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NASA-backed fusion engine could cut Mars trip down to 30 days (theregister.co.uk)
162 points by kristianp on Apr 10, 2013 | hide | past | web | favorite | 158 comments



Arguably we've had "fusion drive" for spaceships ever since Project Orion. Very simply, build a ship with a big shield in the back, throw nuclear bombs out behind the ship, detonate, the shock and radiation hits the plate (some ablates, but it's still fairly study and safe), and some kind of shock absorber system pushes the spaceship forward. Repeat. You can feasibly get to 0.10c with this, using 1960s technology, and really big ships.

I think most of the earlier designs involved fission bombs, but there's no reason you couldn't use fusion bombs, and maybe even some kind of laser or magnetic means of initiating fusion. Which seems to be exactly what UW is talking about here.

http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsi...

A lot of the engineering and physiological problems of a Mars mission go away if you have the ability to move huge masses between Earth and Mars fast. You can skip the low energy launch windows and just go for a short on-Mars trip, rather than needing to loiter for a year or two between windows. You don't need to worry about supplies in space and radiation issues for a year-long transit. etc.


Surely that's like saying we've had nuclear submarines since Jules Verne wrote "20,000 leagues under the sea" insofar as Project Orion was little more than science fiction and didn't involve fusion drives ("atomic bomba" would be fission).

(Verne's Nautilus was powered by primitive batteries.)


Project Orion was much more than science fiction (http://www.scribd.com/doc/28668567/Nuclear-Pulse-Space-Vehic...) though it was much less than operational. Very big Orion spaceships would have used fusion explosions (http://galileo.phys.virginia.edu/classes/321.jvn.fall02/Dyso...), but not the relatively small ones that were subjected to detailed analysis.


You say "conceptual design" and I say little more than science fiction. Potato, potato -- some kind of solid fuel rocket is going to lift a shield strong enough to protect a crew with 90 days of "emergency" supplies from small stomic bombs going off... Right. And this is for a lunar mission!

There's more detailed stuff out on the warp drive NASA has funded study on, meanwhile the grandparent made it sound like someone had built one of these things (only with fusion bombs) in 1952 and it was rusting in a shed somewhere.


Then we've basically been on the moon for centuries now. Just because we can theoretically build something with known physics doesn't mean we have e.g. the material knowledge to actually construct the spaceship. Also, there's this issue of slowing down, and of how to get that spaceship with that much fuel out of the atmosphere, and how to get that spaceship back.... I would say we have a long way to go before claiming we "have" a fusion drive in a spaceship.


It's pretty much like rocket jumping.


> Arguably we've had "fusion drive" for spaceships ever since Project Orion. Very simply, build a ship with a big shield in the back, throw nuclear bombs out behind the ship, detonate, the shock and radiation hits the plate (some ablates, but it's still fairly study and safe), and some kind of shock absorber system pushes the spaceship forward. Repeat. You can feasibly get to 0.10c with this, using 1960s technology, and really big ships.

I never understood how the blast alone can propel the ship. Don't you also need to eject mass from a nozzle to move forward - in which case, it's just like a regular jet, you just replace part of the fuel with nukes?


Nozzles are basically just a more efficient version of this, since they don't waste as much energy which would escape out the sides (it's instead contributing to internal pressure, which pushes everything out the open end more quickly). Burning rocket fuel expands it rapidly, which is essentially all a bomb does. The downside to a nozzle is that you have to keep the internal pressure low enough that it doesn't rupture. This is far less of a problem with an Orion-style ship.

Think of an explosion. They produce moving walls of compressed air that flings stuff around. Though this is just because it's in air, it's a lot of energy. The same amount of energy is still being released if you blow it up anywhere else. (ignoring bonus 'free' energy from e.g. burning the air itself)

Take the explosion out of air, and you still have a 'shock wave' from the material which made up the bomb, and electrons / photons / whatever else materialized from that much energy being released in a tiny space. And it's all moving very quickly.

When it hits your ship's back-end, it gives it a kick. Obviously far less than the total energy released (whatever % of the sphere of expanding energy which your ship covers), but still something. If the explosion is big enough, or close enough, you are still talking an immense 'kick'. And since you have no relatively-fragile nozzle (just an arbitrarily big, thick wall), the force can be many many times greater than a normal rocket.

So to make it survivable, you probably need a big ship and some kind of impact-absorber to take the shock out of it, and / or lots of small bombs that won't kill everyone due to acceleration. Or just get rid of the squishy humans and crank up the proximity / bomb size to whatever you feel like.


Part of the mass in the fuel in the bomb is converted to photons; photons are massless but carry momentum.


I would never have thought about that. That just this is sufficient to push the ship forward is amazing.


There's also the fissile material involved, but I couldnt tell you what proportion of the energy is disappated through heat and what proportion is dissapated in light.

Everyone has seen the videos of the atomic bomb going off - that massive release of heat and energy that literally vaporizes mass that is close to the epicenter. Now imagine that reaction in space where the heat can't be disappated through atmosphere, water, or earth. All of that energy has to go somewhere, so it's all stored in whatever fissile material is left after the bomb goes off and dissapated through light and radiation.

I really wish I had some numbers for how hot that remaining material would get - even thinking about all the heat released in an atomic bomb concentrated into such a small amount of mass absolutely boggles the mind.


By the way, it's worth pointing out, to those who want to make a judgement on the reasons project Orion could not be implemented nowadays, that nuclear detonations are effectively a modern tabu.

This tabu is effective, has proven extremely useful (no detonations of nukes in a war since 1945) and thus cannot be considered the sign of a scientifically ignorant society.

Having said that, Orion would be quite cool.


We've had hundreds (or thousands, if you count sub-design-yield) detonations since 1945, including several in space (Hardtack Teak and Orange, and USSR equivalents).

And lots of them were for purely posturing purposes, with little scientific or direct weapons-testing value.

The US probably could have pulled off something like Orion in the 1990s or maybe even today, since there's not a direct cold war threat. Domestic politics probably kill it, though, but if it were branded as "nuclear pulse drive" with sub-10kT pulses, it might be possible.


You can't launch an Orion spaceship without violating the https://en.wikipedia.org/wiki/Partial_Nuclear_Test_Ban_Treat.... Also given the estimated 0.1 to 1 human deaths from cancer per launch (I am using Freeman Dyson's estimate here), it is hardly a politically viable vehicle.


>given the estimated 0.1 to 1 human deaths from cancer per launch (I am using Freeman Dyson's estimate here), it is hardly a politically viable vehicle.

Considering that one coal plant statistically kill about 70 people per year due to air pollution, I think it's more a matter of insufficient political power than the product of rational policy.


The cancer increase would be for launching from the ground/atmospheric use, which is a non-starter. I'm talking about use to run an orbital shuttle/tug/etc. between Earth and Mars. It would never enter atmosphere, and probably be constructed in space.

The US has enough weapons that it could comfortably withdraw from the treaty, or claim that these launches are not "tests" but rather some other use.


The cancer increase was from fallout. If you use it within Earth orbit, you still have significant fallout.


You don't really get fallout in the space.

The fallout is from neutron radiation of the ground, which doesn't happen in space. The amount of direct radiation from the uranium that is used is actually quite small.

And it would be trivial to point the exhaust away from earth. Space is full of radiation anyway, from the sun.


The fallout is from neutron radiation of the ground, which doesn't happen in space. The amount of direct radiation from the uranium that is used is actually quite small.

Can you cite this? I think the major dose component of nuclear fallout is from fission products, not neutron activation products. For example, skimming through these appendices on dose calculations from historic nuclear weapons tests [1](e-h), most of the significant radioisotopes are either fission products, or transuranic activation products from the weapon (e.g. Am-241). The environmental activation products discussed, C-14, Mn-54, Fe-55, and Co-60, are much less significant.

[1] http://www.cdc.gov/nceh/radiation/fallout/


It's a matter of quantity - a ground burst produces enormous amounts of radioactive material. An air (or space) burst only has a few KG of radioactive material.

From: http://www.fas.org/nuke/intro/nuke/effects.htm

"Air Bursts. .... there is essentially no local fallout from an air burst."

"Surface Burst ..... In contrast with air bursts, local fallout can be a hazard over a much larger downwind area than that which is affected by blast and thermal radiation."


I think you're misunderstanding that reference. The amount of radioactive material is not that different; the distinction is that a ground burst localizes some of it at ground zero. It creates a small area which will be an acute radiation hazard for a short time. An air burst gives a very large, diffuse, atmospheric plume.

In the maps from the CDC link, large areas -- whole states (check out pages f29-f35) -- are contaminated with low levels of airborne radioactive fallout. From the isotope data, it's clear most of this is from the weapons, not environmental activation products. The doses are too low to be immediately dangerous (<1 mSv), but can have chronic health effects, as a slightly increased cancer risk.


You can tune your weapon to have MUCH lower fission products; essentially the smallest size fission primary you can (ideally, with boosters), and then a big fusion stage and no U-238 tamper. Conventional thermonuclear weapons are usually fission-fusion-fission since a U-238 casing for the third stage is a cheap and compact way to scale up the weapon, but that last fission stage is responsible for >95% of the fission products/long lived pollution. A "neutron bomb"/ERW/etc. is one application of the low-radioisotope weapon (and a "dirty bomb", a non-critical radiological weapon, is the other extreme).

I'm still hoping fission-free fusion weapons are not possible before I can live somewhere other than Earth, since all arms control essentially rests of preventing access to fissile materials. Once you eliminate that gate, it becomes much easier for a clandestine group to build a weapon. Pure fusion weapons would be amazingly destabilizing and, if they were approximately as hard to make as seems likely, would absolutely get used by some group.


I would not have thought this, but you are right.

I would guess that the EMP would be dangerous to satellites, but I'm sure there are ways to mitigate that as well.



That's not really how fallout works. Fallout occurs primarily when you detonate a bomb near the ground or the water, causing it to suck up a bunch of dirt/water, irradiate it, and distribute it throughout the atmosphere. With a fusion bomb, you could end up with some leftover plutonium from the fission stage, but that's not the primary source of fallout.


Didn't Dyson's son write in the book that part of the reason for the treaty's signing was internal politics to kill a competitor to NASA?

1. Those 0.1-1 dead is from a period of much worse cancer treatments than will be available a few decades after an Orion launch.

2. It is bad risk counting. The cost per life is a factor whenever e.g. roads are built and speed limits are set. ("We will get ~ X less deaths/decade if we build the motorway differently, but it would cost over our limit for $/life".) Also, just transporting materials/people when designing/building an Orion ought to be a lot more than one dead.


We've had hundreds [...] detonations

None of them intended to kill other people, which is kind of the whole point of the taboo, not the detonation itself.

Plus, currently there is a kind of informal moratorium.


Do you mean 'taboo', as in something that's considered off-limits due to cultural sensitivities? (Wondering out loud if the etymology is similar to voodoo and related suspicious stuff)


"Taboo" derives from the Polynesian (Māori or Tongan) "tabu" systems of social control. Wikipedia has a decent overview.


Yes, taboo. I suffer a bad case of EuroEnglish.


and you think that getting x nuclear bombs into orbit is safe?

and even when all bombs go into space without incidents, having them there until start is no risk neither?

i think something more conventional would be better, even when less economically ...


As others point out, nuclear bombs do not spontaneously go off. If they were that easy to accidentally trigger, building them would be no big deal and we wouldn't be talking about nuclear vs. non-nuclear countries to this day.

Furthermore, everything is space is already a weapon. The very act of being in space and not falling back to Earth means you are loaded up with enough kinetic energy to be going several miles per second. You don't need nuclear bombs to be a weapon in space, a bucket of sand is a deadly weapon. Militarization of space refers to things other than merely putting "big bombs" in space, where they are surprisingly useless. (Even the EMP is less useful than you'd think; space is already a sea of radiation so everything up there is already hardened against it.)


You won't have an EMP in space - the EMP is generated by the motion of intensely electrically charged pieces of atoms acting against the magnetic field of the earth, and by electrons that were launched from atoms by the gamma ray pulse.

There is a solar magnetic field, but it's much weaker, so wouldn't make much of an EMP, and there is no atmosphere is space so the gamma rays don't accelerate any electrons.


You won't have EMP in deep space. Earth orbit is still "space".

High-altitude nuclear explosions (which produce the most intense EMP) work better above the Kalman line: http://en.wikipedia.org/wiki/File:High_altitude_EMP.gif

There are also special EMP weapons that don't require nuclear explosions.


That graph tops out at 300km, but even LEO is 2,000 km. (Although you can orbit as low as 160km - why would you for this?)

And I've never heard of a Kalman line and google comes up with nothing.


LEO is below 2000 Km, and is typically 300-500 Km. http://en.wikipedia.org/wiki/Low_Earth_Orbit


I don't think anyone thinks it's a particularly practical idea these days - for the reasons you identify.

However, it seems a bit of a shame that for all of the 2000+ nuclear weapons tests and tens of thousands of nuclear weapons built we never did anything as constructive as flying an Orion.


You can pack materials so that a failed launch will not create leaks.

The real problems for the Orion are political and frying of satellite electronics, iirc.


Mostly political. You could presumably do the detonations with the moon in between for a while, and it's not like space outside the Van Allen belts is particularly low energy, either, so GEO satellites are shielded.


i hate it when problems are "political" - or more correctly, that the general public's ignorance and fear retarding progress.


If I had ~10k nuclear weapons, I'd no longer have political problems.


I think you would suddenly have a great many political problems.


Well, combustion engine in my car is not very conventional either by XIX century standards. Maybe we should ride horses?

Why you make assumption that bombs must be delivered to space vs constructed there from resources mined in asteroids?


Plutonium is a synthetic element, requiring a nuclear reactor to create, then must be purified. Uranium is currently unknown in asteroids, and even if it were found would require refining with thousands of large centrifuges.

Converting uranium to uranium hexafluoride, centrifuging it over and over, then converting it back requires massive industrial facilities, currently impossible in space.


What about moon?

I'm pretty sure that smart people will figure out the solution. I just wanted to point out that most probably we can find solutions that are safe enough and the only limiting factor is our imagination (or lack of it specifically).


Plutonium ain't easy, so you'd probably want to ship pre-made pits into orbit (we've got plenty already made), preferably one at a time so we don't get a big critical mass of plutonium sitting in a desert in case the rocket crashes.


Why wouldn't it be safe? Nuclear bombs don't just explode by accident or when they are hit by something, they need to be deliberately triggered, so I wouldn't estimate the danger of this to be very big.

Furthermore, nuclear weapons have been sent to space before, both for regular long-range missiles and for EMP-like tests.


Something is rotten in Denmark. If this project achieves a sustained fusion reaction as claimed, that represents a huge breakthrough, and not just for space propulsion, but for the general topic of fusion power.

If it succeeds, it would sweep away all present fusion reaction prototype methods, including the well-tested but so far ineffective( * ) tokamak and laser-fusion approaches.

* By "ineffective" I mean none of them has reached the break-even point, that point where more energy is released than is required to initiate the reaction in the first place.

The article doesn't say whether the prototype device has actually succeeded in igniting a sustained fusion reaction. If it does, it would quickly move beyond its present goal of producing a more effective source of space acceleration and would answer some longstanding questions about fusion power itself.

The fact that this isn't being discussed leads to my statement above -- something is rotten in Denmark. Either the project is overselling its possibilities, and/or it can't really achieve fusion break-even.

Speaking hypothetically, if the device could produce a sustained fusion reaction with substantial power, it could be scaled up and used to propel a spacecraft to Mars in much less than 30 days. Assuming a sustained acceleration of 1 g, the hypothetical craft could accelerate for 1/2 the trip, turn around and decelerate for the other 1/2 of the distance, arriving at Mars with zero velocity. Apart from minimizing travel time, this hypothetical profile would prevent the bone loss that accompanies sustained time at zero-g.

Making the above assumptions, and assuming that Mars is at a close approach point in its orbit, the travel time could be as little as ... wait for it .. 50 hours.

Derivation:

1. Distance d (meters) for acceleration a (m/s^2) and time t (seconds): d = 1/2 a t^2

2. Time t for distance d and acceleration a, assuming 1/2 acceleration and 1/2 deceleration: t = 2 sqrt(d/a)

3. Result for Mars close approach (7.834e10 meters) and acceleration of 1 g: 49.64 hours.

Again, speaking very hypothetically. I still think something is rotten in Denmark.


> Something is rotten in Denmark. If this project achieves a sustained fusion reaction as claimed, that represents a huge breakthrough, and not just for space propulsion, but for the general topic of fusion power.

Achieving fusion in a tokamak or with lasers has been a solved problem for a couple of decades.

The problem with fusion power is generating more energy from the fusion than consumed to power the lasers or tokamak.

There is no such problem here as I understand it; the system isn't supposed to sustain itself from fusion, but instead will rely on solar panels or some other energy source to power the fusion reactor.


> Achieving fusion in a tokamak or with lasers has been a solved problem for a couple of decades.

I should have been more clear -- I mean sustained fusion generation, meaning a net energy gain over that required to start the reaction in the first place. That hasn't been achieved.

> There is no such problem here as I understand it; the system isn't supposed to sustain itself from fusion ...

Not according to the NASA documents (see below). If that were true, there would be no point in using the system. If the fusion reaction produces less power than it requires, the designers would be better off using the source electrical power to drive an ion thruster.

The claim being made is that the fusion scheme creates more power than is required to start it -- by using electrical power to initiate a fusion reaction that produces more power than it requires. If this were not true, the amount of converted solar energy described in the project (i.e. 200 KW) is not enough to propel the relatively massive spacecraft to Mars in 30 days using other methods.

Here's the evidence:

Link: http://www.nasa.gov/directorates/spacetech/niac/2012_phaseII...

Title: "The Fusion Driven Rocket: Nuclear Propulsion through Direct Conversion of Fusion Energy"

Quote: "an in-depth analysis of the rocket design and spacecraft integration as well as mission architectures enabled by the FDR need to be performed. Fulfilling these three elements form the major tasks to be completed in the proposed Phase II study. A subscale, laboratory liner compression test facility will be assembled with sufficient liner kinetic energy (~ 0.5 MJ) to reach fusion breakeven conditions." [emphasis added]

Which brings us back to square one. If this project were to succeed, it would instantly replace the existing approaches (i.e. tokamak and laser inertial confinement) as the most promising candidate for large-scale fusion power generation.

As I said before, something is rotten in Denmark -- why isn't this project being described as a candidate for earthly fusion power generation, given that it must achieve break-even to accomplish its mission?


The thing about a fusion rocket engine is that the energy is used to throw stuff out the back. In a fusion generator this would not be considered a feature - if you want a stationary generator that doesn't melt your city you have to contain that plasma, which is very, very energy-intensive.


Yes, true, but neither scenario has a working model of a fusion generator with power gain > 1.

> if you want a stationary generator that doesn't melt your city you have to contain that plasma, which is very, very energy-intensive.

Actually, if you think about it, a rocket engine that can create a fusion reaction and direct the energy out "the back" as you put it, and a power generator that also directs fusion energy to a secondary process, are very similar. In the extreme case, you could take the space device, put it in a vacuum chamber, and direct the thrust into a steam generator.


  I should have been more clear -- I mean sustained fusion generation, meaning a net energy gain over that required to start the reaction in the first place. That hasn't been achieved.
Yes, it has. Fusion produces energy; the energy you have to put in to initiate fusion does not magically disappear. Thus, if you can do fusion at all, you will end up with more total energy than you started with.

What has not been achieved is capturing enough of that resultant energy in a form (such as electricity) in which it can be used to keep the reaction going. That step, however, is completely irrelevant to a rocket engine. The energy released by fusion is largely kinetic energy, and that is exactly what you want in rocket exhaust, no need to go through a lossy conversion step.

  If the fusion reaction produces less power than it requires, the designers would be better off using the source electrical power to drive an ion thruster.
Not so. If the fusion reaction generates any energy at all, then that is better than just using your electrical power source by itself, for exactly the same reason that it's better to use a starter motor to initiate ignition of gasoline in your car than it is to try to run your car off of a weak starter motor. This is true even if you have no way of using the engine to recharge your battery.

  If this project were to succeed, it would instantly replace the existing approaches (i.e. tokamak and laser inertial confinement) as the most promising candidate for large-scale fusion power generation.
No, it wouldn't. That would only happen if the additional step were taken of discovering a highly efficient means of capturing the kinetic and radiant energy of the engine exhaust and converting it back to electricity. And research into fusion generators that work pretty much like that has been and is being done.

Edit: The slides at http://www.nasa.gov/pdf/636883main_FDR_talk_NIAC_2012_final.... even say:

  It is assumed that initially FDR employs solar panels for house keeping power
  Eventually it would be derived directly from nozzle flux compression
I.e., "once we do figure out how to turn this into a generator, then you don't need solar panels anymore." But they don't know how to derive energy from the exhaust stream through the nozzle yet, so they have to keep it going with solar panels. And extracting energy from the exhaust would necessarily reduce the ISP of the engine somewhat.


>> I should have been more clear -- I mean sustained fusion generation, meaning a net energy gain over that required to start the reaction in the first place. That hasn't been achieved.

> Yes, it has.

No, it has not. Apart from stars and thermonuclear weapons, there are no fusion reactions that yield more energy than they require, i.e. the achieve break-even. It has not happened.

> Thus, if you can do fusion at all, you will end up with more total energy than you started with.

You just changed the subject. Apart from stars and weapons, existing experimental fusion reactions produce much less energy than is required to create them. For example, all the laboratory experiments to date.

Also, very important, in a fusion reactor at less than break-even, the input power must be used to perpetually sustain the reaction (the state of the plasma), so that power is unavailable for any other purpose. Only the fusion reaction's power can be exploited.

So in a hypothetical reactor that requires 1000 watts to sustain fusion but produces 250 watts of fusion power, only the 250 watt fraction is expoitable -- the original power must be reserved for heating the plasma. That's why break-even is essential.

>> If this project were to succeed, it would instantly replace the existing approaches (i.e. tokamak and laser inertial confinement) as the most promising candidate for large-scale fusion power generation.

> No, it wouldn't.

Yes, it would. Given a power gain > 1, it would be child's play to generate steam and spin a turbine, as just one example.

> And research into fusion generators that work pretty much like that has been and is being done.

To date, there have been no -- that's NO -- laboratory fusion generators that produce more power than they require for initiation.


  No, it has not. Apart from stars and thermonuclear weapons, there are no fusion reactions that yield more energy than they require, i.e. the achieve break-even. It has not happened.
That's true, but irrelevant. Producing more energy from the reaction than was required to start the reaction is a different thing from ending up with more total energy in the system than you started with. Even stars don't do that- they just have sufficiently good containment that they don't lose all of the initial ignition energy, and thus don't need additional power inputs to replace non-existent losses.

You seem to be confusing the total power available in a fusion system with the total power available at the output terminals of a generator. The first is relevant to a rocket. The second is not.

To date, energy recovery inefficiencies for fusion reactors have always been high enough that the energy lost to neutrinos / waste heat / etc. is large than the amount produced by the reaction, meaning that the power available at the output terminals is less than the input power. Break-even does not necessarily mean that the reaction itself produces more power than the ignition apparatus- it means that the total useful power you can extract from the system, whether you put it there to begin with or not, is larger than the power required by the ignition apparatus. But a rocket doesn't care about recovery. Any power produced by the fusion reaction counts as a gain.

  So in a hypothetical reactor that requires 1000 watts to sustain fusion but produces 250 watts of fusion power, only the 250 watt fraction is exploitable -- the original power must be reserved for heating the plasma. That's why break-even is essential.
You are implicitly assuming that some of the 250W surplus can be extracted, but that none of the original 1000W can. That's a physically indefensible assumption. If you put in 1000W and the reaction generates 250W, then there's a total of 1250 indistinguishable watts running through the system, and you need to be able to harness at least 1000W to keep the system in steady state. If you can extract more than that, you've got a generator.

  To date, there have been no -- that's NO -- laboratory fusion generators that produce more power than they require for initiation.
I made no claim that there were. I said that research into this kind of fusion generator has been done, not that it has resulted in a working generator yet. See, e.g., focus fusion, or magnetoplasmadynamic generators.


>> No, it has not. Apart from stars and thermonuclear weapons, there are no fusion reactions that yield more energy than they require, i.e. the achieve break-even. It has not happened.

> That's true, but irrelevant.

That's the topic of discussion. Therefore it is relevant.

> Break-even does not necessarily mean that the reaction itself produces more power than the ignition apparatus ...

That is exactly, precisely what it means. That is how break-even is defined.

http://en.wikipedia.org/wiki/Fusion_energy_gain_factor

Quote: "The fusion energy gain factor, usually expressed with the symbol Q, is the ratio of fusion power produced in a nuclear fusion reactor to the power required to maintain the plasma in steady state. The condition of Q = 1 is referred to as breakeven."

Any questions?

> You are implicitly assuming that some of the 250W surplus can be extracted, but that none of the original 1000W can.

I am not implicitly assuming anything. In the example, because 1000 Watts is required to sustain the plasma in a fusing state, none of that power is available for any other purpose -- it might as well not exist. An attempt to harvest any part of that power will extinguish the fusion reaction. This leaves 250 watts. Those are the facts.

> That's a physically indefensible assumption.

Okay, you need to learn basic physics. One cannot harvest more than 250 watts from the hypothetical system without extinguishing the reaction. The original 1000 watts is unavailable -- it might as well not exist.

>> To date, there have been no -- that's NO -- laboratory fusion generators that produce more power than they require for initiation.

> I made no claim that there were.

Yes, you did. That was your claim -- that fusion reactors produced more power than they required for initiation. Here's what you said:

> Thus, if you can do fusion at all, you will end up with more total energy than you started with.

It is false. While the reaction is underway, you do not have more total energy than you started with, you have less. I have explained why this is so, very clearly.


You simply are not even reading. Nobody said anything about maintaining any steady state. That's needed for a generator. This project is talking about doing one off detonations.

Have you heard of a hydrogen bomb? If they lost energy to creating the fusion in a hydrogen bomb, what would be the point? If you removed the fusion part of a hydrogen bomb, would you get a bigger explosion? No. You get MORE ENERGY using fusion. However, we don't have a way to harness that to make electricity yet to maintain a steady reaction. But maintaining a steady reaction is not what this project proposes doing. Do you get it yet?

Edit: smaller explosion -> bigger explosion. So many explosions.


> You simply are not even reading.

And your evidence is that I quoted everything that I replied to, word for word, and quoted from the original NASA project documents as well?

> Nobody said anything about maintaining any steady state.

I did, and so did NASA. You missed its significance. Pulsed systems have an average power level, and a peak power level. Both need to be analyzed.

> That's needed for a generator.

Yes, and NASA wants a net generator of energy, something better than break-even, otherwise it's not worth doing. And they say this in their documents about the project.

> This project is talking about doing one off detonations.

I can't believe you missed the significance of NASA'a remarks about break-even. Don't you understand that, pulsed or not, break-even still has a meaning, and if they can't get to break-even, the project makes no sense?

A steady state generator either does or doesn't achieve break-even. A generator that consists of a series of pulses also does or doesn't achieve break-even. Here's what NASA has to say about this:

http://www.nasa.gov/directorates/spacetech/niac/2012_phaseII...

Quote: "A subscale, laboratory liner compression test facility will be assembled with sufficient liner kinetic energy (~ 0.5 MJ) to reach fusion breakeven conditions."

I can't believe NASA thinks break-even is an essential program goal. Maybe they should hire you as a consultant, so they won't waste taxpayer dollars trying for break-even, after all, according to you, because the output is pulsed, break-even has no meaning.

> But maintaining a steady reaction is not what this project proposes doing.

You very clearly do not understand the relationship between peak and average power. The device being described generates a series of pulses, but for there to be a point to the exercise, the average output power must exceed break-even.

A radar has a peak output power of two megawatts and a steady-state input power of ten watts. Does the radar violate the principle of energy conservation? Yes or no?

A fusion reactor has a peak output power of two megawatts and requires an average plasma sustaining power of 200 KW. Such a generator either does or does not achieve break-even over time, and as quoted above, NASA cares very much which is so.

> But maintaining a steady reaction is not what this project proposes doing.

You need to learn the relationship between peak and average power. Stop embarrassing yourself.

http://www.radartutorial.eu/18.explanations/ex28.en.html

http://hank.uoregon.edu/experiments/modelocked-fiberlaser/20...

> Do you get it yet?

You have managed to miss every key fact about this project.


I guess the point is less about the fusion method being efficient (and getting past break-even) but more about propulsion. ie. for 200KW of input do you get more propulsion from initiating a fusion reaction than using an ion ejection method.

Their aim is to move a heavy object with as little fuel as possible not necessarily produce perfect fusion. (although obviously that would be nice for everyone!)


> I guess the point is less about the fusion method being efficient (and getting past break-even) but more about propulsion.

But "break-even" means yielding more energy than is required to start the reaction. Obviously anything less than break-even is not worth having -- a chemical rocket would be more efficient.

> Their aim is to move a heavy object with as little fuel as possible not necessarily produce perfect fusion.

This misses the point that present laboratory fusion reactions require more power than they release. It's not a question of "perfect fusion" but any fusion that has a net positive energy yield.


> Obviously anything less than break-even is not worth having

No. Not at all. We are talking propulsion, using fusion reactions to pass on energy to the propellant and convert that into thrust. Although it would be desirable, it's not required to make it a net-positive reaction - just giving the propellant more energy than a chemical reaction is enough to be more efficient than a chemical rocket.

As the article mentioned, you can power this rocket with an ISS worth of solar panels (which is quite a lot of mass). Or, as it didn't mention, a very small fission reactor (provided you could negotiate putting a 200 KW reactor in space).


>> Obviously anything less than break-even is not worth having

> No. Not at all.

Yes -- if the fusion reactor didn't achieve break-even, the designers would be better off using an ion thruster. Also, the NASA documents that describe the project assume that break-even must be achieved:

http://www.nasa.gov/directorates/spacetech/niac/2012_phaseII...

Quote: "an in-depth analysis of the rocket design and spacecraft integration as well as mission architectures enabled by the FDR need to be performed. Fulfilling these three elements form the major tasks to be completed in the proposed Phase II study. A subscale, laboratory liner compression test facility will be assembled with sufficient liner kinetic energy (~ 0.5 MJ) to reach fusion breakeven conditions."

They are talking about doing away with the present lines of fusion research, which haven't achieved break-even, and using a different method. But they don't suggest that this, or some variation, might be used for conventional power generation.

> Although it would be desirable, it's not required to make it a net-positive reaction

Yes, it is -- that is required. Were this not true, the designers would be better off using an ion thruster, which already exists and is quite efficient.

> As the article mentioned, you can power this rocket with an ISS worth of solar panels ...

Yes, that's in the description, but the power available (200KW near earth, 100KW near Mars) is not enough to propel the relatively heavy craft to the mission profile (i.e. 30 days to Mars) without some other source of energy, like from a net fusion power gain > 1.


A rocket only needs to achieve thermal break-even. A power plant needs to achieve electrical break-even, which includes the unavoidable loss from converting the heat to electricity in a heat engine.

In this way a system can be simultaneously useful for space travel but useless for power generation.


> A rocket only needs to achieve thermal break-even. A power plant needs to achieve electrical break-even ...

Yes, all true. But if a fusion reactor ever achieved break-even, that would be such a breakthrough that the specifics would be reduced to footnotes, and both thermal and electrical applications would soon follow.

> In this way a system can be simultaneously useful for space travel but useless for power generation.

My point is that if break-even were to be achieved, it would be break-even for both applications. The reason is that the plasma conditions for fusion break-even would have much more in common in the two cases than the differences.


If fusion doesn't provide a substantial energy gain, it's not worth the effort. Existing ion thrusters are quite efficient (60+%) at translating electrical power to exhaust kinetic energy.


Indeed, but they offer very low thrust. For manned space travel, you may need something that can give you a higher acceleration, even if at the expense of efficiency.

Also, fusion reactors designed for power generation have very different goals than fusion rockets. With power generation, particles leaving the reactor may be considered wasted energy. With rockets, the whole idea is to have particles leaving the reactor in a certain direction taking as much energy as possible with them. You just point the jet at the direction opposite to the one you want to go.


Well, controlled fusion hasn't reached energy breakeven at all, even taking into account the kinetic energy of the reaction products. But the low thrust of current ion engines is mostly due to power restrictions (https://groups.google.com/group/sci.space.science/msg/0cb332...). If your spaceship has a mass of one ton and you want an acceleration of 1 centigee with an exhaust velocity of 30 km/s, you will need at least:

0.5 * thrust * velocity = 0.5 * (0.1 m/s^2 * 1000 kg) * 30 km/s = 0.5 * 100 N * 3E4 m/s = 150E4 W = 1.5 MW

of power.


"kinetic energy" means nothing alone, thrust and specific impulse are better metrics to look at. Doing a lot better than ion thrusters at either without being too much worse in the other and energy efficiency would be interesting.

However, the article quotes an exhaust velocity of 30km/s (or ISP of 3000s), and using 200kW doesn't leave much room to beat http://en.wikipedia.org/wiki/HiPEP on thrust without counting on net energy gain. The linked slides also claim net energy gain.


Yes, I agree. My point was that you cannot do substantially better than ion engines without having energy gain and, in fact, you are probably going to do much worse due to the weight of the "fusion hardware".

I'm quite optimistic about magnetized inertial fusion. But the idea of doing the job much better than the Z-machine, with something lightweight enough to carry into space and in less than 10 years seems to me... unlikely, to put it mildly.


>in fact, you are probably going to do much worse due to the weight of the "fusion hardware".

Ion engines have weight, too. What leads you to believe that the fusion hardware will be heavier?


In the short run:

- Ion thrusters are way simpler and they are trying to do something that is much easier.

- Ion thrusters are relatively mature, working "fusors" don't exist.

- Existing machines that are trying to get fusion breakeven are building-sized.

- Trying to start a fusion reaction is hard, it only makes sense if you get a commensurate result (energy gain).

In the long run, I'm very optimistic about fusion.


Ion drives are highly efficient, but have ridiculously low thrust. Which doesn't help at all when you are trying to reach some point quickly.

If you can construct an ion drive with enough thrust to match this proposed fusion drive (or even a NERVA: http://en.wikipedia.org/wiki/Nuclear_thermal_rocket), talk to NASA, I am sure they will be interested in buying several from you.


> Which doesn't help at all when you are trying to reach some point quickly.

Sure it does. You just leave it turned on. This thruster assumes 6 days of thrust then 24 days of coasting. With an ion thruster you leave it on for all 30 days.

There are no high thrust systems that can just be left on - even nuclear ones are used for a short period then turned off. The idea of an ion thruster is that you leave them on, and achieve the same total thrust, over the same time.


> With an ion thruster you leave it on for all 30 days.

With a thrust of - at best - 5 newtons, you won't achieve the goal of getting to Mars faster. You may get there cheaper and using less fuel, but for pure speed you lose. Ion thrusters are good for very long trips when you're going to leave the engine on for months, or for trips where the total time doesn't matter much, only fuel economy (e.g. for cargo shipments or probes).


5 newtons won't get you there in 1 month, but according to http://en.wikipedia.org/wiki/VASIMR it will in 5 months which is still pretty good, and much better than a standard rocket.


If you don't mind waiting a year.

Existing ion thrusters don't give enough thrust to get to Mars in 30 days.


You are completely missing a point of this. It is a propulsion system, not a power generating one. Chemical rocket engine doesn't generate any electrical power either. Main factors in propulsion is specific impulse and reaction mass and this idea promises a huge impulse - basically once in orbit, it could ferry between Earth and anywhere-where-solar-power-is-sufficient because it doesn't need tonnes of fuel, only relatively small load of pellets would get the job done. Of course there is the issue of getting it and it's payload into orbit, but I'd say Skylon will take care of that


> You are completely missing a point of this. It is a propulsion system, not a power generating one.

To represent an advantage over an ion thruster, it must be both. And the NASA documents that describe the project specify a fusion power gain > 1:

http://www.nasa.gov/directorates/spacetech/niac/2012_phaseII...

Quote: "an in-depth analysis of the rocket design and spacecraft integration as well as mission architectures enabled by the FDR need to be performed. Fulfilling these three elements form the major tasks to be completed in the proposed Phase II study. A subscale, laboratory liner compression test facility will be assembled with sufficient liner kinetic energy (~ 0.5 MJ) to reach fusion breakeven conditions."

The phrase "fusion breakeven conditions" means the reaction must produce more power than is requires to start it. This is a requirement to justify the project over other approaches.


It is not even supposed to be used to generate electrical power. Citing from the site itself: "Virtually all of the radiant, neutron and particle energy from the plasma is absorbed by the encapsulating, metal blanket thereby isolating the spacecraft from the fusion process and eliminating the need for large radiator mass"

No radiators implicitly mean no electricity generation, because it creates waste heat that has to be utilised.

http://en.wikipedia.org/wiki/Fusion_rocket

Proposed concept is a direct drive, and it actually claims they fixed the problem with neutrons (they are caught by the compressing metal)

As for breakeven conditions they merely state that the power that the fusion generates must be at least equal to power used to start/sustain it. http://en.wikipedia.org/wiki/Fusion_energy_gain_factor Theoretical limits of efficiency of heat engine is around 70-80% (roughly) http://en.wikipedia.org/wiki/Thermal_efficiency and you have to use those to convert heat generated in controlled fusion into electricity. To actually achieve net power generation in a power plant, you have to generate a lot more heat that electricity, while for propulsion you merely care about actual raw (so to speak) power.

Ion thrusters have their own issues, while their ISP is considerably better than chemical rockets, maximum thrust is abysmal, but it is hard to argue about that due to the lack of data on FDR. However, with ion thrusters there are other issues (for example:wear, charge imbalance)


> As for breakeven conditions they merely state that the power that the fusion generates must be at least equal to power used to start/sustain it.

Yes, but (apart from stars and weapons) this has never been achieved anywhere, ever. This is a big issue, bigger than most people realize.

https://en.wikipedia.org/wiki/Fusion_power

Quote: "As of July 2010, the largest experiment by means of magnetic confinement has been the Joint European Torus (JET). In 1997, JET produced a peak of 16.1 megawatts (21,600 hp) of fusion power (65% of input power) ... Fusion powered electricity generation was initially believed to be readily achievable, as fission power had been. However, the extreme requirements for continuous reactions and plasma containment led to projections being extended by several decades. In 2010, more than 60 years after the first attempts, commercial power production was still believed to be unlikely before 2050."

My point is if this project creates a net gain > 1, it will address a lot more than the problem of getting to Mars.


As other posters have noted, ion thrusters don't generate very much thrust.


s/Skylon/SpaceX/


That's what I was thinking. They're actually already doing something. On the other hand, their not-yet-developed Falcon Heavy can "only" lift 53 tons, about a third of the weight of FDR. Hopefully they can come up with a way to lift it in stages, or we still need a bigger rocket.


> Obviously anything less than break-even is not worth having -- a chemical rocket would be more efficient.

Why not? The energy to start the reactor comes from solar power, so they didn't have to carry it up with them.


It's not a sustained reaction. It's just a bunch of short fusion reactions, one after another. We've been capable of short, uncontrolled fusion reactions for decades--it's just that, being bombs, we didn't have much luck generating electricity from them. A hydrogen bomb uses a relatively small quantity of conventional explosives to start a reaction which ultimately releases orders of magnitude more energy than the original input. This engine claims to use a small input of electrical energy to trigger a reaction which releases a lot of energy. Then, much like a car getting blown off the road by a nuclear test, they just position their ship near this reaction and get shoved away.

The proposal specifically says they will not convert the energy to electricity, but will use the reaction directly for thrust.


Actually hydrogen bombs don't use conventional explosives. They use fission. See http://en.wikipedia.org/wiki/Pure_fusion_weapon (a hypothetical bomb).


> Actually hydrogen bombs don't use conventional explosives. They use fission.

Sort of, but because the fission trigger requires conventional explosives, one could argue that conventional explosives play a key role.

In temporal sequence:

1. Conventional explosives compress the fission core.

2. At maximum compression, a special neutron source releases a burst of neutrons to start nuclear fission.

3. The fission trigger delivers a huge pulse of energy to the mixed hydrogen isotope / fission secondary, compressing and heating it.

4. The secondary begins to fuse, releasing much more energy than the fission trigger could produce on its own.

The above is somewhat oversimplified:

http://en.wikipedia.org/wiki/Thermonuclear_weapon

It's our weak imitation of a star.


The same guy (John Slough) started Helion Energy, which is attempting to build a power-producing fusion reactor. Last I heard they had a 1/3 scale device with promising results, and needed $20 million for a full-scale test. But he got funding for the rocket first.

The rocket project may actually be easier. It only pulses once per minute, just runs for three days, and doesn't have to deal with the economic considerations of a practical power plant.

Incidentally, Helion is not the only alternative fusion project in the works. Others include Sandia's MagLIF, Lockheed's recently-announced project, Tri-Alpha, General Fusion, Focus Fusion, and IEC/polywell.


> Last I heard they had a 1/3 scale device with promising results, and needed $20 million for a full-scale test.

Research takes time, the potential payoff is huge, but in the final analysis, the fusion reaction has to produce more power than it requires. It has to achieve what's called "break-even".

A fusion reaction with a power gain < 1 is endothermic -- its temperature is less than that of its power source. A fusion generator by definition produces more power than it requires for initiation -- it has a power gain > 1, and it is exothermic.

> Incidentally, Helion is not the only alternative fusion project in the works. Others include Sandia's MagLIF, Lockheed's recently-announced project, Tri-Alpha, General Fusion, Focus Fusion, and IEC/polywell.

This is a good example of long-shot science, applied research. None of these ideas show very much promise, but the potential payoff is so big that (IMHO) the research money is well-spent.


>A fusion reaction with a power gain < 1 is endothermic -- its temperature is less than that of its power source.

You are trolling! Or you just don't get it. The energy does not disappear. If you put in 1, and the reaction gives you .5, you have 1.5. You do not have to maintain a stable reaction, in the same way a hydrogen bomb doesn't have to produce however many terajoules of electrical energy to be more useful than TNT. It just has to be more total.

They are not making an electric generator, they are making a rocket. They are not the same thing.


> The energy does not disappear.

Below break-even, the source power is requires to sustain the plasma in a high-energy state to maintain fusion. Therefore it's unavailable. Any effort to extract more power than the fusion reaction produces will extinguish the reaction.

Example -- let's say we have a fusion reactor that doesn't achieve break-even (example: all existing laboratory reactors). Let's say very hypothetically that heating the plasma sufficiently requires 1000 watts (sometime in the future) but the fusion reaction itself only produces 250 watts.

Once the fusion reaction has been established, we can only extract 250 watts from the system. Any effort to extract more will extinguish the reaction. Therefore more power must flow into the system than can be taken out. It's endothermic.

Which word didn't you understand?

> If you put in 1, and the reaction gives you .5, you have 1.5.

You, too, can learn the physics required to understand this system. You just have to think a bit harder.

> You do not have to maintain a stable reaction

On average, yes, you do. This project has a peak and an average power that differ greatly, but terms like break-even still have their normal meaning, which is why NASA mentions break-even in the project's documents as a required project goal.

http://www.nasa.gov/directorates/spacetech/niac/2012_phaseII...

Quote: "A subscale, laboratory liner compression test facility will be assembled with sufficient liner kinetic energy (~ 0.5 MJ) to reach fusion breakeven conditions."

What does break-even mean in a pulsed fusion generator? It means the average output power is greater than the average input power.

> They are not making an electric generator, they are making a rocket. They are not the same thing.

Yes, they are the same thing. They both require break-even, and they both rely on a fusion reaction.

> You are trolling!

I know this subject, you do not. Therefore it is you who are trolling when you should be reading.


> Which word didn't you understand?

I understood all of it, I just think you're wrong. And unless you ever address what anyone is saying, all I can do is keep on thinking you're wrong.

Nobody - nobody here, nobody on TFA - said anything about sustaining a reaction. It is a one-off explosion much like a weapon. An explosion like that is hard to use for generating electricity, just like a bomb, but great for pushing things around. Why isn't this feasible? Please explain. Why can we detonate a hydrogen fusion bomb, which generates a lot of energy (but no electricity), but we cannot initiate a tiny short term burst with a carefully designed fuel pellet?

I'm not saying they have everything figured out. I'm just saying I wouldn't be so skeptical to think it would be some amazing breakthrough if they do it. If this rocket works, we still don't have usable fusion electricity. That problem still needs to be solved. But it is not the same problem.

> Yes, they are the same thing. They both require break-even

No, electrical generation means you need to need to somehow use your energy to heat up something and turn a turbine, or something like that. Which means you need some kind of ongoing stable and contained reaction. There are so many difficulties with that, it really WOULD be a big deal if they solved that problem. Just making a small explosion? Not as far fetched.

> I know this subject, you do not.

And don't try to argument-from-authority me. You're a random account on the internet just like me. As far as I know you're some crackpot pseudoscience crazy. Not that I believe that, but I don't know better.


It's not continuous, it's pulses. But that doesn't actually matter, attach this thing to a big wheel and pulse it to run a generator. Or a few of them pulsing in sequence.

But I wonder if the radiation exhaust might be to high to be practical on earth.


The fusion products are presumably fairly hot - so why not use them to heat water and drive a steam turbine generator combination?

[NB This is in reply to the idea of using whirling fusion generators as a means of generating power, not part of the discussion on using it as spacecraft propulsion!]


I think the suggestion is that the fusion is achieved only around the tiny pellet, and that the fusion acts against the magnetic containment to actually propel the pellet out the back. That's my guess - which slightly beats the idea they have achieved sustainable net positive energy fusion but cannot be bothered to solve all the worlds energy problems and become trillionaires.


If this idea had been reduced to practice, it would mean the end of the National Ignition Facility, which after decades of effort, has yet to produce more power than is required to start the reaction:

http://en.wikipedia.org/wiki/National_Ignition_Facility

If the described method actually worked, it would force a complete reevaluation of the other approaches to fusion, none of which have actually worked (in a practical sense) after decades of effort.

That's why I doubt that the described method has moved beyond the theoretical phase. If this isn't true, then people would try to create a continuous-power version of the technology, in which prior energy releases and high temperatures would be used to sustain new fusion energy releases.

I've been reading about fusion power research for decades, I know the problems, and I remain skeptical.


It's actually surprisingly difficult to capture the heat energy.

The energy is released as neutrons, neutrinos and gamma rays, all of which tend to escape rather than heat the surrounding area.

But all of them are magnetically neutral, so I wonder how they propose to capture their momentum.


Also speaking very hypothetically, why do you suppose that all the input electrical power is wasted for the propulsion goal? Each fusion mini-explosion will have a total energy that is the sum of the input (ignition) energy and the fusion itself, not just that of the fusion.

Edit: This would mean that the thrust could be higher than the electrical input power even below break-even for the controlled fusion. If you only consider the electrical input, you could have a >1 ratio for the electrical energy/kinetic energy conversion (thanks to the fusion).


> Also speaking very hypothetically, why do you suppose that all the input electrical power is wasted for the propulsion goal? Each fusion mini-explosion will have a total energy that is the sum of the input (ignition) energy and the fusion itself, not just that of the fusion.

Yes, technically true, but consider this hypothetical scenario:

1. A power source, let's say 1000 watts, can be used for any purpose, or can be used to heat a fusion plasma.

2. A fusion reactor requires 1000 watts to sustain fusion but delivers 250 watts of fusion power.

3. The total power in the system is now 1,250 watts.

4. But that total power is not available for external uses. 1000 watts of it must perpetually be applied only to the task of heating the plasma.

5. That leaves 250 watts for other uses.

That means the fusion reaction uses more power than it produces, only 250 watts is available for other purposes, and there is no remedy except to not use the fusion reactor.

That's why break-even is an essential precondition for this project's viability.


"It's very scalable; we can achieve fusion at a much smaller scale," he said. "We could run the designed engine off 200KW of solar panels, which is about the same power as generated by the panels around the International Space Station"

So this is hot fusion, not cold. Hot fusion has been around for a long time. In fact I remember a couple of high school kids made a hot fusion device once.


My understanding is that "hot" fusion is actually fairly easy - it's generating a surplus of energy from fusion[*] outside of a nuclear weapon that is the tricky part.

http://en.wikipedia.org/wiki/Fusor

[Note: Typically in most H-bomb designs most of the energy still comes from fission - the fast neutrons from the fusion in the secondary igniting fission of the DU tamper round the secondary].


> My understanding is that "hot" fusion is actually fairly easy ...

Unless you're talking about a thermonuclear weapon, it's not easy at all. In fact, decades of research have yet to produce a break-even reaction in the laboratory.


I think you needed to read the second half of that sentence before replying.


> Hot fusion has been around for a long time.

Only in the stars and in thermonuclear weapons. It has not been achieved in a break-even sense anywhere else, in spite of decades of research. Many very large projects are dedicated to achieving it, including the National Ignotion Facility:

http://en.wikipedia.org/wiki/National_Ignition_Facility

The linked article shows that, in spite of vast amounts of money being spent, the project has yet to achieve break-even (i.e. produce more power than required to start the reaction).

> In fact I remember a couple of high school kids made a hot fusion device once.

No, that did not happen. It's an urban myth.



This is just a plasma generator, not a fusion reactor. Not to dismiss this student's achievements, but any fluorescent lamp is a plasma source. Plasma is the "fourth state of matter", essentially separate electrons and nuclei in a relatively high energy, electrically conductive medium:

https://en.wikipedia.org/wiki/Plasma_(physics)


It's a fusor - which does (as its name suggests) do fusion - which is why they are used as neutron sources.

http://en.wikipedia.org/wiki/Fusor


A quote from your linked article: "Hopes at the time were high that it could be quickly developed into a practical source of fusion power. However, as with other fusion experiments, development into a generator has proven to be difficult."

Translation: no break-even fusion reaction. If this approach held promise for fusion power research, it would be being explored instead of the millions of dollars in the much more common laser-confinement and tokamak approaches.

Strictly speaking and from a technical standpoint, if it doesn't produce more power than is present for conventional reasons (like electronic current flow), and in spite of its name, it's not a fusion reactor as that term is understood in physics.

It's a nice plasma source, and it produces neutrons -- very useful -- but it's not a fusion power source.


I never said it was a "reactor", or that it was close to break even - merely that creating a device where fusion reactions do occur is not that difficult.

Read my comment above I say "Nowhere near break even though."

Incidentally, there has been a lot of work in inertial electrostatic confinement - it doesn't look terribly promising and no it is not break even but people do appear to be working in this area:

http://en.wikipedia.org/wiki/Polywell


As established by arethuza, hot fusion has been accomplished for some time, relatively easily, outside of thermonuclear weapons and stars. That was the claim in dispute. Nowhere in this thread was there a claim about power generation.


> As established by arethuza, hot fusion has been accomplished for some time ...

Let's be clear about what we're talking about. A fusion generator by definition produces more power than it requires. Apart from stars and thermonuclear devices, this has not been achieved anywhere. Without clear terminology, we will go in circles.

Also, the NASA project documents specify and require a net power gain in the fusion reaction:

http://www.nasa.gov/directorates/spacetech/niac/2012_phaseII...

Quote: "an in-depth analysis of the rocket design and spacecraft integration as well as mission architectures enabled by the FDR need to be performed. Fulfilling these three elements form the major tasks to be completed in the proposed Phase II study. A subscale, laboratory liner compression test facility will be assembled with sufficient liner kinetic energy (~ 0.5 MJ) to reach fusion breakeven conditions."

> Nowhere in this thread was there a claim about power generation.

Except in the NASA documents that describe the project under discussion.


Yea. That is what is called hot fusion - where you have to put in energy to keep the fusion going.

And yes I was referring to the Fusor linked below. That is hot fusion.


> That is what is called hot fusion - where you have to put in energy to keep the fusion going.

No -- in general, "hot fusion" means producing more power than is required to start the reaction. Otherwise the term "hot fusion" makes no sense, since a reaction with a power gain < 1 is endothermic.

I emphasize that the term "hot fusion" is used in a lot of different ways, by people who aren't using it in its strict physical meaning. But in physics, "hot fusion" should mean an exothermic fusion reaction.

> And yes I was referring to the Fusor linked below. That is hot fusion.

It's not a fusion generator, which by definition produces more power than it requires. And the NASA documents that describe the project under discussion specify a fusion generator, a device with a power gain > 1.

http://www.nasa.gov/directorates/spacetech/niac/2012_phaseII...

"an in-depth analysis of the rocket design and spacecraft integration as well as mission architectures enabled by the FDR need to be performed. Fulfilling these three elements form the major tasks to be completed in the proposed Phase II study. A subscale, laboratory liner compression test facility will be assembled with sufficient liner kinetic energy (~ 0.5 MJ) to reach fusion breakeven conditions."

Note that last few words.


it's not about having net energy gain, it's about converting electrical and nuclear energy into kinetic energy.


> it's not about having net energy gain ...

That's not what the NASA documents say, the documents that describe the project:

http://www.nasa.gov/directorates/spacetech/niac/2012_phaseII...

Quote: "an in-depth analysis of the rocket design and spacecraft integration as well as mission architectures enabled by the FDR need to be performed. Fulfilling these three elements form the major tasks to be completed in the proposed Phase II study. A subscale, laboratory liner compression test facility will be assembled with sufficient liner kinetic energy (~ 0.5 MJ) to reach fusion breakeven conditions." {emphasis added]

Without a net energy gain, the project would be better off using an ion thruster, which has the advantage of already existing and being quite efficient (but with a power gain < 1).


To repeat what others have told you several times in this thread:

Why do we still use chemical rockets instead of ion thrusters for boosters? Answer: thrust vs. specific impulse. Ion-thrusters are efficient in use of (high specific impulse), but are weak in how much thrust they create. Your ship would have to be mostly ion-thruster to get it anywhere, thus ruining the efficiency advantage with respect to payload of the engine.

http://en.wikipedia.org/wiki/Ion_thruster "Given the practical weight of suitable power sources, the accelerations given by ion thrusters are frequently less than one thousandth of standard gravity."

What does linear kinetic energy have to do with fission reactors? It's not as simple as "attach a turbine to the kinetic energy conversion process." Or rather, it is that simple, and that's why it doesn't work, because it's another point at which one loses power to inefficiency. But if all you want is kinetic energy in the first place, then you don't lose efficiency to that extra step.


There is something you are not getting. Assuming a set of solar panels like those on the ISS, able to deliver 200KW near Earth and 100KW near Mars, one must still convert that power to useful thrust. That means achieving fusion break-even, a requirement that the NASA documents explain.

Obviously ion thrusters aren't practical for this kind of heavy lifting and short mission time, but that doesn't usher in fusion power as an obvious substitute -- unless the project creates a useful reaction, meaning a gain > 1.


Hmm, a little goggling gives a hint this may not be BS after all.

I am unclear on the exact methods, but there appears to be existing research into generating a plasma "pinch" via compression of aluminium around a core of detrinium-tritium. This generates a massive magnetic-flux (which seems to be a result of actual fusion during the compression) and if it is held in a magnetic cage with an out at the back, you have propulsion.

(1) http://en.wikipedia.org/wiki/Pinch_(plasma_physics) (2)http://en.wikipedia.org/wiki/Explosively_pumped_flux_compres... http://en.wikipedia.org/wiki/Explosively_pumped_flux_compres...


Love to watch (and support with my money) all these low cost space propulsion projects. This kickstarter project http://www.kickstarter.com/projects/2027072188/plasma-jet-el... was particularly amazing to watch. Best donation / entertainment money spent ever. And I hope B612 foundation would result in some great fun as well ;) Or not :)

And another thing. And advice for kids looking for summer internships. Don't do these 'iPhone games' startups. Try something real, like NASA or Lockheed, or whatever. If you good, who knows, maybe a few lines of your code will have a chance flying into space.


Former aerospace, current iPhone app guy here. Each career path has its pros & cons. Working at a place like NASA or Lockheed lets you work on some very cool projects, often times you are working on some project that never sees the light of day (canceled due to budget cuts and what not). Also, the bureaucracy at large aerospace organizations can be stifling.

Having said that, Space X seems like it offers the best of both worlds.


I should have been slightly more precise, the advice was specifically about taking an internship in aerospace as a kid. I don't have any advice about having a career in aerospace industry... Haven't had one. I only had a short internship as a high school student at aero/space R&D company back in Russia. But that [aero/space R&D, not Russia ;)], I can highly recommend.

I think actually, a more general advice is to take an internship in any high tech industry area in which a cost of software or design failures is very, very high.


From the article: Given the tight financial strictures of the US government this is unlikely

This is what pisses me off about the last decade. Plenty of money to bail out the richest people the planet has ever seen. Plenty of money to kill brown people. Making a fusion drive? Making sure we all have medicine? Sheesh, we're not made of money!


The FDR is one of only ten projects to get Stage Two funding from the program. This $600,000 award will provide the proof-of-concept FDR system over the next 18 months, and a working spacecraft would be ready as soon as 2020, Pancokti predicted – but if NASA wanted to throw money at the project, this timescale could be cut.

There's a lot of people on HN who could double that budget without blinking, he hinted.


Reading lutusp post, anyone on HN who got sufficient funds to double the budget, would also have learnt to look very closely at extraordinary claims with only ordinary evidence.

Be nice if it was true, and one day I am sure it will be (I mean the Sun DES this all the time and not even a single Phd was involved)


I'm not saying this FDR is guaranteed to work or be the best idea, but I'm pretty sure lutusp is trolling or something. He is clearly not understanding any of the issues. Repeatedly he talks of needing to create a steady reaction, and talks about needing to meet the same requirements of a fusion electric generator. Neither of these things is proposed by the FDR project. It is pulsed, and it generates only kinetic energy (much like an H-bomb, relatively old and proven technology). Further, he talks of ion thrusters as an alternative, which would take months to get to Mars, whereas this is talking about 30 days.


The once a minute firing of the engines feels like it'd be a very unpleasant sensation - I wonder what the momentary acceleration experienced would be.

Also - this craft sounds perfectly suited for laser-transmitted power (rather than carrying a large solar array) - have one or more earth-orbiting lasers beaming energy to the craft. Though I'm not sure if we have the technology today to aim & focus a laser at that range (?)


I saw George Dyson give a talk about the Orion project - where they were planning to set off conventional atomic bombs in a series to propel spacecraft - and he had found a paper that had done the math and claimed that the crew of the spacecraft would only feel low-frequency sound, like the bass at a loud rock concert.


What kind of residues leaves that kind of engine? is it gas or solid? because small solids at that speed will surely make the earth orbit in a quite dangerous shooting range in no time. What is the expected coherence of a gas cloud flying that fast? Is it going to be dangerous? or will simply dissolve in to space. Would the material expelled fly away from earth orbit?. Sorry, too many questions..


My guess would be that the products would be gases. Pinching a little ball of deteurium would make it very hot, and vaporise the metal that squishes it.


Are gases dangerous at 30km/sec?. I mean, of course they are, but are they still dangerous in space?. Will the cloud keep more or less cohesive or will it disperse?


It will disperse. Gas is made up of atoms going in many different different directions; even if some gas doesn't seem to be moving that's just a statistical average.

Thus, in space all those different particles will fly off in different directions at 30km/sec. They'll be harmless in microseconds.


Even if it was solid, it's moving at 30 km/s - it won't stay in earth orbit - it won't even stay in solar orbit.

But it's not a solar - way way too hot. It's a gas, mainly helium, and it's highly charged so it will just join the solar wind (which is moving at 400km/s).


This is very early, preliminary research. Actual fruits of a manned or otherwise fusion rocket to Mars may be decades ahead. Even at NASA's slow pace they could get there by the 2030es (or 2020es if they listen to Zubrin).

Edit: at 150 tons payload for low orbit (early estimate) it's not exactly easy to launch. If you can do that on a man-rated rocket you're all ready for Mars on just chemical propulsion (in a Mars-direct/Mars-semidirect scenario).


Not even the Saturn V could launch 150 tons into LEO (though it could come close). No current rocket even comes close.


Columbus took almost one month to pass through the Atlantic Ocean, who could imagine something like this even one century ago?


Maybe I misunderstand everything, but why couldn't such a system be use on Earth as fusion power plant? (it seems to produce more energy than is consumed to produce the fuel, right?)


> Maybe I misunderstand everything, but why couldn't such a system be use on Earth as fusion power plant?

That was my question also (see my other post in this thread) -- if they really achieve fusion break-even (i.e. produce more power than they require to start the reaction) then they have done something that many decades of fusion research have so far failed to achieve. If their device can really do what they claim, it has implications far beyond the described project.


I am not validating these sources but suggest that there is a known approach that collapses aluminium over a core deuterium tritium. It is not self sustaining, but it generates some net positive energy, thus enough I guess to throw a pellet out the door

http://www.alternative-energy-action-now.com/general-fusion....


If this method actually worked, I think we would all know by now. Achieving break-even in a controlled laboratory fusion reaction is the "holy grail" of fusion research and would produce instant worldwide headlines, not unlike the (ultimately false) claims made by Pons & Fleischmann, who thought they had achieved room-temperature fusion some time ago:

http://en.wikipedia.org/wiki/Cold_fusion

So I don't think so. It's a matter of how much a positive result would completely change the fusion research landscape. It's something that people would know about right away.


You insist on a misnomer. Achieving electrical breakeven haven't been done yet (and even if it will be)


Sorry, this site really doesn't like pinch to zoom. I'm having a little trouble - the post wasn't even supposed to be posted, but oh well.

I was doing research and apparently I was wrong too, depending on a definition of fusion breakeven (which I was unable to find) Care to explain what is yours?

If you achieve even smallest amount of fusion, technically you have more energy than you started with. Electrical break even would be the holy grail of fusion research, but even then you have to reach economic feasibility (produce enough power to pay back the cost of a plant)


> I was doing research and apparently I was wrong too, depending on a definition of fusion breakeven (which I was unable to find) Care to explain what is yours?

Fusion break-even means the reaction produces more than or equal to the power required to initiate it. Apart from stars and weapons, it has never been achieved.

http://en.wikipedia.org/wiki/Fusion_energy_gain_factor

Quote: "The fusion energy gain factor, usually expressed with the symbol Q, is the ratio of fusion power produced in a nuclear fusion reactor to the power required to maintain the plasma in steady state. The condition of Q = 1 is referred to as breakeven."

> If you achieve even smallest amount of fusion, technically you have more energy than you started with.

Yes, but with serious problems. One of them is that you have to continue providing more power than the reaction creates, in order to keep the reaction going. This means the overall available power is less than the input power. The reaction is using up much of the power to sustain itself, and that power can't be applied to another purpose. So even though technically there is a lot of power present, it cannot be applied to any purpose other than energizing the plasma. This means the net available power is less than the input power.

This is a bit hard to visualize, so let's say that we have 1000 watts available to apply to some ordinary purpose, or to sustain a fusion reaction.

We discover that the fusion reactor requires all 1000 watts to keep its plasma activated and fusing, but the fusion reaction only produces 250 watts. So, even though there is 1,250 watts of power in the system, 1000 watts of that is required to sustain the plasma in its fusing state and is therefore unavailable. That means only 250 watts is available for any other purpose.

Hence the importance of break-even. :)


> You insist on a misnomer.

What? I have only insisted that it hasn't happened, and that it's a requirement for viable fusion power.


Because a powerplant has one extra required component that a rocket doesn't- convert the reaction energy into electricity. Every known, engineered method doing that that we currently have is sufficiently inefficient that more energy is lost in conversion than the fusion reaction produces, which is why you get less usable energy out that you put in. It's easy to make energy from fusion, it's hard to get that energy in a usable form, which is what we mean by "break even". A rocket is not subject to that constraint, because the raw reaction products themselves, without conversion to any other form, are exactly what a rocket wants anyway.


I really hope this works out! But the real question is: could this be used for atmospheric thrusters on Earth?


Based on the amount of thrust it produces for the weight of the machine, not a chance.

Only works in an environment with very low friction. i.e. space


What is the thrust it generates, anyway? The article and the NASA homepage didn't state a value


http://www.nasa.gov/pdf/636883main_FDR_talk_NIAC_2012_final...., slide 15 says 0.38 kg/kW for a 30 day trip (some hand waiving included)

That sounds powerful to me. However, they also talk of pulse rates of 14s to 3m (slide 19). I guess you will have to divide that power output by some duty cycle (corrections welcome; I only browsed the PowerPoint, and wouldn't understand it, anyways)


Thanks for that link! Very good info on there about the mission parameters and the actual science behind getting to Mars using this propulsion technology. After reading Red Mars (thanks to whomever recommended that book in a previous HN post) I'm stoked that we are THIS close to getting a mission to Mars. If someone like Elon Musk (you knew someone was going to mention him) could fund this...he has the rockets to get to the space station, he could build the ship to get to Mars from there...


The article didn't mention numbers about the expected thrust of the engines, but it gave some ballpark figures to do estimates with.

The engine fires for three days to set up a mars transfer orbit. Contrast this with the trans-lunar injection with the S-IVB rocket that was used in the Apollo program, which fires for 350 seconds. Mars is a lot farther away than the moon, but this was the only figure I could find with a quick wikipedia search.


Why not? Aren't rocket-fueled thrusters much heavier due to the weight of the fuel alone?


There's a trade off between how efficient a thruster is, and how much power it produces over a fixed amount of time.

(Good reading is the specific impulse article on Wikipedia: http://en.wikipedia.org/wiki/Specific_Impulse )

At any given point, our technology allows us to create highly efficient but relatively "weak" engines (e.g. ion thrusters), or "powerful" but inefficient ones (e.g. rockets). Actually, both use Newton's second law to generate thrust, i.e. some kind of material has to exit the engine in the opposite direction, in order to get things moving. So, even ion drives and similar designs carry some material for the purpose of being ejected, it's usually just on a completely different scale to rockets. Energy also needs to come from somewhere to facilitate this, with rockets, it's the chemical energy from the fuel itself. With ion drives, it is usually some form of electricity, generated with a solar panel or nuclear power plant, etc.

So in reality, even the efficient drives also have to carry some way to power themselves. To get more thrust, they need to have more power. If you run the maths, by the time they have enough power to overcome Earth's gravity, they need to have an entire solar farm worth of panels (which are heavy), or a rather large nuclear power station on board (which is also quite heavy). So, unless we find ways to make more powerful sources of energy, or even more ridiculously efficient drives, the thrust coming from these will not be able to overcome near-Earth gravity.


Pretty much. More mass to lift = more fuel = more mass = more fuel etc., plus burning fuel isn't the most efficient way of getting kinetic energy into the thing you are lifting.

I would say it is unsuitable for atmospheric engines because of the way it runs. Earth to Mars in 30 days will need you to be travelling at almost 90 km/second. The engine has to fire for 3 days straight because the delta v you need is retardedly high, so it pulses the engine once a minute so that the passengers don't die and the ship doesn't break up due to huge g-forces.

Lifting something into orbit needs to be done fast, because most of your energy is spent counteracting gravity, not air resistance. A slow pulsing engine would not be enough to get you up.


Three days of hammering impulse is not going to be fun!


I guess you won't feel the pulsing that much...


The four engines of an Airbus A380 provide 311 kN of thrust each, so roughly 1.2 MN or 100 tons of thrust, where the aircraft itself weighs ~500 tons (MTOW-payload).

Biggest weight point is the fuel with 320 tons... I wonder how much fuel is needed for the same energy output as the A380 engines.


Alright count me in for this trip. At least if it includes a return ticket :)


If it's in the 2040s or 2050s, and I'm into my dotage and pushing 100, I'll spring for a one-way. They can fill my return slot with someone younger, or bring home an extra 150lbs of Mars rocks.




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