NASA-backed fusion engine could cut Mars trip down to 30 days
theregister.co.uk
theregister.co.uk
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.
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 ...
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.
The real problems for the Orion are political and frying of satellite electronics, iirc.
Why you make assumption that bombs must be delivered to space vs constructed there from resources mined in asteroids?
Converting uranium to uranium hexafluoride, centrifuging it over and over, then converting it back requires massive industrial facilities, currently impossible in space.
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).
Furthermore, nuclear weapons have been sent to space before, both for regular long-range missiles and for EMP-like tests.
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.)
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.
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.
And I've never heard of a Kalman line and google comes up with nothing.
(Verne's Nautilus was powered by primitive batteries.)
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.
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.
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.
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.
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 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.
I would guess that the EMP would be dangerous to satellites, but I'm sure there are ways to mitigate that as well.
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.
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."
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.
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.
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.
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.
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?
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.
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.
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.
But I wonder if the radiation exhaust might be to high to be practical on earth.
[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!]
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.
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.
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.
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].
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.
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.
Nowhere near break even though.
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.
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:
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.
And yes I was referring to the Fusor linked below. That is hot fusion.
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.
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!)
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.
Why not? The energy to start the reactor comes from solar power, so they didn't have to carry it up with them.
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).
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.
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.
Existing ion thrusters don't give enough thrust to get to Mars in 30 days.
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.
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.
Ion engines have weight, too. What leads you to believe that the fusion hardware will be heavier?
- 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.
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.
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 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).
> 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.
In this way a system can be simultaneously useful for space travel but useless for power generation.
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.
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.
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)
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.
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.
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.
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.
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.
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.
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.
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?
> 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.
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.
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.
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
> 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.
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.
To date, there have been no -- that's NO -- laboratory fusion generators that produce more power than they require for initiation.
> 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.
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.
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.
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).
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.
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.
The proposal specifically says they will not convert the energy to electricity, but will use the reaction directly for thrust.
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.
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).
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.
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...
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.
Having said that, Space X seems like it offers the best of both worlds.
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.
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!
There's a lot of people on HN who could double that budget without blinking, he hinted.
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)
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 (?)
Thus, in space all those different particles will fly off in different directions at 30km/sec. They'll be harmless in microseconds.
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).
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).
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.
http://www.alternative-energy-action-now.com/general-fusion....
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.
What? I have only insisted that it hasn't happened, and that it's a requirement for viable fusion power.
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)
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. :)
Only works in an environment with very low friction. i.e. space
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.
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)
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.
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.
(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.