NASA Keeping Nuclear-thermal Option Open For Mars

Would it be more or less efficient to go with nuclear electric propulsion that propels a plasma or ion thruster? Also, does the use of nuclear reactor necessitate the use of large radiation fins?
 
GeorgeA said:
blackstar said:
For about a year or so there have been a few articles about this subject along the lines of "NASA is doing stuff on nuclear thermal." Unfortunately, this is 99% PR and 1% reality. I think it is a case of the Glenn Research Center having a few people doing a limited amount of research and hoping that they will get funding for more. But there's no push in the NASA budget to spend the required money--which is a LOT of money. So there's no there there.
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Stan Borowski and some of the other true believers at Glenn have been analyzing pretty much every conceivable variation of the core NERVA concept…I got to meet Stan at an AIAA event at MIT right after the end of SEI. Smart guy and he graciously took the time to chat with a dweeb like me. I'll bet he would have expected to see one of his designs flying by now, sadly.
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Well, now we have a rocket that can put enough LH2 in orbit to make NTRs worthwhile. And no-methane isn’t a good choice for NTRs.
 
Anton Petrov has just posted a video about advances in nuclear Stirling engines and I'm posting it in this thread as I think it's the right one:


Hello and welcome! My name is Anton and in this video, we will talk about the steam engines powered by nuclear power Links:
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https://news.cgtn.com/news/2023-04-02...
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https://rps.nasa.gov/news/40/stirling...
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https://en.wikipedia.org/wiki/Kilopower
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https://en.wikipedia.org/wiki/Radiois...
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https://en.wikipedia.org/wiki/Stirlin...
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https://en.wikipedia.org/wiki/Stirlin...
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#stirlingengine #nuclear #spaceengine
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Also good for powersats that use working fluids-reflectors need not be PV.
 
NASA and DARPA have selected Lockheed Martin to develop a spacecraft to demonstrate nuclear propulsion technologies in Earth orbit later this decade.
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However, DRACO will be a very limited demonstration of NTP. “It’s a flying test stand, essentially,” said Dodson. After launched into an operational orbit, likely between 700 and 2,000 kilometers high, the spacecraft will not make any major maneuvers. Instead, the focus will be on the vehicle’s reactor and its use of HALEU fuel, which has not been used in nuclear reactors in space before. “This will be the primary focus of the DRACO demo, and the act of collecting data on the HALEU reactor will define mission success.”
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spacenews.com

NASA and DARPA select Lockheed Martin to develop DRACO nuclear propulsion demo

NASA and DARPA have selected Lockheed Martin to develop a spacecraft to demonstrate nuclear propulsion technologies in Earth orbit later this decade.
spacenews.com spacenews.com
 
Given the considerable difficulties in the long-term storage of LH2 for long duration flights to places such as Mars NASA would be better off in the near looking at liquid ammonia or liquid methane as reaction-mass for an NTP propelled spacecraft.
 
NMaude said:
Given the considerable difficulties in the long-term storage of LH2 for long duration flights to places such as Mars NASA would be better off in the near looking at liquid ammonia or liquid methane as reaction-mass for an NTP propelled spacecraft.
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Either one does horrible things to your exhaust velocity, though.
 
NMaude said:
Given the considerable difficulties in the long-term storage of LH2 for long duration flights to places such as Mars NASA would be better off in the near looking at liquid ammonia or liquid methane as reaction-mass for an NTP propelled spacecraft.
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I was thinking that myself - H2 is the more efficient reaction mass but harder to contain. How hard would H2 production be on mars compared CH4?
 
Scott Kenny said:
Make methane and crack it to hydrogen.
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I'm not sure what the proposed mechanism is for making methane. Presumably electrolysis of water would produce hydrogen and useful oxygen, but I've no idea if that is more or less energy intensive or how hard collection/separation would be.
 
Scott Kenny said:
Either one does horrible things to your exhaust velocity, though.
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While that's the case they are better from storage point of view as both have much higher boiling-points AND they are denser than LH2 so smaller storage-tanks.
 
My master's thesis looked at fuels for thermal rockets for manned missions to Mars. The conclusion was that H2 gave the best ISP/performance, but that CH4 was the best compromise due to being much easier to handle. If you put enough power into the reactor, you can just dissociate CH4 into carbon and hydrogen and get a significant ISP boost. NH3 isnt as good, and H2O was the worst. If you want a more exotic but workable fuel, Lithium can be used and gives decent ISP.
 
NMaude said:
While that's the case they are better from storage point of view as both have much higher boiling-points AND they are denser than LH2 so smaller storage-tanks.
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If you can get 1m/s/s out of your engines, you don't need to store hydrogen for very long, it's 11 days from Earth to Mars on a constant burn.

Crud, if you can only get 0.1m/s/s out of the engines it's all of 35 days to Mars!
 
Desertfox said:
If you put enough power into the reactor, you can just dissociate CH4 into carbon and hydrogen and get a significant ISP boost.
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A fast-neutron nuclear-reactor should be able to generate the needed heat.
 
Desertfox said:
My master's thesis looked at fuels for thermal rockets for manned missions to Mars. The conclusion was that H2 gave the best ISP/performance, but that CH4 was the best compromise due to being much easier to handle. If you put enough power into the reactor, you can just dissociate CH4 into carbon and hydrogen and get a significant ISP boost. NH3 isnt as good, and H2O was the worst. If you want a more exotic but workable fuel, Lithium can be used and gives decent ISP.
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Problem with letting reactor heat break methane into hydrogen and carbon is the carbon coking up your reactor. Ammonia would be much preferable if you're planning on breaking the remass into hydrogen and whatever.
 
Reading up on hypothetical methane production on mars, it seems to involve electrolysis of CO2 from the thin atmosphere in the presence of hydrogen…and presumably that requires hydrogen from the electrolysis of water from ice in a mars environment. So using hydrogen directly from water electrolysis would greatly simplify fuel production on mars (or any number of solar objects) on top of having the best performance. So I can see why they would want to go that route despite containment issues with H2.
 
siegecrossbow said:
Would it be more or less efficient to go with nuclear electric propulsion that propels a plasma or ion thruster? Also, does the use of nuclear reactor necessitate the use of large radiation fins?
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Nuclear thermal propulsion does not necessarily require radiator fins, much of the reactor heat goes out the exhaust.

Taking advantage of a nuclear reactor to also provide electrical power while not thrusting will require radiator fins.

Size of fins depends on power that needs to be radiated and how hot you can run that radiator. 1600K, red hot? You can get away with a small radiator (area goes down with the square of the increase in temperature). Something more like 800K? Gonna need a radiator 4x the size of the 1600K radiator, assuming the same waste heat to get rid of.
 
siegecrossbow said:
Would it be more or less efficient to go with nuclear electric propulsion that propels a plasma or ion thruster? Also, does the use of nuclear reactor necessitate the use of large radiation fins?
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An ion engine using power from a reactor is going to be far, far more efficient in terms of acceleration per kg of reaction mass. But it wouldn't necessarily save you any time on a trip to mars since they generate so little thrust (someone far smarter than me would have to do the math). The nuclear thermal rocket however would buy you much greater acceleration per unit of time, which would greatly shorten trips closer to earth (particular something as close as the moon). It also would allow for reaction mass to be processed most anywhere for refueling (see the discussion of methane or hydrogen as reaction mass). If your reaction mass is Xenon, you are going to have a much harder time finding and separating it outside of an earth environment. I think on earth noble gases are predominantly separated from natural gas deposits; certainly in the case of helium.
 
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Josh_TN said:
An ion engine using power from a reactor is going to be far, far more efficient in terms of acceleration per kg of reaction mass. But it wouldn't necessarily save you any time on a trip to mars since they generate so little thrust. The nuclear thermal rocket however would buy you much greater acceleration, which would greatly shorten trips closer to earth (particular something as close as the moon). It also would allow for reaction mass to be processed most anywhere for refueling (see the discussion of methane or hydrogen as reaction mass). If your reaction mass is Xenon, you are going to have a much harder time finding and separating it outside of an earth environment. I think on earth noble gases are predominantly separated from natural gas deposits; certainly in the case of helium.
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If ion drives (or VASIMR) can get 0.1m/s/s, that's plenty fast for anywhere inside the Belt. Saturn is about 88 days at 0.1m/s/s, Jupiter is on the order of 65 days (I need to doublecheck those halfway distances again, things get weird when you're talking about orbital mechanics).
 
Scott Kenny said:
If ion drives (or VASIMR) can get 0.1m/s/s, that's plenty fast for anywhere inside the Belt. Saturn is about 88 days at 0.1m/s/s, Jupiter is on the order of 65 days (I need to doublecheck those halfway distances again, things get weird when you're talking about orbital mechanics).
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Are we anywhere near a VASIMIR set up that could push people and equipment at 0.1 m/s? Thermal nuclear rockets were more or less worked out in the 60's; it is a pretty simple technology.
 
Josh_TN said:
Are we anywhere near a VASIMIR set up that could push people and equipment at 0.1 m/s? Thermal nuclear rockets were more or less worked out in the 60's; it is a pretty simple technology.
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Seen requests for funding them, and I'm not sure what NASA is actually planning on running for their Mars missions. Could be either VASIMR or a nuke-thermal rocket or just a beefy ion drive.
 
Josh_TN said:
An ion engine using power from a reactor is going to be far, far more efficient in terms of acceleration per kg of reaction mass. But it wouldn't necessarily save you any time on a trip to mars since they generate so little thrust (someone far smarter than me would have to do the math).
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I've put together a spreadsheet for constant-acceleration travel time, using the formulas from Atomic Rockets, PM me your email, I'll send it as an XLSX. Forum won't let me attach a spreadsheet.
 

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