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Research on fusion engine is AIAA Best Paper

uah.edu

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Re: Research on fusion engine is AIAA Best Paper

#11

Post by ChuckMcM »

stephengillie wrote: post #2

> We have developed an understanding of what propulsion systems enable missions to Mars in 90 days or less, and to otherwise reduce the trip times to the outer planets and beyond by a factor of three. - Dr. Jason Cassibry, Associate professor - Mechanical and aerospace engineering Wow, this seems tremendous. The article itself is behind a paywall. (Abstract: http://arc.aiaa.org/doi/abs/10.2514/6.2014-3520 ) Before th…

Stay out of the backwash though :-) The Dyson paper is excellent. Unfortunately, for now at least, it is hard to launch a nuclear RTG without a lot of resistance, imagine how hard it is going to be to launch what is essentially a retriggerable hydrogen bomb into orbit. Does solve a lot of 'time of flight' problems, but adds a few shielding problems of its own.

Re: Research on fusion engine is AIAA Best Paper

#12

Post by ValleyOfTheMtns »

stephengillie wrote: post #2

> We have developed an understanding of what propulsion systems enable missions to Mars in 90 days or less, and to otherwise reduce the trip times to the outer planets and beyond by a factor of three. - Dr. Jason Cassibry, Associate professor - Mechanical and aerospace engineering Wow, this seems tremendous. The article itself is behind a paywall. (Abstract: http://arc.aiaa.org/doi/abs/10.2514/6.2014-3520 ) Before th…

> And the idea of reaching Mars in months instead of years is too positive to coherently express.

I don't think getting to Mars has ever taken years. The typical numbers given are 6-8 months, depending on where Earth and Mars are in relation to each others' orbits around the Sun.

More than halving the amount of time from 8 to 3 months is still impressive though.

Re: Research on fusion engine is AIAA Best Paper

#13

Post by abecedarius »

curtis wrote: post #3

There is a related paper at: https://www.nasa.gov/sites/default/files/files/Adams_2013_Ph... I found the Executive Summary and Background sections to be pretty easy to understand, at least for this layman. I haven't read the rest of the paper yet. TLDR, assuming I understand correctly: Imagine an Orion-drive spaceship powered by tiny, tiny H-bombs where the chemical explosives have been replaced by a magnetic z-pinch…

I wonder if this could be made into a 'blaster' like in science fiction stories, here on Earth.

Re: Research on fusion engine is AIAA Best Paper

#14

Post by Animats »

Non-paywall version, direct from NASA: [1]

[http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2014001...]

It's a neat idea. It's really a pulsed fission reactor, pumped by a fusion stage that's below breakeven but produces a lot of neutrons that can ignite fission. It runs on U-238, depleted uranium, which won't fission by itself but can be pumped into fissioning. This is somewhat similar to the process that occurs in H-bombs, so it's well known nuclear physics.

Depleted uranium is about as hazardous as lead. Breathing or eating it is bad for you, but the risk is heavy-metal poisoning, not radiation. It's very heavy, so in water it will sink to the ocean floor. Launching over the ocean is indicated.

This looks promising.

Re: Research on fusion engine is AIAA Best Paper

#15

Post by mng2 »

Symmetry wrote: post #8
Symmetry wrote: post #6

In one sense that's pretty cool. In another it's hard to see where they're going to get the energy to run the fusion generator from. First some background. One of the main ways that you could get to Mars or elsewhere fast is by burning more fuel than you need to to get where you're going. If you're going to do that you don't want to have a humongous ship with lots of stages so you want something with a higher exhaust…

Hmm, so they've simulated an ISP of 6,500. That's pretty close to what you'd want. Man, it's really cool to see all those years of research into fusion power create these technologies for use by something else. I wonder what the potential for U238/D-T power reactors would be? Since you've still got fission byproducts the main advantage is that you can convert a lot of the energy produced directly into electricity via…

A fusion/fission rocket engine using a pinch seems pretty blue-sky at this point, to be honest. Their paper[0] only briefly mentions the main problem with cylindrical geometries: "With a successful Phase II award the team will test at these varying power levels z-pinch processes to drive out the progression of plasma instabilities in a z-pinch process." Pinches are not very good at being stable, and they are what people tried before going to toroidal geometry (tokamaks et al). Of course, for pulsed power you don't need your pinch to be stable for very long, but at our current state of the art it's breathtakingly inefficient.

Fusion/fission hybrids have been mooted for power production, but there are several issues. First, why make your neutrons via fusion when that's essentially the most difficult way to do it? Second, once you put uranium into your reactor, you've got the same nuclear waste problem that you've got with fission, mucking up your arguably-much-cleaner fusion process. So there are significant downsides to a hybrid system.

0: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2014001...

Re: Research on fusion engine is AIAA Best Paper

#16

Post by TeMPOraL »

vilhelm_s wrote: post #10
stephengillie wrote: post #2

> We have developed an understanding of what propulsion systems enable missions to Mars in 90 days or less, and to otherwise reduce the trip times to the outer planets and beyond by a factor of three. - Dr. Jason Cassibry, Associate professor - Mechanical and aerospace engineering Wow, this seems tremendous. The article itself is behind a paywall. (Abstract: http://arc.aiaa.org/doi/abs/10.2514/6.2014-3520 ) Before th…

The book "Project Orion: The True Story of the Atomic Spaceship" by George Dyson is really fascinating. The Orion project was all done before the Apollo project was planned, so it is kindof an alternative way the US space program could have gone. Rather than launching dinky little space capsules, they were planning on launching thousands of tonnes into orbit. The spaceship would be a literal space ship , build simila…

The simple thought of having that much Δv in a craft that heavy pretty much blows my mind...

Re: Research on fusion engine is AIAA Best Paper

#17

Post by TeMPOraL »

ValleyOfTheMtns wrote: post #12
stephengillie wrote: post #2

> We have developed an understanding of what propulsion systems enable missions to Mars in 90 days or less, and to otherwise reduce the trip times to the outer planets and beyond by a factor of three. - Dr. Jason Cassibry, Associate professor - Mechanical and aerospace engineering Wow, this seems tremendous. The article itself is behind a paywall. (Abstract: http://arc.aiaa.org/doi/abs/10.2514/6.2014-3520 ) Before th…

> And the idea of reaching Mars in months instead of years is too positive to coherently express. I don't think getting to Mars has ever taken years. The typical numbers given are 6-8 months, depending on where Earth and Mars are in relation to each others' orbits around the Sun. More than halving the amount of time from 8 to 3 months is still impressive though.

> More than halving the amount of time from 8 to 3 months is still impressive though.

That also suggests lots of spare Δv that could be used for going places.

Re: Research on fusion engine is AIAA Best Paper

#18

Post by Symmetry »

ChuckMcM wrote: post #11
stephengillie wrote: post #2

> We have developed an understanding of what propulsion systems enable missions to Mars in 90 days or less, and to otherwise reduce the trip times to the outer planets and beyond by a factor of three. - Dr. Jason Cassibry, Associate professor - Mechanical and aerospace engineering Wow, this seems tremendous. The article itself is behind a paywall. (Abstract: http://arc.aiaa.org/doi/abs/10.2514/6.2014-3520 ) Before th…

Stay out of the backwash though :-) The Dyson paper is excellent. Unfortunately, for now at least, it is hard to launch a nuclear RTG without a lot of resistance, imagine how hard it is going to be to launch what is essentially a retriggerable hydrogen bomb into orbit. Does solve a lot of 'time of flight' problems, but adds a few shielding problems of its own.

Project Orion had much more thrust than this proposal but also came attached to a very heavy lifter plate and set of shock absorbers. That meant that the only feasible way to get Orion up to orbit was for it to fly there under its own power. That means that all the radioactive byproducts were going to end up in the atmosphere. Each bomb is tiny but you'll need a lot of them and it adds up.

By contrast this drive is designed to be used in space and once you're outside the Van Allen belt you're pretty much fine to use nuclear drives. The fact that there aren't any critical masses involved also means that you're not violating the Outer Space Treaty.

Re: Research on fusion engine is AIAA Best Paper

#19

Post by Symmetry »

mng2 wrote: post #15
Symmetry wrote: post #8

Earlier quoted context omitted.

Hmm, so they've simulated an ISP of 6,500. That's pretty close to what you'd want. Man, it's really cool to see all those years of research into fusion power create these technologies for use by something else. I wonder what the potential for U238/D-T power reactors would be? Since you've still got fission byproducts the main advantage is that you can convert a lot of the energy produced directly into electricity via…

A fusion/fission rocket engine using a pinch seems pretty blue-sky at this point, to be honest. Their paper[0] only briefly mentions the main problem with cylindrical geometries: "With a successful Phase II award the team will test at these varying power levels z-pinch processes to drive out the progression of plasma instabilities in a z-pinch process." Pinches are not very good at being stable, and they are what peo…

Well, for a space drive it's really attractive because combining the fuel and propellant lets you get around a lot of worries regarding things melting. The big limiting factor around conventional nuclear thermal drives is that the fuel wants to melt before it gets hot enough to give you the sort of ISPs you really want.

You can have pure fission designs where your fuel is mixed with or only in contact with your propellant like the gas core[1] or the nuclear saltwater[2] rockets but those are in constant danger of exploding.

[1]http://en.wikipedia.org/wiki/Gas_core_reactor_rocket

[2]http://en.wikipedia.org/wiki/Nuclear_salt-water_rocket

Re: Research on fusion engine is AIAA Best Paper

#20

Post by TheLoneWolfling »

TeMPOraL wrote: post #16
vilhelm_s wrote: post #10

Earlier quoted context omitted.

The book "Project Orion: The True Story of the Atomic Spaceship" by George Dyson is really fascinating. The Orion project was all done before the Apollo project was planned, so it is kindof an alternative way the US space program could have gone. Rather than launching dinky little space capsules, they were planning on launching thousands of tonnes into orbit. The spaceship would be a literal space ship , build simila…

The simple thought of having that much Δv in a craft that heavy pretty much blows my mind...

That much Δv at a decent TWR, too...
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