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Fusion Rocket Could Take Us To Mars
New submitter imikem writes "University of Washington researchers and scientists at a Redmond-based space-propulsion company are building components of a fusion-powered rocket aimed to clear many of the hurdles that block deep space travel, including long times in transit, exorbitant costs and health risks. 'Using existing rocket fuels, it's nearly impossible for humans to explore much beyond Earth,' said lead researcher John Slough, a UW research associate professor of aeronautics and astronautics. 'We are hoping to give us a much more powerful source of energy in space that could eventually lead to making interplanetary travel commonplace.' 'The research team has developed a type of plasma that is encased in its own magnetic field. Nuclear fusion occurs when this plasma is compressed to high pressure with a magnetic field. The team has successfully tested this technique in the lab. Only a small amount of fusion is needed to power a rocket – a small grain of sand of this material has the same energy content as 1 gallon of rocket fuel.'"
And if the fuels take more energy to prepare than they yield when reacted(tritium is one such fuel), then they're not very useful for energy production, but very useful for energy storage.
How is the electricity produced in the space ship for the nuclear fusion, would it also be nuclear? "The capacitors are hooked up to a giant magnet that houses the chamber where the fusion reaction will take place. With the flip of a switch, the capacitors are simultaneously triggered to deliver 1 million amps of electricity for a fraction of a second to the magnet, which quickly compresses the metal ring."
Some people die at 25 and aren't buried until 75. -Benjamin Franklin
I don't think practical fusion technologies are as far away as you're acting like they are. If you've been following fusion news, there are several projects that are getting pretty close to scientific net+(my favorite is the Focus Fusion experiment).
There are a few small details to deal with regarding both potential technologies.
Except we know how to create uncontrolled fusion, and a fusion rocket is closer to a hydrogen bomb than a fusion reactor. You're just trying to make fusion happen and throw the resulting plasma out the back, not keep the plasma in one place and generate power from it.
The purpose of this engine is to generate a very high speed ionized spray of lithium in a specific direction. How would that be converted into electrical energy? Generating kinetic energy (especially in space where waste byproducts just kinda go away) is extremely easy compared to generating electrical power.
Better known as 318230.
We've had nuclear fusion working for over sixty years now. The trick has been containing it in a reactor for power generation. A fusion rocket might be easier to pull off--that's essentially just a semi-contained and directed H-bomb.
This. It's all about specific impulse in space travel - which is a very separate concept to net energy production. There's no problem spending a lot of energy making rocket fuels on Earth, when the big cost multiplier is launch mass.
Creating a fusion reaction to create a very-hot-indeed metal plasma and spit the lot into outer space is one thing.
Creating a fusion reaction and containing the very-hot-indeed reaction inside a box, so you can draw off the heat to run a turbine, as multiple generations of despondent physicists will tell you, that's something else.
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Prisencolinensinainciusol. Ol Rait!
Worth noting, is that this concept is essentially the Orion engine without the heavy radioactives - the idea is essentially what we do in the hydrogen bomb.
High-speed ions would actually be easier and more efficient to use for generating electricity than conventional thermal energy. You set up an opposing electric field with a voltage that corresponds to the ions' energy in MeV, and capture them once they've slowed down. This creates a direct electric current at that high voltage, without the need for Carnot cycles, steam equipment, heat exchangers, etc.
One of the attractions of aneutronic fusion is that most of the energy is released in the form of charged ions that can be harnessed in this way.
The Trisops machine at the University of Miami.
Disclosure: I am one of the authors of the cited paper in the article and the author of the above Wikipedia article
What about radiation shielding?
Lets not forget that the objective of the rocket is to move you, not generate usable energy. You don't necessarily have to have a net+ for this to be useful.
Think of it as a super high density fuel that just takes a lot of energy on the ground to process.
For large sets, this will be our guide even unto death, for the LORD will work for each type of data it is applied to...
boom.
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OK, think about those ridiculously high watt lasers. Recall how those are pulsed?
So is this, with a period of a minute or so. (large amount of energy in a tiny period of time, with a long 'idle' phase between). A traditional fission reactor or RTG could be used to charge the capacitor system for this, as well as the other ship systems.
For large sets, this will be our guide even unto death, for the LORD will work for each type of data it is applied to...
âoeUsing existing rocket fuels, itâ(TM)s nearly impossible for humans to explore much beyond Earth,â said lead researcher John Slough, a UW research associate professor of aeronautics and astronautics. âoeWe are hoping to give us a much more powerful source of energy in space that could eventually lead to making interplanetary travel commonplace.â
[...]
NASA estimates a round-trip human expedition to Mars would take more than four years using current technology. The sheer amount of chemical rocket fuel needed in space would be extremely expensive â" the launch costs alone would be more than $12 billion.
That's not true at all. Chemical rockets work as well. And with the Falcon Heavy in the near future, there's no reason to pay $12 billion in launch costs for a Mars mission, even if you use chemical rockets.
Note also the phrase "take more than four years". That makes it sound like it takes two years to come and go from Mars. It really only takes six months with chemical rockets (plus some time for attaining Mars orbit, there's probably not going to be a direct landing on Mars due to the high risks of aerocapture) The reason it would take that long is because humans would be staying on the surface of Mars for at least two years. I doubt even instantaneous travel would cut off more than a year and a half.
The more reasonable 90 day passage to Mars would takes six months off the travel time plus reduce the time needed to get into Mars orbit. It would also enable trips at any time rather than just during the most optimal trajectories. This really is the key constraint of chemical rockets.
At this point, it is worth noting that there are other viable near future propulsion technologies as well. A key one is electric propulsion which can be solar or nuclear powered. It has a good mass fraction and travel times. Solar sails could be used to ferry radiation-immune loads over very slowly.
In space no one can hear you boom.
That's no problem. They use platics for that.
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Is English not your first language? (honest question, sometimes nuances can be lost) "As small as a grain of sand" is just a phrase, used to denote something tiny. Sounds like a word or such just got left out of the phrase - I can assure you they're not trying to use actual sand for fusion. Redmond may have nutjobs living there, but doing that would be beyond even them.
It was the NERVA rocket. it wasn't fusion, but it was a nuclear-powered rocket, and it would have easily made Mars our bitch.
It was canceled to, fucking get this, no seriously, wait for it. It was canceled TO SAVE THE BUDGET because the politicos at the time were afraid a successful Mars rocket would "drag" the US into this huge "space program" where we'd explore the solar system and stuff. And that would cost a lot of money.
Instead, we killed the NERVA rocket and saved our budget for Vietnam, which was a roaring success that paid incredible dividends . . . . oh, fuck.
Anyway, this is nice to hear, but I'm not going to hold my fucking breath. Our national priorities are far too ass-backwards for something forward-looking like a Mars mission. I suspect the first people to land on Mars will likely be an international team, and America will be riding along in the back begging for a look out the front window from time to time.
One day I feel I'm ahead of the wheel / the next it's rolling over me / I can get back on / I can get back on
You need plenty of neutron shielding for fusion. But the advantage of having a spacecraft over a power plant is that you can use distance, by putting it on the end of a long structure, and that you won't care what the neutrons will do to the shielding and equipment on timescales longer than the mission.
I hear we're about 40 years away from viable fusion technology.
Actually, they're not. What they're creating is more akin to uncontrolled thermonuclear fusion.
Pretty much mini-bombs without the fission primary. Still pretty much bombs though. Usable for a rocket, not usable for electrical generation.
Also, even if it doesn't achieve breakeven, it may still be able to achieve very good Isp - e.g. lots of thrust per gram of propellant mass.
retrorocket.o not found, launch anyway?
So suppose this works as described and we have a functional method of initiating pulses of controlled fusion in a rocket engine that when vented out the nozzle produces usable thrust. Let's make that nozzle thinner and a bit more tubular than conical - a few hefty magnets around to to keep all that fusing stuff in a nice thin stream. While we're at it lets anchor the other end of the rocket to something HUGE that the thrust isn't going to have a prayer of shifting. Except here we call it recoil, because if you have made a fusion rocket you have also created the other staple of grand space opera... A plasma cannon :)
I had a
Ok, apologies if this is a joke that's wooshing over my head, but nuclear fusion produces very little radiation. A small fraction of the reaction energy is released in neutrons and some x-rays. Most of the energy is released as heat. I'm not a nuclear physicist, but hydrogen fusion is causing hydrogen atoms to smack into each other with enough energy that they fuse producing helium and a very large amount of energy. You're thinking perhaps of fission, which is when radioactive isotopes give off energy as they change into different radioactive isotopes. It's a completely different thing.
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My understanding is that there was a re-examination in the 1970s by General Atomic into the original Orion project, but using a fusion power source rather than fission. The Pentagram immediately classified the report though, probably because they didn't want "the enemy" to know about the actual output of the small fusion devices, and it's never seen the light of day.
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The devices we call 'hydrogen bombs' are not pure fusion explosives. They are more correctly known as 'hydrogen-boosted fission' devices. The hydrogen fusion is used to provide more neutrons to sustain the fission reaction, but in most cases the majority of the energy still comes from fission.
(At least, that's my understanding.)
Correct. Fission --> Fusion --> Lots More Fission --> Very Big Kaboom
Although the energy density of hydrogen fusion is greater than that of Uranium/Plutonium fission, the energy of individual fusion reactions are generally much less energetic than individual fission ones. H-bombs are crazy because fusion produces high-energy neutrons (and lots of 'em), which are sufficient to cause fission in normally non-fissile U238. So, they jacket the fusion part with cheap U238, which is useful as a tamper for slow neutrons until the fusion fuel ignites (by way of energy from a separate, fission primary), after which the cheap U238 is fuel for boosting the yield off the charts.
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Question, does your car require you to carry around raw, unprocessed oil, complete with an oil refinery to convert it into gasoline, or can you just fill it straight with gasoline?
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All of the fusion projects that I'm aware of are not only heavy, they're also delicate, and require lots of skilled technical attention.
I'd say we're *at least* two decades from a fusion engine that's practical in a spaceship. Three or four wouldn't surprise me. And I also wouldn't be totally surprised if it is one of those things that can just never be made practical (though I'd be very disappoiinted).
For that matter, while several of the fusion projects appear to be near the technical "break even" point, I can't think of one of them that's even approaching the economic break even point. Even fission is a bit dubious about that, when you count in all if the expenses. (E.g., government providing "insurance" against massive problems [in the form of saying "you won't be held liable"], and what to do with spent reactors and fuel.) That said, one mussn't forget that coal also gets massive subsidies, if only in the form of permission to engage in environmental degradation and pollution.
Note that all mining is environmentally destructive, and it is rare for the costs of that destructuion to be included in the cost of the products of the mining. So it's quite difficult to come to a rational balance of which technology is more expensive. Fusion has the problem that it's less dependant on mining, so it doesn't get the benefit of free pollution of the environment. This makes it more difficult for it to compete with established technologies. But it's not even nearly ready yet anyway. None of the existing projects have passed the technological break even point, which is a lot easier than the economic break even point.
I think we've pushed this "anyone can grow up to be president" thing too far.
All of the fusion projects that I'm aware of are not only heavy, they're also delicate, and require lots of skilled technical attention.
All of the ones I've worked on were quite robust and solid for the basic structure, as they basic plasma is created and managed with not much more than just a large vacuum vessel, magnets and some power supplies or capacitor banks. This is to the point no one would bother with ladders half the time, because the large bolts and plates on the vacuum vessel turned it into essentially a giant jungle gym that let you get to wherever you needed to on the machine. What tended to be really fragile on the other hand were a lot of the diagnostics, especially stuff like precision optics for spectroscopy or laser based diagnostics, imaging diagnostics, x-ray diagnostics, probes that were stuck into the plasma and shielded with ceramics. But an operating machine would not need 90+% of the diagnostics, and can probably get by on things like magnetic diagnostics that can be made rock solid. I think you could probably go at some of the machines with a sledgehammer, and as long as you avoided the windows on the vacuum vessel and the diagnostics, it would take you a while to do any actual damage.
About the only exception might be some of the heating techniques being used, although those are mostly only relevant to getting steady state reactors going. And those consist of things like high power RF, which the military has some experience with making resilient, and things like neutral beams which would be on par with ion engines that we've already tested in space.
And from your other comment:
Even if ground based fusion reactors turn out to be cheap and simple in the near term, I have severe doubts about thier suitablitity for powering a spaceship until a LOT more development is done.
Assuming there is a demand and hence money for development, I would expect fusion engines to be developed long before ground based fusion reactors are made practical. There are much fewer constraints or much looser constraints for using fusion as propulsion than as a primary source of energy. If you view it as a process for converting electricity into propulsion, you can get by with a lot less efficiency than something that is trying to produce electricity through inefficiency conversion and additionally kept itself going. Because you don't have to worry about contaminating your environment, you have a lot more flexibility and choice in construction materials, and don't need designs that are meant to last decades. The only additional constrain would be worry about mass, but then you at least don't need a whole vacuum vessel and all of the vacuum equipment.
Here is a video of a scientist named Charles Chase who works for Lockheed Martin Skunkworks. The presentation is made at Google's "Solve for X". The video is 14 minutes long so I'll give an executive summary. Chase claims that his team has made a breakthrough in developing a small fusion reactor that will lead to a 100MW reactor the size of a truck trailer and of the complexity of a jet engine. The prototype they have built is a cylinder 1m in diameter by 2m long. In their experiment they put deuterium gas into a magnetically confined space and heat it up with radiofrequency energy. He infers that the confined plasma is reaching the conditions necessary for fusion to occur. The reactor is "high beta", with "beta" referring to the ratio of the magnetic field pressure to the pressure of the plasma pushing out. He says that the magnetic field strength in the reactor increases as you go out from the centre of the plasma, thus creating an extremely effective plasma confinement. He contrasts this with a Tokamak reactor, where the magnetic field is generated by the moving plasma itself, and thus decreases in strength out from the centre of the plasma. He says that this decreasing field strength is the main problem with Tokamak reactors and that it causes the confinement to be unstable. If the confinement becomes unstable, the magnetic field decreases, thus creating a negative feedback loop. This contrasts with his reactor design, that tends to create a far more stable plasma confinement.
I have a background in physics and what this man says in his video makes sense to me. It is of course short on details, but what would you expect for a short presentation. And you wouldn't expect a Skunkworks scientist to publish information in the same way as a university scientist. I have often puzzled in the past as to why we can't use an elegant method of magnetic confinement to achieve the conditions for fusion on a small scale. Tokamak seems an inelegant dead end. I think that if you can adequately confine the plasma, you have solved the energy balance problem that has plagued fusion reactors in the past.
Watch the video and see what you think.
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Think of it as a super high density fuel that just takes a lot of energy on the ground to process.
It doesn't even have to be exothermic (net energy gain) on the spacecraft, without considering any ground processing. In other words, it's perfectly fine if, for each kWh of electric energy you supply into the engine, you only get e.g. 0.4 kWh of kinetic energy of exhaust gases (plasma) coming out of the engine's nozzle. What's much more important is that the engine puts that 0.4 kWh into a very tiny amount of plasma, so that the plasma's velocity is very high (for a given amount of kinetic energy, the velocity is proportional to the reciprocal of the square root of the mass). That velocity is the "specific impulse" of the engine, and it determines how much fuel mass you need to achieve a given delta-v of the vehicle.