Nuclear Propulsion - The best way for space travel

Preston · 2003-03-04 13:05:21

It takes a fission reactor to get all of this going, but in the steady state, you might sap some of the fusion rocket's power and convert it to electricity so that some of it's output is used to keep it going.

Josh Cryer · 2003-03-04 18:09:55

That's what your magnets do.

Yeah, but they need a lot of power, which is basically what Robert was getting at. A fusion engine can't just shoot out plasma, it has to create energy so that you can run all the necessary systems which keep it from melting the craft to bits.

And that ain't going to be so easy.

dicktice · 2003-03-05 12:53:16

Euler: As I intended, but didn't state it possibly, in so many words, was...Orbital velocity changes would be accomplished by means of solar thermal rocket propulsion--concave mirror concentrating solar radiation to generate super-heated steam reaction jets. Different orbital velocities, from zero to plus or minus, could then be combined vectorally with the magnitude of the radial "push" vector contributed by the Solar Wind particles on the plasma cloud, whose size would be "throttled" by controlling the superconducting electromagnet's field strength. Still seems simple and viable, to me.

soph · 2003-03-08 08:52:27

That's what your magnets do.
Yeah, but they need a lot of power, which is basically what Robert was getting at. A fusion engine can't just shoot out plasma, it has to create energy so that you can run all the necessary systems which keep it from melting the craft to bits.
And that ain't going to be so easy.

First of all, it doesn't shoot out plasma, it leaks out plasma. No force is required to release the plasma-it leaves because you place a "leaky" magnet at the thrust end of the drive.

Second of all, the fusion reactor generates power, that can sustain the reaction itself. ITER plans to have a reactor that has a net gain of 14x the input power in a sustained fusion reaction by 2014.

soph · 2003-03-09 20:26:55

What if we used solar panels to maintain our fusion reaction?

nebob2 · 2003-03-11 11:37:45

That would really limit where you could go with the rocket, and those solar pannels would have to be HUGE. Even if you plan on trying to run a bimodal reactor (personaly I would just keep the fusion engine an engine, it would make life simpler)you still need a lot of power to get the reaction started, and will likely mean fission reactors.

nathan_forst · 2003-03-11 12:12:26

If you stop by Nuclear Space you may see that I post there as well. WE NEED FUSION NUCLEAR POWER IN SPACE!!!

Josh Cryer · 2003-03-11 17:33:23

Yeah, using solar panels on a fusion ship would put us in the same boat as Plasma Sails, the only difference is that to power the magnetic couplings or whatever, you'd need miles of the things. Whereas you'd only need a small solar panel (one which creates only a few miliamps of electricity) to keep the Plasma Sail bubble charged.

Smaller is better, since small solar panels would be less susceptible to space derbis (and would actually be protected from a lot of stuff if contained within a Plasma Sail).

soph · 2003-03-11 17:37:01

but fusion is much faster. Thinking on it-fission powered fusion engines sound great-power for the ship, water propellant for sheidling, and fast speeds. Huge mass ratios too.

Josh Cryer · 2003-03-11 17:57:08

Yep, that's basically what Robert was talking about. You'd need a fission reactor to keep the fusion reactor contained. That is, assuming controlled fusion can even occur outside of stars.

soph · 2003-03-12 21:38:56

We know it can, it's just a matter of attaining it. You probably wouldn't need a fission reactor, but it would probably be beneficial.

If a fusion reactor is sufficiently efficient, it could power itself, the engine, and the ship (as an NTR can do).

A fusion reactor without fission gives the benefit of less radiation and waste. But waste is less of an issue, we can always eject it with the exhaust.

nebob2 · 2003-03-12 21:58:50

Fusion reactions are not easy to start. You would still need the fission reactor to get the reaction started. It would propably be safer to have a seperate power system running the magnetic field anyways.

Josh Cryer · 2003-03-12 22:08:27

Definitely, what happens if the fusion reactors power generator failed? You'd want at least one level of redundency. The magnetic field only needs to fail for a very very small ammount of time before the ship becomes bits of ionized particles.

Preston · 2003-03-13 00:37:41

Loss of magnetic field results in immediate dissipation. There is no danger. If it happens too often, though, the wall is damaged.

Josh Cryer · 2003-03-13 06:44:55

Hmm, wouldn't there still be a crapload of thermal heat left? I don't think you could get rid of it all, unless you had a backup that vented the whole thing somehow. Just because fusion reactions stop, doesn't mean the whole thing simple becomes cool. There's going to be lots of leftover energy just waiting to be absorbed, and since you wouldn't have magnets to contain that heat, it would be absorbed directly into the ship.

Is this logic sound?

Preston · 2003-03-13 10:31:24

Well, magnetic fields don't suddenly disappear, certainly, not in the timeframe of a disruption event. Actual loss of confinement is a process wherein instabilities occur and the thermal energy might be deposited in less than 300 ms. The FIRE reactor will be able to detect almost all of those disruptions ahead of time to mitigate the effects (I read something about 280 m/s water jets, actually).

This has some info:
http://www.et.anl.gov/sections/cph/rese … d_hpi.html

In light of the countless pulsed magnetic confinement reactors that have been operating for decades, loss of confinement is certainly not something that causes catastrophic damage. It happens a lot. It's mostly a problem that causes a few mm of the inner wall to be evaporated over the lifetime of the reactor, something which will happen much more infrequently when the technology is more perfected and steady-state.

Josh Cryer · 2003-03-13 11:09:13

Thanks for the link, that helps me understand a lot more. What kind of magnetic fields are we talking about here, though? As of now magnetic fields are powered by an outside source, right? soph was talking about magnetic fields powered by the fusion reactor itself. I'm getting conflicting positions from you. One, that loss of a magnetic field results in dissipation (I assume that means the fusion reaction stops- not that the thermal energy magically disappears). And two, that the magnetic field wouldn't suddenly disappear for some reason (outside source?).

And aren't fusion reactors destined to get hotter and hotter?

Preston · 2003-03-13 11:46:03

My understanding of it wasn't very clear at first -- you said that loss of magnetic field will cause loss of confinement, and that's true, but it turns out that instabilities are a much more common causes of loss of confinement.

I said: "Well, magnetic fields don't suddenly disappear, certainly, not in the timeframe of a disruption event."
This may not have been the best way to say it, but I meant to say that loss of a magnetic field is a different kind of problem -- that happens in a longer amount of time -- and inherent instabilities in the plasma itself are what cause loss of confinement.

When soph says the fusion reaction powers the magnetic field, he means that the ship generates electricity from the fusion reaction, and then that electricity is used to power magnets. This might occur with a stable rocket, but to get things going, you need a fission reactor - an outside source - to run the cooling and start current in the superconducting magnetics, as well as heat the plasma (initially) and run other systems.

The first DT reactors will run around 15-25 keV (first commercial reactors will handle ~10 MW/m^2 flux) , and D3He reactors will run around 50keV. At the same time, plasma facing compontents (PFC) technology will advance too. For example, in areas where disruptions occur there will be liquid metal PFCs (these are applied only to problem areas) that can handle ~50 MW/m^2, and there is an intermediate material related to tungsten that handles ~25 MW/m^2.

soph · 2003-03-13 17:22:43

I was thinking me might be able to "spark" the reaction from an offboard source ("plug it in" to an orbital reactor), and keep the ship fission-free.

Preston · 2003-03-13 20:38:11

That's an interesting idea, but you'd have to leave the engine on -- and hope against hope you don't run into any problems. I wouldn't want to get caught with an excess of 30 km/s inbound to Jupiter and fly straight out of the system.

soph · 2003-03-13 20:43:09

Well, by the time that these big interplanetary lugs are in operation, I would think we would have deep system outposts (ex, asteroid belt) that could send rescue ships to slow down/jumpstart our derelict ship.

but you would have the same issue with any single engine system, solar/plasma/NTR, etc. A good way to backup is to have a small fusion reactor as a backup (maybe even running on a minimal mode to allow it to be turned up and used at a moment's notice), and redundant fusion engines. My assumption is that you would have more than one engine anyway, to produce more thrust. Even if you don't use all your engines, you have redundancy. The thermal heat from the first reactor, that Josh mentioned, could be used to start another reactor, along with energy from emergency fuel cells.

tim_perdue · 2003-03-14 12:21:09

For example, nuclear energy ?doesn't? release CO2, but the production of HEU does.

Why? This old canard is absurd. First, only about 2% of a nuclear plant's output is required to refine the uranium, and second why not just use nuclear power to power the HEU generators?

You sound thoroughly propagandized by the anti-nuclear crowd.

It would be quite trivial to show cases where nuclear energy is just as evil as coal or other forms. The only truely benign energy source is solar. Anyone pretending otherwise is in major denial.

Unlikely, even if we entered this fantasy world where we burn wood and cornstalks to run all our generators. It takes a ton of DIESEL fuel to harvest and shred all this material to transport it to the power plant. What about watering and perhaps planting all the plant material?

Your own argument about "environmental damage" caused by mining/refining uranium has shown you are irrational, since your "solar obsession" causes far, far more damage.

Josh Cryer · 2003-03-15 06:45:58

First, only about 2% of a nuclear plant's output is required to refine the uranium, and second why not just use nuclear power to power the HEU generators?

Certainly. Any system which is totally self contained isn't going to pollute. If you've read my comments about these things you'd know. Currently though, it is a fact that the HEU mining and refining process does create CO2. How do you think the mining equipment is powered? Fossil fuel or nuclear derived energies?

It's a small ammount, of course, which I did think I said (I'm not about to scroll back up, since that was way back in the thread and it did manage to get itself back on a space based topic); it just shows that, sure, all industries are going to spin the facts. Nuclear proponents say that nuclear doesn't create CO2. This is simply a lie.

And solar advocates say that their energies are clean, and don't produce greenhouse gasses and so on, yet in some cases they outsource fossil fuel energies to keep their systems optimal. This is a lie, too.

You sound thoroughly propagandized by the anti-nuclear crowd.

Why thank you, and you sound like you're not exactly thinking through what I was saying.

It takes a ton of DIESEL fuel to harvest and shred all this material to transport it to the power plant.

Um, why can't it be biodiesel? I don't think you're seeing the whole picture here. Pyrolysis can be done in many varieties of ways, but shredding isn't really necessary. Pyrolysis is self contained, that is, the gases and charcoal created by it are enough to keep the recycler going, naturally. No outside sources of energy are necessary (unlike with some forms of ?ecofriendly? technology- as someone pointed out). Biodiesel is trival to refine from the byproducts of the pyrolysis process (unlike refining gasoline from fossil sources).

What about watering and perhaps planting all the plant material?

Well, first, I advocate biomass technological advancements. ?Naturality? is unnecessary. Genetically engineered plant machine hybrids are perfectly fine with me. We could paint our houses with the stuff. It'd be 50%+ efficient, depending on what color you chose.

The point is just to show that even now, with technology 2000 years old (pyrolysis is a very old process), we can wean ourselves off of forms of centralized energy.

Your own argument about "environmental damage" caused by mining/refining uranium has shown you are irrational, since your "solar obsession" causes far, far more damage.

And yet, you didn't even show how. You just made a statement and somehow magically it's going to be true. My ?solar obsession? has to do with one very small fact. Nothing in this orbit can produce the kind of energy we get from the sun. Nothing. What, may I ask, is wrong with pointing this out?

I wonder what nuclear space proponents are going to do when M2P2 takes off.

soph · 2003-03-15 09:10:15

They're going to show that nuclear has its own benefits that in many cases outweigh M2P2, just as I did.

Why not fuel cells? Fuel cells could be on every house, generate more jobs to produce, and generate water for every house.

And yet, you didn't even show how. You just made a statement and somehow magically it's going to be true. My ?solar obsession? has to do with one very small fact. Nothing in this orbit can produce the kind of energy we get from the sun. Nothing. What, may I ask, is wrong with pointing this out?

But many processes can harness the energy they produce more efficiently.

As I pointed out before, there wouldn't be the mass mining you seem to imagine. You wouldn't be mining 100,000 kg of uranium if you only needed 100 kg. It simply doesn't make sense. Especially since the government could regulate the mining of uranium.

Josh Cryer · 2003-03-16 08:35:02

Let's not get this back off topic, please, soph? I shouldn't have responded to Tim... I feel bad that like 4 pages of this whole thread weren't deveoted to interplanetary transportation (my fault, too).

Here's something I was wondering about. Wouldn't solar radiation affect the fusion chambers stablity? The magnetic field might fluctuate depending on how bad the weather is outside the ship. So it would have to be shielded somehow, I would think. Who wants a ship that goes really fast, but becomes unstable and has to be temporarily shut down the first momment a storm hits?

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