Magneto Inertial Fusion Rocket

[shynung]

For some of you, this might be old news. But I think it's worth discussing, if even for a little while.

Back in the early 2010s, a paper was published about the rocket motor named as the title of this thread. The magneto inertial rocket was powered by fusion, using lithium as propellant.

It works like this: fusion fuel (D/T, D/D, or D/He3) is turned into a blob of plasma in a field-reversed configuration, and injected into a chamber. Also injected into the chamber are metal foils, made out of lightweight metals such as lithium or aluminium. The foils and plasma injection is timed so that both converges at the chamber's end, inside the throat, at several km/sec. Aided by magnetic coils located strategically around the throat, the inertia of the metal foils compresses the plasma of fusion fuels to ignite the fusion reaction. Just after this happens, the plasma blob containing fusion products and what remains of the metal foils move into the magnetic nozzle diverging section, where it expands and converts its pressure into velocity, which ends up throwing the plasma out the back of the nozzle, generating thrust.

Main advantages compared to more traditional nuclear thermal rockets are:
- uses solid propellants, which have high density, lowering tankage mass for a given dV budget.
- low thermal loads on motor components, since the plasma never touches the motor itself, confined by magnetic coils, reducing radiator mass.
- fusion fuel is covered in foils at the moment of fusion, limiting emitted radiation.
- lower energy requirements compared to other fusion methods, only need power to run the coils.

The thrust generated isn't much - Atomic Rockets claimed a 13.8 kN thrust with pulses at 14 seconds interval - but it gets 5000 seconds of Isp. As a bonus, if the nozzle is replaced with a MHD generator, it effectively becomes a fusion power plant.

What are your thoughts about the concept? Feasible? Foolish?

[Scotius]

I'm not sold on any kind of pulse drive. It's hard on structure of the ship and uncomfortable for the crew - thus requiring some kind of amortisation, which will complicate ship's project. Also, why cover the fuel with foil inside the engine, complicating the process and risking uneven wrapping? Wouldn't it be better and simpler to inject lithium already contained in metal-covered pellets?

[RainDreamer]

A rocket named Magneto? Was it named by a professor named Xavier?

[magnemoe]

6 hours ago, Scotius said:

I'm not sold on any kind of pulse drive. It's hard on structure of the ship and uncomfortable for the crew - thus requiring some kind of amortisation, which will complicate ship's project. Also, why cover the fuel with foil inside the engine, complicating the process and risking uneven wrapping? Wouldn't it be better and simpler to inject lithium already contained in metal-covered pellets?

Benefit of this design is that you don't need break even fusion, current designs has better ISP and TWR than vasmir because of the fusion effect, 
Its not an orion, yes its pulsed but the pulses are pretty easy to handle, an car engine is also pulsed  Still it will give more stress than an continuous burn engine and is an pretty complicated design. 

[UmbralRaptor]

Assuming you can avoid putting more energy into compressing the components than you get from fusion (good luck), sure, why not? Isp sounds comparable to upper end gas core NTR. Ions can do better, but given that HiPEP put out over 4 orders of magnitude less thrust...

[shynung]

8 hours ago, Scotius said:

I'm not sold on any kind of pulse drive. It's hard on structure of the ship and uncomfortable for the crew - thus requiring some kind of amortisation, which will complicate ship's project. Also, why cover the fuel with foil inside the engine, complicating the process and risking uneven wrapping? Wouldn't it be better and simpler to inject lithium already contained in metal-covered pellets?

We do have shock absorbers. Using them as part of the thrust structure seemed to be an obvious solution. These can be as simple as gas pistons separating the engine components and the rest of the ship.

Combining fusion fuel and foil propellant would mean the compression ignition would be done purely with coils, which would raise energy requirements. The separate fuel-propellant scheme is set up to lessen the load on the coils by using the foil's kinetic energy.

3 hours ago, RainDreamer said:

A rocket named Magneto? Was it named by a professor named Xavier?

The lead was someone named Slough, actually.

15 minutes ago, UmbralRaptor said:

Assuming you can avoid putting more energy into compressing the components than you get from fusion (good luck), sure, why not? Isp sounds comparable to upper end gas core NTR. Ions can do better, but given that HiPEP put out over 4 orders of magnitude less thrust...

We don't even need break even fusion, because the generated energy goes wholly to propulsion. Fusion was simply a means to heat the propellant, which in this case was the metal foils.

[Streetwind]

FYI, this engine isn't just a concept - they're trying to build it right now. A timeline published in 2012 called for a full scale ground prototype by 2020, and an orbital test flight by 2025.

Currently under developed at MSNW LLC. NASA is interested and has been supplying some funding.

 

In the meantime, if you want to play with it in KSP, check Nertea's Far Future Technologies (currently in alpha). It has this engine and many others.

Edited August 8, 2016 by Streetwind

[shynung]

1 hour ago, Streetwind said:

In the meantime, if you want to play with it in KSP, check Nertea's Far Future Technologies (currently in alpha). It has this engine and many others.

Oh, I already got it; just recently got active in that thread for this reason. Doesn't have MIF yet (non-AM engines are limited to Z-pinch microfission/microfusion, and the NSWR), unfortunately, but still quite impressive nevertheless.

[Bill Phil]

Why do we keep avoiding nuclear electric? It's obviously going to get high performance. We've put 10+ megawatt reactors in subs since the 50s. We should do it in space. It has issues, of course. Shielding is one of the big ones, plus the danger of a pressurised part exploding (although they may use electro thermal devices). But the performance is so high, it's worth it. At the very least for probes.

On topic: this fusion engine sounds promising. Hope all goes well.

[hms_warrior]

Shielding is actually a small problem whit nuclear reactors in space....trying to keep a 50 MW reactor from melting if you do not have a nice ocean around to dump heat into is the real problem ...that and public relations of course.

That's one of the nicer parts of this engine...the hot stuff get ejected to space.

Edited August 8, 2016 by hms_warrior

[shynung]

45 minutes ago, Bill Phil said:

Why do we keep avoiding nuclear electric? It's obviously going to get high performance. We've put 10+ megawatt reactors in subs since the 50s. We should do it in space. It has issues, of course. Shielding is one of the big ones, plus the danger of a pressurised part exploding (although they may use electro thermal devices). But the performance is so high, it's worth it. At the very least for probes.

TWR issues, maybe? If it takes forever to get the ship going, then it can't use Oberth effects, and needs to use spiral trajectories that are much less efficient than straight-up Hohmann transfer trajectory.

Also, naval reactors are floating in coolant. Sure, they can't exactly pipe seawater into the reactor cooling lines, but they don't have to carry big radiators, either. They're also optimized for power/volume ratio rather than power/mass ratio, so not an ideal choice for space applications.

Of course, after we get through all the hoops, we do get impressive specific impulse out of electric thrusters. So that's that.

[Bill Phil]

9 hours ago, shynung said:

TWR issues, maybe? If it takes forever to get the ship going, then it can't use Oberth effects, and needs to use spiral trajectories that are much less efficient than straight-up Hohmann transfer trajectory.

Also, naval reactors are floating in coolant. Sure, they can't exactly pipe seawater into the reactor cooling lines, but they don't have to carry big radiators, either. They're also optimized for power/volume ratio rather than power/mass ratio, so not an ideal choice for space applications.

Of course, after we get through all the hoops, we do get impressive specific impulse out of electric thrusters. So that's that.

Of course there are challenges. But NASA's already flown a reactor in space, and the soviets flew quite a few. All of them were very low power, though.

We should at least use them for probes, like in Project Prometheus, since they can allow for some really high ISP engines to be used in the outer solar system.

Manned use would be an even bigger challenge, of course. 

Low TWR vehicles can still take advantage of the Oberth Effect. It'll have to take multiple orbits though, and apply Dv only near Periapsis. 

[shynung]

@Bill Phil Regarding probes, I agree that we should start using nuclear-electric propulsion. Alternatively, we can also use radioisotope stirling generators to power the electric rocket motors, if a full-blown reactor is deemed too large.

On larger vessels, I'd put my bet on either this motor (MIF), or its competitors VASIMR, gas-core NTR, or Zubrin's NSWR.

[ChainiaC]

VASIMR? Meh, I'd rather go with the more advanced, powerful and versatile ELF (electrodeless lorentz force) thruster myself.

[Nefrums]

Looking at the technology involved this looks like most feasible high isp engine suggestion I have seen to date.

It requires about the same amount of electric power than is generated on ISS, radiation is negligible, no need for extensive heat radiators. Thrust is low enough that pulsing is not to big of a problem but high enough to get some use of the oberth effect. It is also small enough that it could be launched to orbit on net gen rockets (SLS etc.)

 

 

 

[ChainiaC]

I must admit that is beautiful!

I'm still more a fan of nuclear electric, but I know that sending big reactors into space is not going to happen anytime soon and it is actually pretty neat that this engine uses fusion energy that has such low electric power requirement.

Edit: Also I can see where Nertea probably got the inspiration for the Lithium tanks in NFP

 

Edited August 30, 2016 by ChainiaC

[magnemoe]

2 hours ago, ChainiaC said:

I must admit that is beautiful!

I'm still more a fan of nuclear electric, but I know that sending big reactors into space is not going to happen anytime soon and it is actually pretty neat that this engine uses fusion energy that has such low electric power requirement.

Edit: Also I can see where Nertea probably got the inspiration for the Lithium tanks in NFP

 

If you had more power you could pulse it more often and getting many times the trust. 

[shynung]

@ChainiaC Yeah, I don't think we'll get spaceborne nuclear reactors for a while. Not unless we start going interplanetary at an industrial scale.