma.  He emphasizes that a magnetic mirror prevents impingement of the plasma exhaust on the metal reflector, limiting heating.  For these reasons, coolant requirement would be low.  His ballpark:

The expanding fire ball compressing the magnetic field will there generate surface currents in the metallic reflector, making a magnetized plasma layer protecting the reflector from the hot plasma. The meter-size hydrogen sphere of the mini-fusion bomb is transformed into a fireball with a temperature of ~ 10^5 K...  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...

If the fireball expands from an initial radius of R0 ~1 m to R1 ~10 m, the pressure goes down to... ~10^3 atm..., less than the tensile strength of steel.

At this pressure, the magnetic field strength at the surface of the steel will be of the order 10^5 Gauss. The energy released by the eddy currents in the reflector can hardly be more than 10% of the energy released in the fusion explosion. The mass of a meter-size ball of liquid hydrogen is of the order 0.1 tons, such that 0.01 tons of liquid hydrogen would be available for the cooling of the reflector.

Winterberg 2015 aims to launch from Earth, much like the original Project Orion.  Here his fusion pulses cycle at 1 Hz to reach orbit quickly; that must give something like a pulse-averaged 2+ g.  In contrast, the notional tug concept needs only modest acceleration in space; I'm looking at a pulse-averaged 0.2 g, simply to achieve 12-hour turnaround.  Lower acceleration gives lower averaged heat flux.  Given that his Earth-launch cadence would require only ~ 10 kg of LH2 for cooling after each detonation, I'm debating whether any coolant is needed on a tug's reflector.

[InterestedEngineer]

The expanding fire ball compressing the magnetic field will there generate surface currents in the metallic reflector, making a magnetized plasma layer protecting the reflector from the hot plasma. The meter-size hydrogen sphere of the mini-fusion bomb is transformed into a fireball with a temperature of ~ 10^5 K...  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...

If the fireball expands from an initial radius of R0 ~1 m to R1 ~10 m, the pressure goes down to... ~10^3 atm..., less than the tensile strength of steel.

At this pressure, the magnetic field strength at the surface of the steel will be of the order 10^5 Gauss. The energy released by the eddy currents in the reflector can hardly be more than 10% of the energy released in the fusion explosion. The mass of a meter-size ball of liquid hydrogen is of the order 0.1 tons, such that 0.01 tons of liquid hydrogen would be available for the cooling of the reflector.

Where does the energy from all those eddy currents go?  10% is a lot of energy.

Capturing some of that into capacitors might be useful to power other things, but that's still a lot of energy.  Putting it to work in propulsion would be nice

[LMT]

The expanding fire ball compressing the magnetic field will there generate surface currents in the metallic reflector, making a magnetized plasma layer protecting the reflector from the hot plasma. The meter-size hydrogen sphere of the mini-fusion bomb is transformed into a fireball with a temperature of ~ 10^5 K...  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...

If the fireball expands from an initial radius of R0 ~1 m to R1 ~10 m, the pressure goes down to... ~10^3 atm..., less than the tensile strength of steel.

At this pressure, the magnetic field strength at the surface of the steel will be of the order 10^5 Gauss. The energy released by the eddy currents in the reflector can hardly be more than 10% of the energy released in the fusion explosion. The mass of a meter-size ball of liquid hydrogen is of the order 0.1 tons, such that 0.01 tons of liquid hydrogen would be available for the cooling of the reflector.

Where does the energy from all those eddy currents go?

You'd expect a shifting / balancing of energy under Maxwell's equations and black-body radiation, for:

1.  plasma exhaust
2.  reflector structure
3.  reflector superconducting magnetic mirror circuits
4.  superconducting regenerative shock absorber circuits
5.  some notional, additional superconducting magnetic energy storage (SMES) units, capacitors, or bleed-off

Putting [that energy] to work in propulsion would be nice...

Repelling plasma off the reflector does serve the propulsion unit.  And have you noticed the 3F system's native specific energy and Isp, and potential thrust augmentation from "waste" neutrons?  Do you see how that much could meet a tug's exceptional propulsion requirement, as-is?

[LMT]

Cross-post:  Breeding Tritium in Space

Elmar, it might be interesting to see whether thermal-neutron breeding in 6Li, by itself, could give tritium self-sufficiency in a Winterberg 3F fusion drive for a notional Starship tug. 

Rationale:
If thermal neutrons should prove sufficient for breeding, the escaping fast neutrons could be harnessed exclusively for thrust.  That is to say, the notional LCH4 cap mass could be maximized, to give max thrust augmentation from those "waste" fast neutrons, which comprise a fusion energy fraction that is typically ignored in thrust calc.  Given that ~ 80% of the DT fusion energy is released in fast neutrons, such maximized thrust augmentation might give the highest effective specific energy number among fusion-drive designs having tritium self-sufficiency option (excepting antimatter-catalyzed concepts).

Phrasing the question:
Is there a useful ballparking approach to quantify 3F thermal-neutron breeding in 6Li? 

Notes: 
We might simplify with a uranium-only 3F model, instead of uranium-thorium.  Also, as expected, we see that enrichment in either 235U or 6Li eases self-sufficiency in modeled fusion-fission hybrid breeders (Acır et al. 2009, equation 1).  For a promising 6Li enrichment approach, see Giegerich et al. 2019.

Related post: 
The nuclear physics of why tritium is a challenge for fusion engineering
- Nick Hawker, First Light Fusion CEO, 1/22/23

Image:
Tritium breeding in 6Li and 7Li.  Nick Hawker.

Refs.

Acır, A., Alakoç, N.P. and Yıldız, K., 2009. Estimation of neutronic performance in a hybrid reactor with regression analysis. Journal of fusion energy, 28, pp.427-433.

Giegerich, T., Battes, K., Schwenzer, J.C. and Day, C., 2019. Development of a viable route for lithium-6 supply of DEMO and future fusion power plants. Fusion Engineering and Design, 149, p.111339.

[lamontagne]

The expanding fire ball compressing the magnetic field will there generate surface currents in the metallic reflector, making a magnetized plasma layer protecting the reflector from the hot plasma. The meter-size hydrogen sphere of the mini-fusion bomb is transformed into a fireball with a temperature of ~ 10^5 K...  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...

If the fireball expands from an initial radius of R0 ~1 m to R1 ~10 m, the pressure goes down to... ~10^3 atm..., less than the tensile strength of steel.

At this pressure, the magnetic field strength at the surface of the steel will be of the order 10^5 Gauss. The energy released by the eddy currents in the reflector can hardly be more than 10% of the energy released in the fusion explosion. The mass of a meter-size ball of liquid hydrogen is of the order 0.1 tons, such that 0.01 tons of liquid hydrogen would be available for the cooling of the reflector.

Where does the energy from all those eddy currents go?  10% is a lot of energy.

Capturing some of that into capacitors might be useful to power other things, but that's still a lot of energy.  Putting it to work in propulsion would be nice

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.