Reply to topic  [ 485 posts ]  Go to page Previous  1 ... 16, 17, 18, 19, 20
The "Real Aerospace" Thread 
Author Message
User avatar

Joined: Sat Mar 05, 2011 6:24 am
Posts: 398
Post Re: The "Real Aerospace" Thread
Mr.Tucker wrote:
Ok, ok, so I've just had an exciting idea for space travel, and I thought that this would be a good place to share it. Some opinions (maybe there are some nuclear engineers or such browsing this page) are welcome.
Some background: first, I was watching the presentation the liquid fluoride thorium reactor (good idea to watch it, so you know where I'm coming from):
https://www.youtube.com/watch?v=YVSmf_qmkbg
And was intrigued when mister Sorensen presented the products that such a reactor would produce. He mentioned medical molybdenum, that fascinating bismuth-213 isotope used for targeted alpha therapy, plutonium-242 for deep space RTG missions, all the good stuff.... and xenon. Which is something of an annoying byproduct (acts as a neutron poison). And it produces quite a lot of the stuff, apparently (which tends to be a problem in solid-fuel rod pressurised reactors):
https://i.imgur.com/xjfA8.jpg
So I thought: hmph, loads of power (as one tends to get with nuclear) and xenon byproduct...what needs loads of power and uses xenon?....
This does:
https://en.wikipedia.org/wiki/Dual-Stage_4-Grid
A ship that uses a LFTR reactor to power a beefed up ion thruster with specific impulse in the tens of thousands of seconds, AND doesn't need to carry much propellant (perhaps an initial charge before the reactor spools up) because it gets produced in the reactor itself. Separate it from the salt (which is easy; one is a gas, one is a liquid), and feed it to the ion drive. An NEP with a mesmerising potential.
Some would say: "ah, but reactors tend to be heavy". Firstly, it's space, so that is less of a problem. But, and more importantly, MSR's were designed during the 50's and 60's to power NUCLEAR BOMBERS:
https://en.wikipedia.org/wiki/Aircraft_ ... Propulsion
If you give an aero engineer a list of potential types of reactors he can use to power his jet engines, he will invariably choose the one that is most compact and light (I should know, I'm an aero engineer...). So, although I have no proof whether that was actually the case, I suspect that this type of reactor is extremely light and compact compared to it's opponents.
So...am I talking nonsense?


For nuclear-electric systems, it's not just the reactor, but also shielding, all the power conversion machinery to turn thermal power into electrical power, radiators, etc. And the mass does still matter in space.

As for the xenon, just consider the relative mass of the reactor fuel and a typical xenon propellant tank. A reasonable craft might carry a few tens of kg of fissile fuel and burn only grams of that during any given trip, while carrying multiple tons of propellant...even the Dawn probe carried 425 kg of xenon. You're just not going to get enough xenon to be worth the equipment needed to collect it.

There are conceptual designs for fission fragment rockets that actually directly use the fission products as reaction mass. These have specific impulses in the range of 100k to 1M seconds, but due to the geometric issues of allowing the fission fragments to escape the fuel, they wouldn't be liquid salt reactors...the fuel would be something like fine wires, thin disks/ribbons, or suspended particles of dust.


Sun Sep 02, 2018 10:30 am
Profile
Site Admin
User avatar

Joined: Fri Mar 04, 2011 9:19 pm
Posts: 2628
Location: San Jose, CA
Post Re: The "Real Aerospace" Thread
Mjolnir wrote:
For nuclear-electric systems, it's not just the reactor, but also shielding, all the power conversion machinery to turn thermal power into electrical power, radiators, etc. And the mass does still matter in space.

The shielding in particular poses a significant weight problem, which was essentially what killed the Cold War nuclear-powered bomber programs (though the Soviets were able to get their prototype to fly by deliberately using inadequate shielding).

_________________
Outsider


Sun Sep 02, 2018 11:36 am
Profile WWW
User avatar

Joined: Tue Oct 29, 2013 9:45 am
Posts: 215
Post Re: The "Real Aerospace" Thread
Mjolnir wrote:
Mr.Tucker wrote:
Ok, ok, so I've just had an exciting idea for space travel, and I thought that this would be a good place to share it. Some opinions (maybe there are some nuclear engineers or such browsing this page) are welcome.
Some background: first, I was watching the presentation the liquid fluoride thorium reactor (good idea to watch it, so you know where I'm coming from):
https://www.youtube.com/watch?v=YVSmf_qmkbg
And was intrigued when mister Sorensen presented the products that such a reactor would produce. He mentioned medical molybdenum, that fascinating bismuth-213 isotope used for targeted alpha therapy, plutonium-242 for deep space RTG missions, all the good stuff.... and xenon. Which is something of an annoying byproduct (acts as a neutron poison). And it produces quite a lot of the stuff, apparently (which tends to be a problem in solid-fuel rod pressurised reactors):
https://i.imgur.com/xjfA8.jpg
So I thought: hmph, loads of power (as one tends to get with nuclear) and xenon byproduct...what needs loads of power and uses xenon?....
This does:
https://en.wikipedia.org/wiki/Dual-Stage_4-Grid
A ship that uses a LFTR reactor to power a beefed up ion thruster with specific impulse in the tens of thousands of seconds, AND doesn't need to carry much propellant (perhaps an initial charge before the reactor spools up) because it gets produced in the reactor itself. Separate it from the salt (which is easy; one is a gas, one is a liquid), and feed it to the ion drive. An NEP with a mesmerising potential.
Some would say: "ah, but reactors tend to be heavy". Firstly, it's space, so that is less of a problem. But, and more importantly, MSR's were designed during the 50's and 60's to power NUCLEAR BOMBERS:
https://en.wikipedia.org/wiki/Aircraft_ ... Propulsion
If you give an aero engineer a list of potential types of reactors he can use to power his jet engines, he will invariably choose the one that is most compact and light (I should know, I'm an aero engineer...). So, although I have no proof whether that was actually the case, I suspect that this type of reactor is extremely light and compact compared to it's opponents.
So...am I talking nonsense?


For nuclear-electric systems, it's not just the reactor, but also shielding, all the power conversion machinery to turn thermal power into electrical power, radiators, etc. And the mass does still matter in space.

As for the xenon, just consider the relative mass of the reactor fuel and a typical xenon propellant tank. A reasonable craft might carry a few tens of kg of fissile fuel and burn only grams of that during any given trip, while carrying multiple tons of propellant...even the Dawn probe carried 425 kg of xenon. You're just not going to get enough xenon to be worth the equipment needed to collect it.

There are conceptual designs for fission fragment rockets that actually directly use the fission products as reaction mass. These have specific impulses in the range of 100k to 1M seconds, but due to the geometric issues of allowing the fission fragments to escape the fuel, they wouldn't be liquid salt reactors...the fuel would be something like fine wires, thin disks/ribbons, or suspended particles of dust.


Looking at the picture:
https://imgur.com/xjfA8
It seems to me that 1000 kg of thorium would produce 125 kg of xenon. That's not a small amount, it's roughly an eight' of it's mass.
Trying to see viability would mean seeing what the necessary Isp of said engine would have to be. That means seeing how much energy each kg of propellant would have (as kinetic energy in a electric thruster). So, turning 9000 Gw*hrs to joules, we get 324*10 to the power of eleven joules in total. This is the total energy given off by 1000 kg of thorium (actually it's daughter U-233, but I digress). This is applied to 125 kg of propellant via Newton's Law, where energy is mass times velocity squared divided by two. Working backwards to find velocity, we obtain a speed of 720000 meters/sec. Thus an Isp of 72000. This is about three and a half times the Isp of the Ds4g thruster I mentioned earlier, but is doable, especially since we know the operating principle of the ds4g can be scaled up (dual-stage 4 grid means 2 stage; just add more stages for higher velocity). I'm ignoring the efficiency of the drive (which is about 85 percent; thus the Isp needn't be as high). Comparing to Dawn is misleading, because Dawn had an Isp of only 3100 (thus a jet speed of only 31000 m/sec).
A spaceship can simply separate the reactor from the payload and use a shadow shield. This is less useful on Earth because of backscattering in an atmosphere, and because the aircraft has a physical limit to size and weight. This would not apply here.


Sun Sep 02, 2018 2:34 pm
Profile
User avatar

Joined: Sat Mar 05, 2011 6:24 am
Posts: 398
Post Re: The "Real Aerospace" Thread
Mr.Tucker wrote:
Mjolnir wrote:
Mr.Tucker wrote:
Ok, ok, so I've just had an exciting idea for space travel, and I thought that this would be a good place to share it. Some opinions (maybe there are some nuclear engineers or such browsing this page) are welcome.
Some background: first, I was watching the presentation the liquid fluoride thorium reactor (good idea to watch it, so you know where I'm coming from):
https://www.youtube.com/watch?v=YVSmf_qmkbg
And was intrigued when mister Sorensen presented the products that such a reactor would produce. He mentioned medical molybdenum, that fascinating bismuth-213 isotope used for targeted alpha therapy, plutonium-242 for deep space RTG missions, all the good stuff.... and xenon. Which is something of an annoying byproduct (acts as a neutron poison). And it produces quite a lot of the stuff, apparently (which tends to be a problem in solid-fuel rod pressurised reactors):
https://i.imgur.com/xjfA8.jpg
So I thought: hmph, loads of power (as one tends to get with nuclear) and xenon byproduct...what needs loads of power and uses xenon?....
This does:
https://en.wikipedia.org/wiki/Dual-Stage_4-Grid
A ship that uses a LFTR reactor to power a beefed up ion thruster with specific impulse in the tens of thousands of seconds, AND doesn't need to carry much propellant (perhaps an initial charge before the reactor spools up) because it gets produced in the reactor itself. Separate it from the salt (which is easy; one is a gas, one is a liquid), and feed it to the ion drive. An NEP with a mesmerising potential.
Some would say: "ah, but reactors tend to be heavy". Firstly, it's space, so that is less of a problem. But, and more importantly, MSR's were designed during the 50's and 60's to power NUCLEAR BOMBERS:
https://en.wikipedia.org/wiki/Aircraft_ ... Propulsion
If you give an aero engineer a list of potential types of reactors he can use to power his jet engines, he will invariably choose the one that is most compact and light (I should know, I'm an aero engineer...). So, although I have no proof whether that was actually the case, I suspect that this type of reactor is extremely light and compact compared to it's opponents.
So...am I talking nonsense?


For nuclear-electric systems, it's not just the reactor, but also shielding, all the power conversion machinery to turn thermal power into electrical power, radiators, etc. And the mass does still matter in space.

As for the xenon, just consider the relative mass of the reactor fuel and a typical xenon propellant tank. A reasonable craft might carry a few tens of kg of fissile fuel and burn only grams of that during any given trip, while carrying multiple tons of propellant...even the Dawn probe carried 425 kg of xenon. You're just not going to get enough xenon to be worth the equipment needed to collect it.

There are conceptual designs for fission fragment rockets that actually directly use the fission products as reaction mass. These have specific impulses in the range of 100k to 1M seconds, but due to the geometric issues of allowing the fission fragments to escape the fuel, they wouldn't be liquid salt reactors...the fuel would be something like fine wires, thin disks/ribbons, or suspended particles of dust.


Looking at the picture:
https://imgur.com/xjfA8
It seems to me that 1000 kg of thorium would produce 125 kg of xenon. That's not a small amount, it's roughly an eight' of it's mass.
Trying to see viability would mean seeing what the necessary Isp of said engine would have to be. That means seeing how much energy each kg of propellant would have (as kinetic energy in a electric thruster). So, turning 9000 Gw*hrs to joules, we get 324*10 to the power of eleven joules in total. This is the total energy given off by 1000 kg of thorium (actually it's daughter U-233, but I digress). This is applied to 125 kg of propellant via Newton's Law, where energy is mass times velocity squared divided by two. Working backwards to find velocity, we obtain a speed of 720000 meters/sec. Thus an Isp of 72000. This is about three and a half times the Isp of the Ds4g thruster I mentioned earlier, but is doable, especially since we know the operating principle of the ds4g can be scaled up (dual-stage 4 grid means 2 stage; just add more stages for higher velocity). I'm ignoring the efficiency of the drive (which is about 85 percent; thus the Isp needn't be as high). Comparing to Dawn is misleading, because Dawn had an Isp of only 3100 (thus a jet speed of only 31000 m/sec).
A spaceship can simply separate the reactor from the payload and use a shadow shield. This is less useful on Earth because of backscattering in an atmosphere, and because the aircraft has a physical limit to size and weight. This would not apply here.


9000 GWh = 3.24e16 J, and that diagram shows 150 kg of Xe. Aside from that:

The "two stages" in the DS4G are ionization and acceleration. Existing thrusters ionize (or rather, extract the ions from the grid where they ionize) and accelerate in one step, which is simpler but limits the electrical potential between the grids. They add a fourth grid to handle the acceleration. You can't just add more stages or ramp up the voltage indefinitely to get higher velocities without tradeoffs. They estimate an achievable specific impulse of 19300 s (190 km/s) for their system.

Dawn had a lower specific impulse, but it also had a dry mass of only 750 kg. And space fission reactors will be relatively inefficient, due to the difficulty in radiating waste heat. If you have an incredibly high specific impulse drive, it'll work. At 10% system energy efficiency, you'd get 6.5 Mm/s exhaust velocity, 35 times the exhaust velocity and 1200 times the specific exhaust power. We don't have such a drive and aren't close to having one. Anything less than that, you're burning thorium and dumping unused power so you can use thorium as a xenon source that outmasses the xenon it provides by a factor of 7 (somewhat wasteful), or carrying tanks of xenon that trivialize what you're getting from the thorium.

With anything we might build with near-current technology, you might extract xenon for propellant from stationary power plants, but spacecraft reactors aren't going to burn enough thorium to make it a useful addition to their own reaction mass. And for some far-future system, why would you limit yourself to using the xenon? What about the other 85% of the fission products? Using 15% of your fissile fuel as propellant seems unlikely to be optimal.


Sun Sep 02, 2018 4:28 pm
Profile
User avatar

Joined: Tue Oct 29, 2013 9:45 am
Posts: 215
Post Re: The "Real Aerospace" Thread
Ah, Mjolnir, I see you too are amn of engines :D

Admittedly I was trying to calculate powers of ten at 01.00 AM, so I messed up. The isp is waaaay too high. Muh bad...

In my mind there is a hierarchy of engines: you start with chemical, proceed to solid core NTR (such as NERVA; the only reason we ain't using them right now in space is because of politics),then pulsed NTR (which has an Isp of about 17.000 sec) and the next logical step is nuclear electric. Standard NEP is having a reactor drive an engine and a propellant tank that is separate. The concept I was going for was to have the reactor do double duty, and act as both power source and reaction mass. Though separating the xenon from the salt would still require mass, which may offset any gains I get from saving on reaction mass.

Ah well, it was a nice conversation :) . And I managed to find a source on an theoretical engine that I'd never heard before:
http://www.niac.usra.edu/files/studies/ ... rchese.pdf
As well as revise my info on the pulsed NTR concept (closest thing we have to an actual torchship).
A word of caution though: almost every engine requires radiators. Even the dusty plasma/FFRE (it's only about 50 percent efficient). Only high performance one that does not is the magneto inertial fusion engine:
http://www.projectrho.com/public_html/r ... ial_Fusion

I take my hat off to you, sir!


Mon Sep 03, 2018 9:49 am
Profile
User avatar

Joined: Sat Mar 05, 2011 6:24 am
Posts: 398
Post Re: The "Real Aerospace" Thread
Mr.Tucker wrote:
Ah, Mjolnir, I see you too are amn of engines :D

Admittedly I was trying to calculate powers of ten at 01.00 AM, so I messed up. The isp is waaaay too high. Muh bad...

In my mind there is a hierarchy of engines: you start with chemical, proceed to solid core NTR (such as NERVA; the only reason we ain't using them right now in space is because of politics),then pulsed NTR (which has an Isp of about 17.000 sec) and the next logical step is nuclear electric. Standard NEP is having a reactor drive an engine and a propellant tank that is separate. The concept I was going for was to have the reactor do double duty, and act as both power source and reaction mass. Though separating the xenon from the salt would still require mass, which may offset any gains I get from saving on reaction mass.

Ah well, it was a nice conversation :) . And I managed to find a source on an theoretical engine that I'd never heard before:
http://www.niac.usra.edu/files/studies/ ... rchese.pdf
As well as revise my info on the pulsed NTR concept (closest thing we have to an actual torchship).
A word of caution though: almost every engine requires radiators. Even the dusty plasma/FFRE (it's only about 50 percent efficient). Only high performance one that does not is the magneto inertial fusion engine:
http://www.projectrho.com/public_html/r ... ial_Fusion

I take my hat off to you, sir!


Well, molten salt reactors aren't the only way to do the job. Zubrin's nuclear saltwater rockets inject the fissile material into a reaction chamber as a salt solution, with the products directly exhausted as high temperature plasma. No xenon extraction required, you just need to build a reaction chamber and nozzle that can handle a continuous torrent of nuclear fire. And keep neutron reflectors away from your propellant tanks. And never ever spring a propellant leak.

As for Blacklight, Mills is a fraud that's been selling his free energy scheme since the early 1990s. Blacklight Power goes by "Brilliant Light Power" these days, probably because Mills had been "about to release commercial products" based on hydrino technology for over 2 decades under the previous name.


Mon Sep 03, 2018 1:00 pm
Profile
User avatar

Joined: Tue Oct 29, 2013 9:45 am
Posts: 215
Post Re: The "Real Aerospace" Thread
Oh, I know the man's a fraud. But doctor Marchese's study helped shed light on exactly how they calculate things. Even if said things make no sense physically. Just goes to show ya NASA DOES investigate all manner of claims seriously.

As for doctor Zubrin's... uhmmm...nuclear candle....well, when I first read of it 15 years ago, I thought it was crazy. Today...I still think it is. Doesn't help that the good doctor seems to have a vendetta against VASIMR (which, while not the best, is still the ONLY game in town in terms of plasma propulsion; we really need a serious MPD study...).

OTOH, the research into fusion seems to have taken a turn for the better with the commercial availability of high(er?) temperature superconducting tape:
https://www.youtube.com/watch?v=4ao24BhgBKc
Those superconducting tapes seem to be applicable in many other designs such as ITER (if you could get them to be bolder and stop asking for decades of funding) and even the polywell.
If only the promise came true...


Mon Sep 03, 2018 1:34 pm
Profile
User avatar

Joined: Sat Mar 05, 2011 6:24 am
Posts: 398
Post Re: The "Real Aerospace" Thread
I'd concocted a descendant of the NSWR, the Antimatter-Catalyzed Fusion Boosted Nuclear Saltwater Rocket, which uses small amounts of antimatter to induce fusion as a neutron source to allow subcritical fissile salts to be used, in part as an exercise in stacking letters onto an acronym, and in part to propose a system that aims to improve on the safety and practicality of a NSWR by adding antimatter.

Zubrin seems to suffer from tunnel vision with respect to getting humans to Mars in the particular way he envisions (one-shot missions using Shuttle/ISS-derived expendable vehicles), and his criticism of VASIMR seems to be affected by that. VASIMR can't get humans to Mars faster than chemical propulsion with any power source we can build in the near future, and he seems to think that's the only thing that matters. But it could get bulk cargos there on longer trajectories with far less propellant mass, and it has major speed and endurance advantages when it comes to sending probes out into the belt and outer system.


Mon Sep 03, 2018 3:25 pm
Profile
User avatar

Joined: Tue Oct 29, 2013 9:45 am
Posts: 215
Post Re: The "Real Aerospace" Thread
Mjolnir wrote:
I'd concocted a descendant of the NSWR, the Antimatter-Catalyzed Fusion Boosted Nuclear Saltwater Rocket, which uses small amounts of antimatter to induce fusion as a neutron source to allow subcritical fissile salts to be used, in part as an exercise in stacking letters onto an acronym, and in part to propose a system that aims to improve on the safety and practicality of a NSWR by adding antimatter.


I would ask, if your intent is to use an antimatter catalyzed reaction, why not go straight to fusion? Or, do something similar to H-B inertial catalyzed fusion. Here's a fascinating concept:
http://www.projectrho.com/public_html/r ... nterceptor


Tue Sep 04, 2018 12:54 pm
Profile
User avatar

Joined: Sat Mar 05, 2011 6:24 am
Posts: 398
Post Re: The "Real Aerospace" Thread
Mr.Tucker wrote:
Mjolnir wrote:
I'd concocted a descendant of the NSWR, the Antimatter-Catalyzed Fusion Boosted Nuclear Saltwater Rocket, which uses small amounts of antimatter to induce fusion as a neutron source to allow subcritical fissile salts to be used, in part as an exercise in stacking letters onto an acronym, and in part to propose a system that aims to improve on the safety and practicality of a NSWR by adding antimatter.


I would ask, if your intent is to use an antimatter catalyzed reaction, why not go straight to fusion?


It'd make the acronym shorter.
Note that the above justifications were pretty much an exhaustive list of the design goals.


Mr.Tucker wrote:
Or, do something similar to H-B inertial catalyzed fusion. Here's a fascinating concept:
http://www.projectrho.com/public_html/r ... nterceptor


Funny you specifically linked that, I've discussed the ACFBNSWR with Elukka before, and the rather more serious microfission/fusion pulse drive proposals that inspired it.


Tue Sep 04, 2018 3:06 pm
Profile
Display posts from previous:  Sort by  
Reply to topic   [ 485 posts ]  Go to page Previous  1 ... 16, 17, 18, 19, 20

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group.
Designed by STSoftware for PTF.