SWAG 25,00 kg.93143 wrote:How heavy would a 50 MW space reactor be?
http://www.astronautix.com/articles/sovctric.htm
http://en.wikipedia.org/wiki/Nuclear_thermal_rocket
White House Decides to Outsource NASA Work
-
kunkmiester
- Posts: 892
- Joined: Thu Mar 12, 2009 3:51 pm
- Contact:
self assembly modules aren't hard to design. Rendezvous in orbit isn't hard, we've been doing it for decades. Design the modules to screw together. Now all you need is a maneuvering unit and reaction mass. The module can carry that, and the maneuvering unit can be reused. Rendezvous, the MU gets them lined up, and spins them together. Once assembled and pressurized, the astronauts would go through and plug in the electronics and stuff. For something like the ISS's trestle, quick latch attachments could be used, with a brief spacewalk or two to put in permanent bolts when it's time.
I'd see a Mars mission as large. You'd ahve a large orbiter, with technicians to control a bunch of robots sent wherever they like--with the advantage of real time control. Several manned landings would be supported as well, so you're looking at possibly over a dozen people. That's a very large ship. Even with heavies, you'll need multiple launches. The same ship would be designed for multiple uses, possibly being reconfigured for asteroid missions or something.
I will concede that it would take a significantly cheaper small vehicle to make much orbital assembly practical, and a heavy launcher would mitigate that to some extent. I think orbital assembly is mostly a time and mass issue though, and not technical.
It's debatable if NASA is even needed for research. aside from bureaucratic stupidity and bungling as a few examples have mentioned, I'm sure that private universities could find much more efficient ways to do research. This is very easy. A bunch of universities shouldn't have trouble designing a bit of a publicity campaign, and then most Congress Critters have a school of some sort in their district/state, and it's very hard to ignore PhD's, especially when the other side's can be dismissed as bureaucrats.
Would an orbital observatory be any less useful if it was made by a coalition of universities rather than NASA? Would it be any more expensive? Would NASA really be able to do anything if almost every critter in Congress was being threatened by their local institution?
I'd see a Mars mission as large. You'd ahve a large orbiter, with technicians to control a bunch of robots sent wherever they like--with the advantage of real time control. Several manned landings would be supported as well, so you're looking at possibly over a dozen people. That's a very large ship. Even with heavies, you'll need multiple launches. The same ship would be designed for multiple uses, possibly being reconfigured for asteroid missions or something.
I will concede that it would take a significantly cheaper small vehicle to make much orbital assembly practical, and a heavy launcher would mitigate that to some extent. I think orbital assembly is mostly a time and mass issue though, and not technical.
It's debatable if NASA is even needed for research. aside from bureaucratic stupidity and bungling as a few examples have mentioned, I'm sure that private universities could find much more efficient ways to do research. This is very easy. A bunch of universities shouldn't have trouble designing a bit of a publicity campaign, and then most Congress Critters have a school of some sort in their district/state, and it's very hard to ignore PhD's, especially when the other side's can be dismissed as bureaucrats.
Would an orbital observatory be any less useful if it was made by a coalition of universities rather than NASA? Would it be any more expensive? Would NASA really be able to do anything if almost every critter in Congress was being threatened by their local institution?
Evil is evil, no matter how small
Yep.Skipjack wrote:That is why NASA should be funding more research in this area.think that without Polywell (or equivalent) we are stuck on Earth or near abouts.
Fund everythjng, FRC, Polywell, ME, etc, all of these potentially enabling technologies. If only one thing pays off...
Engineering is the art of making what you want from what you can get at a profit.
And Quicklaunch, Inc. is one of them.MSimon wrote:Yep.Skipjack wrote:That is why NASA should be funding more research in this area.think that without Polywell (or equivalent) we are stuck on Earth or near abouts.
Fund everythjng, FRC, Polywell, ME, etc, all of these potentially enabling technologies. If only one thing pays off...
Aero
As long as it will TRULY be commercial, i.e., free enterprise; and not like the "commercial" wholey owned subsidiaries of the Navy like Bath Iron Works, Northrup Grumman Ship Building, Electric Boat Company... I fear that it will not be truly commercial. I hope that it will.Josh Cryer wrote: As far as Heavy Lift is concerned, they're saying it's going to be commercial. I don't know if I like this idea. But if a company can come up with an Ares V or equivalent I am happy.
Putting the whole of NASA into the commercial sector *has* been something Libertarians have been begging for, for, well, decades. I guess we can try it out!
What funding has NASA provided for Polywell??? the inquiring public wants to know!Skipjack wrote:think that without Polywell (or equivalent) we are stuck on Earth or near abouts.
That is why NASA should be funding more research in this area.
Fund everythjng, ..., Polywell, ..., etc, all of these potentially enabling technologies. If only one thing pays off...
Pretty much. It is more expensive, and the end product is heavier and less reliable, but we do know how to do it. The time issue is significant, though; not counting the stand down, it has taken us nearly a decade to construct the ISS using the heaviest launcher we have (STS). A Mars mission would be larger, meaning a vast increase in flight rate would be required to support one in a reasonable time frame. I doubt both EELVs combined could do it in less than a year even at full throttle, and launching that fast would be begging for an accident...kunkmiester wrote:I will concede that it would take a significantly cheaper small vehicle to make much orbital assembly practical, and a heavy launcher would mitigate that to some extent. I think orbital assembly is mostly a time and mass issue though, and not technical.
No, universities are best at small-scale basic research. Full-scale technology development and comprehensive technological experimentation (see NACA) are better done by a large, well-funded government agency. The academic community is too fragmented, and most of the actual researchers are doing one-man four-year Ph.D. programs, which screws up the research dynamic for large projects...It's debatable if NASA is even needed for research. aside from bureaucratic stupidity and bungling as a few examples have mentioned, I'm sure that private universities could find much more efficient ways to do research. This is very easy. A bunch of universities shouldn't have trouble designing a bit of a publicity campaign, and then most Congress Critters have a school of some sort in their district/state, and it's very hard to ignore PhD's, especially when the other side's can be dismissed as bureaucrats.
Seriously, you should see our group's CFD code. It's a train wreck; the core Navier-Stokes module doesn't even work, but no one cares because we all write our own modules anyway...
Do you mean 2500 or 25,000? Is shielding included? Power generation subsystems?MSimon wrote:SWAG 25,00 kg.
BTW I meant 50 MWe...
25,000 kg.
50 MWth fission plant.
If you want electricity the mass goes way up. Radiators.
Which says. Polywell. FRC. Or maybe FF. Direct conversion eliminates a LOT of the radiators. And the heat can get rejected at 600 K. So at T^4 your radiator size goes down by a factor of 16 roughly vs 300K. And since you are only rejecting 1/4 to 1/3 of your 50MWf it gets really good.
50 MWth fission plant.
If you want electricity the mass goes way up. Radiators.
Which says. Polywell. FRC. Or maybe FF. Direct conversion eliminates a LOT of the radiators. And the heat can get rejected at 600 K. So at T^4 your radiator size goes down by a factor of 16 roughly vs 300K. And since you are only rejecting 1/4 to 1/3 of your 50MWf it gets really good.
Engineering is the art of making what you want from what you can get at a profit.
Thanks.
I wonder how hot you could plausibly get the cooling loop of a direct conversion Polywell, if you used an exotic cooling system designed specifically to maximize the radiator temperature at all costs. Would you run into problems with enhanced sputtering from alpha impingement? Unsurmountable issues with thermal expansion?
1200 K? 1500? 1800? Maybe not...
It's a real pain to have to waste power on a heat pump just so I can use a spaceplane's wings as radiators... but Bussard assumed a cooling temperature of 1800°C, or 2073.15 K for at least some of his calculations... I wonder what made him say that...
A pair of wings with a total (top+bottom) usable radiator area of 3600 m^2 (about triple the size of a 747's wings) could dissipate 3 GW of waste heat at 2000 K, which is probably adequate for two 6 GW cores at full power. But if the heat has to come up from 600 K, about three-quarters of that would be pumping power, meaning the actual cooling power is only enough to support about a 3 GW core... hang on; there's no power left!
...
I wonder how hot you could plausibly get the cooling loop of a direct conversion Polywell, if you used an exotic cooling system designed specifically to maximize the radiator temperature at all costs. Would you run into problems with enhanced sputtering from alpha impingement? Unsurmountable issues with thermal expansion?
1200 K? 1500? 1800? Maybe not...
It's a real pain to have to waste power on a heat pump just so I can use a spaceplane's wings as radiators... but Bussard assumed a cooling temperature of 1800°C, or 2073.15 K for at least some of his calculations... I wonder what made him say that...
A pair of wings with a total (top+bottom) usable radiator area of 3600 m^2 (about triple the size of a 747's wings) could dissipate 3 GW of waste heat at 2000 K, which is probably adequate for two 6 GW cores at full power. But if the heat has to come up from 600 K, about three-quarters of that would be pumping power, meaning the actual cooling power is only enough to support about a 3 GW core... hang on; there's no power left!
...
If you get most of your energy out as direct conversion you can reject heat at what ever temp is convenient.93143 wrote:Thanks.
I wonder how hot you could plausibly get the cooling loop of a direct conversion Polywell, if you used an exotic cooling system designed specifically to maximize the radiator temperature at all costs. Would you run into problems with enhanced sputtering from alpha impingement? Unsurmountable issues with thermal expansion?
1200 K? 1500? 1800? Maybe not...
It's a real pain to have to waste power on a heat pump just so I can use a spaceplane's wings as radiators... but Bussard assumed a cooling temperature of 1800°C, or 2073.15 K for at least some of his calculations... I wonder what made him say that...
A pair of wings with a total (top+bottom) usable radiator area of 3600 m^2 (about triple the size of a 747's wings) could dissipate 3 GW of waste heat at 2000 K, which is probably adequate for two 6 GW cores at full power. But if the heat has to come up from 600 K, about three-quarters of that would be pumping power, meaning the actual cooling power is only enough to support about a 3 GW core... hang on; there's no power left!
...
And to use a heat pump is going to be tricky.
SSTO you use reaction mass for cooling. Once in orbit a lot less than 6 GWf is required to run your main engines. No need for 1 G acceleration. .01 G is probably fine.
You don't want to run your Polywell too hot because cooling the magnets is going to cost you.
Engineering is the art of making what you want from what you can get at a profit.
This crosses post with the "favorite novel" thread. David Brin's first novel was "Sundiver", which featured an exploration ship capable of operating in the Sun's photosphere. Crewed. Heckuva good read.
To deal with the heat load, the heat pump/radiator was an x-ray laser.
In that environment it is not so much what radiator temperature is convenient, but what radiator temperature is left.
To deal with the heat load, the heat pump/radiator was an x-ray laser.
In that environment it is not so much what radiator temperature is convenient, but what radiator temperature is left.
Low-Isp operation is nice that way - though you do have to watch your propellant use; high coolant temperature is good for that. Airbreathing is even nicer (you don't have to get all your thrust from the coolant stream). I'm actually hoping to get an engine mode (below maybe Mach 3) that uses a heat exchanger to dump waste heat into the engines. Unlimited loiter capability, unlimited range, and it's still technically regeneratively cooled...MSimon wrote:SSTO you use reaction mass for cooling.
Heh... that depends on how big your spaceship is. For a 3000 mT vehicle (about the fueled weight of a Saturn V), 6 GWf ~ 4.5 GW jet power (optimistically), Isp = 3000 s gives you 0.01 gee...Once in orbit a lot less than 6 GWf is required to run your main engines. No need for 1 G acceleration. .01 G is probably fine.
The reason it's so big is that I'm not willing to leave the cores completely unshielded, and there is thus a significant mass bonus for clustering them. This beast has eight 6 GW cores, and it needs all of them to push itself off Mars...
Maybe I'm being too stubborn about this shielding thing... or the single-stage-to-anywhere thing... or both...
Also, I suspect I'm off topic.
Fancy... I should read that...Tom Ligon wrote:To deal with the heat load, the heat pump/radiator was an x-ray laser.
Last edited by 93143 on Tue Mar 02, 2010 8:26 pm, edited 1 time in total.