The "Real Aerospace" Thread
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Re: The "Real Aerospace" Thread
nuclear winter is extremely overhyped, why? dunno, but it is.
where do i get the balls to call something so commonly accepted bullshit? simple math, physics and history.
#1 energy, mount tambor(the volcanic eruption that caused the previously mentioned year without summer) chugged out a rough estimate for the 1815 event is ~1.4 x 10^20 joules of energy(hint, US+russian nuclear arsenal MIGHT equal that, but according to wikipedia on the subject the total throw weight of the two countries is around 9000 megatons, which is a bit short of 33000.)
<edit> might be wrong about the numbers, half asleep as i write this. </edit>
#2 dirt, that explosion happened underground throwing literaly square km of rock and ash into the atmosphere, modern nukes are airburst, to maximise destruction on the surface, incidentally this also minimises the particulate thrown into the air and following spread of irradiated matter...
which leads me to the conclusion nuclear war would probably give us a environmental hickup, might even 'skip' a summer at the most even if highly unlikely, but the decades long 'nuclear winter' is utter bullshit.
-----
on the subject of destruction of industry and infrastructure, the only thing around that could do it in 'hours' is a nuclear first strike, not enough bombs or delivery systems to do it with conventional bombs....not that it would be a fun ride even with conventional bombs, but not a industrial knockout in a few hours, or even weeks if the will to fight is there, but still i shall leave with the age old maxim "As you know, you go to war with the army you have, not the army you might want or wish to have at a later time" this perticular iteration of it comes from Donald Rumsfeld, and he might have been a douchebag but he's got a point there, probably a few he never thought of aswell.
interestingly enough as of 2016 there have been about equal numbers of F-35's and JAS 39 gripen(griffin) built, about 160 each. one of those projects cost 100 times the other, admittedly the unit cost is a bit closer at only 3x.(according to wiki) but the per hour costs brings it back up at about 10x difference, and if they spent the development cost of the f-35 on gripens they would have gotten about 30000 of'em.
yep, instead of mass producing the shit out of one model, which would be logical, they keep exploring more 'prototypes' and 'specialized models'.... morons, work horses wins wars not silver bullets.
where do i get the balls to call something so commonly accepted bullshit? simple math, physics and history.
#1 energy, mount tambor(the volcanic eruption that caused the previously mentioned year without summer) chugged out a rough estimate for the 1815 event is ~1.4 x 10^20 joules of energy(hint, US+russian nuclear arsenal MIGHT equal that, but according to wikipedia on the subject the total throw weight of the two countries is around 9000 megatons, which is a bit short of 33000.)
<edit> might be wrong about the numbers, half asleep as i write this. </edit>
#2 dirt, that explosion happened underground throwing literaly square km of rock and ash into the atmosphere, modern nukes are airburst, to maximise destruction on the surface, incidentally this also minimises the particulate thrown into the air and following spread of irradiated matter...
which leads me to the conclusion nuclear war would probably give us a environmental hickup, might even 'skip' a summer at the most even if highly unlikely, but the decades long 'nuclear winter' is utter bullshit.
-----
on the subject of destruction of industry and infrastructure, the only thing around that could do it in 'hours' is a nuclear first strike, not enough bombs or delivery systems to do it with conventional bombs....not that it would be a fun ride even with conventional bombs, but not a industrial knockout in a few hours, or even weeks if the will to fight is there, but still i shall leave with the age old maxim "As you know, you go to war with the army you have, not the army you might want or wish to have at a later time" this perticular iteration of it comes from Donald Rumsfeld, and he might have been a douchebag but he's got a point there, probably a few he never thought of aswell.
interestingly enough as of 2016 there have been about equal numbers of F-35's and JAS 39 gripen(griffin) built, about 160 each. one of those projects cost 100 times the other, admittedly the unit cost is a bit closer at only 3x.(according to wiki) but the per hour costs brings it back up at about 10x difference, and if they spent the development cost of the f-35 on gripens they would have gotten about 30000 of'em.
yep, instead of mass producing the shit out of one model, which would be logical, they keep exploring more 'prototypes' and 'specialized models'.... morons, work horses wins wars not silver bullets.
Re: The "Real Aerospace" Thread
or the more logical answer you're an arm chair quarterback who's cherry picking facts while knowing or caring little about the whole picture. let me guess you also don't believe in climate change either.... plants love CO2 right....discord wrote:nuclear winter is extremely overhyped, why? dunno, but it is.
where do i get the balls to call something so commonly accepted bullshit? simple math, physics and history.
the simple fact is even with out a nuclear winter the effect of even a small scale nuclear war would cause the collapse of the world economy. no country controls all infrastructure, knowledge or resources needed to maintain the world we live in today.
Re: The "Real Aerospace" Thread
dex: climate change is a thing, it is happening, and it is man made.... how bad is it? that I am not so sure about but not good is a pretty safe assumption though, and yes plants love co2, since oxygen is basically an inedible byproduct for them, humans and most animals however do not like more than small traces of co2 at all, at around 5-6% humanity and most animals would just be dead, thankfully we are currently around 0.04% and things would be really bad if it ever got to 1%, it has risen by a dramatic 0.02 from the previous low some 20000 years ago(normal values flow between 0.02 and 0.03, so yes we are a whole 0.01 above normal), so my guess would be that this trend will go on for a while longer, we are working on it, will probably top out at 0.05-6 which will cause some rather noticeable changes in weather patterns(which is bad enough, it fucks over farming for one, and great big honking unpredictable storms can be a nuisance), but not much else.
the one thing that might happen and would be REALLY bad(at least for me) would be the gulf stream seizing up, that would turn scandinavia into siberia.... but probably not in my lifetime though.
and on 'nuclear war is not horribad' all I really said was that none of the major countries can destroy any others industry(as in capacity to wage war) inside a day without resorting to nuclear arms, and lots of them.
fallout is a thing, and bad enough even with airbursts, however destroyed infrastructure and the collapse of transportation(and social order) thereof will probably kill more people than the actual bombs though.
am I a armchair general/scientist? probably, but I do try to not be such a bad one.
but yes, nuclear winter is pretty much bullshit, the only major difference that could possibly make up for the difference in ejected particulates(which is what caused the cooling effect in the cases of volcanoes) would be some sort of ionization of the atmosphere which would act as a radiation shield....and that sounds pretty much like technobabble to me.
if you do not believe me https://www.youtube.com/watch?v=LLCF7vPanrY visualizes it pretty well, and if that is true..... why are we not in the middle of a 'nuclear winter' right now? answer? neither enough particulates nor enough energy released.
the one thing that might happen and would be REALLY bad(at least for me) would be the gulf stream seizing up, that would turn scandinavia into siberia.... but probably not in my lifetime though.
and on 'nuclear war is not horribad' all I really said was that none of the major countries can destroy any others industry(as in capacity to wage war) inside a day without resorting to nuclear arms, and lots of them.
fallout is a thing, and bad enough even with airbursts, however destroyed infrastructure and the collapse of transportation(and social order) thereof will probably kill more people than the actual bombs though.
am I a armchair general/scientist? probably, but I do try to not be such a bad one.
but yes, nuclear winter is pretty much bullshit, the only major difference that could possibly make up for the difference in ejected particulates(which is what caused the cooling effect in the cases of volcanoes) would be some sort of ionization of the atmosphere which would act as a radiation shield....and that sounds pretty much like technobabble to me.
if you do not believe me https://www.youtube.com/watch?v=LLCF7vPanrY visualizes it pretty well, and if that is true..... why are we not in the middle of a 'nuclear winter' right now? answer? neither enough particulates nor enough energy released.
Re: The "Real Aerospace" Thread
Actually, plants use oxygen at night, which makes sense when you think about it. Read about it a few months ago.discord wrote:dex: climate change is a thing, it is happening, and it is man made.... how bad is it? that I am not so sure about but not good is a pretty safe assumption though, and yes plants love co2, since oxygen is basically an inedible byproduct for them,
Not likely, but never vote against it decisively: keep that passport updated.discord wrote:the one thing that might happen and would be REALLY bad(at least for me) would be the gulf stream seizing up, that would turn scandinavia into siberia.... but probably not in my lifetime though.
Re: The "Real Aerospace" Thread
I'd like to congratulate Elon Musk and SpaceX and celebrate the successful test launch of the Falcon Heavy.
Re: The "Real Aerospace" Thread
hi hi
You can color me impressed. I'm generally relatively skeptical about SpaceX, but that is a very big achievement. I tip my cap to all the people who worked on making it work.
You can color me impressed. I'm generally relatively skeptical about SpaceX, but that is a very big achievement. I tip my cap to all the people who worked on making it work.
- Mr Bojangles
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Re: The "Real Aerospace" Thread
Everyone and everything at my workplace just stopped so we could all watch the FH launch. Seriously impressive accomplishment; my jaw went slack at the simultaneous side booster landings.
Kudos to everyone at SpaceX.![Very Happy :D](./images/smilies/icon_e_biggrin.gif)
Kudos to everyone at SpaceX.
![Very Happy :D](./images/smilies/icon_e_biggrin.gif)
Re: The "Real Aerospace" Thread
It's a great day for Space !
They say it's gonna be playing music the whole time but I have't seen anywhere about a power source beyond the car battery. Makes me wonder if they have a couple solar cells rigged up or something.
They say it's gonna be playing music the whole time but I have't seen anywhere about a power source beyond the car battery. Makes me wonder if they have a couple solar cells rigged up or something.
- Mr Bojangles
- Posts: 283
- Joined: Sat Mar 03, 2012 1:12 am
Re: The "Real Aerospace" Thread
The whole way to Mars? I hadn't heard that, I only thought it was being powered by the booster stage's batteries.Username wrote:It's a great day for Space !
They say it's gonna be playing music the whole time but I have't seen anywhere about a power source beyond the car battery. Makes me wonder if they have a couple solar cells rigged up or something.
Re: The "Real Aerospace" Thread
Musk said in the press conference that the battery would run out in about 16 hours. Not sure specifically what he was referring to, but they definitely didn't rig up solar panels or anything like that.
Re: The "Real Aerospace" Thread
SpaceX launched (and landed) the first Block 5 Falcon 9: https://www.youtube.com/watch?v=rQEqKZ7CJlk
Lots of changes for improving reuse, and for certifying the vehicle to carry people. This should be the final version, with only minor fixes and changes moving forward. (The improved cameras were nice, but hopefully they'll fix the wobbly camera mount.)
Lots of changes for improving reuse, and for certifying the vehicle to carry people. This should be the final version, with only minor fixes and changes moving forward. (The improved cameras were nice, but hopefully they'll fix the wobbly camera mount.)
Re: The "Real Aerospace" Thread
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?
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?
Re: The "Real Aerospace" Thread
The wonders of computer controlled thrust vectoring stabilized rocketry (not fin-stabilized darts) coming to the hobby model market, inspired by the success of a particular company obviously.
The leader of that project tells about it's origin, the process of developing from a personal learning project all the way to turning the pursuit into products for sale.
Currently in development with retro-propulsive landing for the models for more advanced kits down the line.
Mastermind can be contacted here https://old.reddit.com/user/Joe-Barnard
According to this the guidance chip is all innertial (gyro) stabilized, no positioning. Right now landing back at the launch mount is not among the ambitions of the project, it would seem
https://bps.space/signal
The leader of that project tells about it's origin, the process of developing from a personal learning project all the way to turning the pursuit into products for sale.
Currently in development with retro-propulsive landing for the models for more advanced kits down the line.
Mastermind can be contacted here https://old.reddit.com/user/Joe-Barnard
According to this the guidance chip is all innertial (gyro) stabilized, no positioning. Right now landing back at the launch mount is not among the ambitions of the project, it would seem
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Re: The "Real Aerospace" Thread
Hi Jim! Your project has outlived relicnews forums! The horror. The joy!
Also in respones to previously raised criticisms about the "abominable Lightning2" project to paraphrase, "that should have been cancelled long ago" is incorrect. It's an excellent and vital weapon system for the allies going forward, a key stepping stone in the future in peer competition air power and very likely adaptable to somewhat lower intensity threat environments as well (the lowest threat environments are the place for other tools obviously.
The project has resulted in a superior product at a competitive unit price. What makes the development project catch so much hate is it's astronomical expense. And I'm not saying that this should have been tolerated as easily. However, the fact that it could have grown so expensive to develop is to a significant proportion caused by buerocratic inefficiencies and flaws. You can only lead a corrupt business in a corrupt polittical and buerocratic landscape. On the other side, making these highly complex systems integrated into this system. It's practically magic that this vehicle achieves, virtual reality gaming consoles are a recent development, this system had to exceed the capabilities of today's VR gaming consoles as an augmented reality sensor fusion weapons system yesterday! There are costs involved.
Additionally a lot of the distrust and distaste for the system is born out of human nature, it is apalling to us to have deals being struck behind closed doors, under the veil of secrecy.
The fact of the matter is, allied air forces that don't adopt these planes are likely to grow obsolete and inferior against potential adversaries.
Also, since the above mentioned model rocket company is not at liberty to export those kits, what I'm left with is either immigrating there or change careers and become a model rocket scientist.
Also in respones to previously raised criticisms about the "abominable Lightning2" project to paraphrase, "that should have been cancelled long ago" is incorrect. It's an excellent and vital weapon system for the allies going forward, a key stepping stone in the future in peer competition air power and very likely adaptable to somewhat lower intensity threat environments as well (the lowest threat environments are the place for other tools obviously.
The project has resulted in a superior product at a competitive unit price. What makes the development project catch so much hate is it's astronomical expense. And I'm not saying that this should have been tolerated as easily. However, the fact that it could have grown so expensive to develop is to a significant proportion caused by buerocratic inefficiencies and flaws. You can only lead a corrupt business in a corrupt polittical and buerocratic landscape. On the other side, making these highly complex systems integrated into this system. It's practically magic that this vehicle achieves, virtual reality gaming consoles are a recent development, this system had to exceed the capabilities of today's VR gaming consoles as an augmented reality sensor fusion weapons system yesterday! There are costs involved.
Additionally a lot of the distrust and distaste for the system is born out of human nature, it is apalling to us to have deals being struck behind closed doors, under the veil of secrecy.
The fact of the matter is, allied air forces that don't adopt these planes are likely to grow obsolete and inferior against potential adversaries.
Also, since the above mentioned model rocket company is not at liberty to export those kits, what I'm left with is either immigrating there or change careers and become a model rocket scientist.
Re: The "Real Aerospace" Thread
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.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?
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.
Re: The "Real Aerospace" Thread
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).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.
Re: The "Real Aerospace" Thread
Looking at the picture: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.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?
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.
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.
Re: The "Real Aerospace" Thread
9000 GWh = 3.24e16 J, and that diagram shows 150 kg of Xe. Aside from that:Mr.Tucker wrote:Looking at the picture: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.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?
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.
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.
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.
Re: The "Real Aerospace" Thread
Ah, Mjolnir, I see you too are amn of engines ![Very Happy :D](./images/smilies/icon_e_biggrin.gif)
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!
![Very Happy :D](./images/smilies/icon_e_biggrin.gif)
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
![Smile :)](./images/smilies/icon_e_smile.gif)
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!