Thermonuclear Steam "Rocket" Engine

[AtomicTech]

I saw this on the Orbiter Forum and wanted to bring it here:

http://neofuel.com/index_neofuel.html

Question: When you have plenty of water, just none to waste, how do you use it best? Do you use electricity and electrolysis to make hydrogen and oxygen gas? Do you make liquid hydrogn and liquid oxygen rocket fuel and use it in a known, highly reliable RL-10 family of rocket engines that really performs well?

Or, do you just use it in a simple nuclear heated steam rocket, which performs poorly regarding rocket exhaust velocity, but delivers payloads in massive amounts when the mission delta_V is less than about 3 km/second?

Answer: Simple wins. The original work expected to find water on the moon, and to have access tp perfected, advanced nuclear heated steam rockets. This story would have a much better ending if there were water on the moon, and especially on something with 100 times less gravity, instead of the moon.

The breakthrough that makes this topic relevant is that the United States space research recently (from about 2000 thru 2011) found more than 8000 objects classified as "near Earth." (near Earth Objects, NEOs).  About 1200 can be easier to get to than landing on the moon. And, the NEO's low gravity lets the landing craft launch about 100 times more weight off the NEO than launching from the moon. By comparison, the moon's gravity is "large".  The technical paper tells why we thought using water as the rocket fuel reaction mass was better than using liquid hydrogen and liquid oxygen rockets for this mission.

For me the answer is RL-10 all the way!

But I digress, I'd like to hear y'all's take on this idea.

[DDE]

Screw both of that. You can use a Solar Moth to get nuclear-like performance without using the N-word.

[AtomicTech]

Just now, DDE said:

N-word.

wdym?

[DDE]

12 minutes ago, AtomicTech said:

wdym?

Spoiler

 

[magnemoe]

Highest performance would probably be an nerva with an oxygen afterburner. An nuclear steam rocket could have way higher trust but you would get the issue of water spitting into hydrogen and oxygen and then later combine if you tried to push the isp to hard here. The split water and burn hydrolox is not that much worse and has the benefit of only using well known technology., 
The solar moth probably has the highest isp as you are not cooling something as complex as an nuclear reactor and you can kill the heating in less than an second but trust will be low unless you have mega structure mirrors. 

[NFUN]

you should read Seveneves

[Davi SDF]

Perhaps mix the water with nuclear salts so you can have a Nuclear Salt Water rocket engine? Sure, it's radioactive as frick, but you get great thrust and isp, you could send a Jupiter/Calisto mission from the Moon with such fuel!

[wumpus]

On 2/15/2022 at 12:57 PM, magnemoe said:

Highest performance would probably be an nerva with an oxygen afterburner. An nuclear steam rocket could have way higher trust but you would get the issue of water spitting into hydrogen and oxygen and then later combine if you tried to push the isp to hard here. The split water and burn hydrolox is not that much worse and has the benefit of only using well known technology., 
The solar moth probably has the highest isp as you are not cooling something as complex as an nuclear reactor and you can kill the heating in less than an second but trust will be low unless you have mega structure mirrors. 

Feeding a nerva water will net a lower Isp than a chemical hydrolox engine (presumably a solar moth could go a little higher, but not much more).  You could split the water with a nuclear reactor (or slowly with PV solar), and then feed the oxygen first and then the hydrogen to your NTR (or solar moth).  Of course, the real question would be how much water was available: you might not care about the efficiency and simply load up with more water and not have to deal with fuel lines that need to deal with pure hydrogen and/or pure (extremely hot) oxygen.

[4D4850]

Here's my take on it (where the only available propellant is water):

1. Use electrolysis to split the water.
2. Cool the products into liquid hydrogen and liquid oxygen
3. Pass them over separate nuclear reactors
4. Burn them in a combustion chamber
5. pass the exhaust over another nuclear reactor,

 

Some (probably incorrect) back-of-the-napkin math shows this would get a specific impulse around 1250.

Edited March 13, 2022 by 4D4850
Added more information.

[jimmymcgoochie]

3 hours ago, 4D4850 said:

Here's my take on it (where the only available propellant is water):

1. Use electrolysis to split the water.
2. Cool the products into liquid hydrogen and liquid oxygen
3. Pass them over separate nuclear reactors
4. Burn them in a combustion chamber
5. pass the exhaust over another nuclear reactor,

 

Some (probably incorrect) back-of-the-napkin math shows this would get a specific impulse around 1250.

I really don’t think that you’d want to put liquid oxygen into a nuclear reactor, hot oxygen is very reactive and will try its best to destroy everything it touches which in a nuclear reactor is never good.

And why so many layers of complexity? What does feeding the already very hot steam coming from two reactors and a combustion chamber, with small quantities of up burnt hydrogen/oxygen depending on mixture ratios, into yet another nuclear reactor do, besides create more superheated oxygen to react with another reactor’s delicate innards? Steam decomposes well below the temperatures of a typical NTR reactor so in the end you’re just using a reactor to un-burn the hydrogen you just burnt earlier.

[4D4850]

Just now, jimmymcgoochie said:

I really don’t think that you’d want to put liquid oxygen into a nuclear reactor, hot oxygen is very reactive and will try its best to destroy everything it touches which in a nuclear reactor is never good.

And why so many layers of complexity? What does feeding the already very hot steam coming from two reactors and a combustion chamber, with small quantities of up burnt hydrogen/oxygen depending on mixture ratios, into yet another nuclear reactor do, besides create more superheated oxygen to react with another reactor’s delicate innards? Steam decomposes well below the temperatures of a typical NTR reactor so in the end you’re just using a reactor to un-burn the hydrogen you just burnt earlier.

Whoops, I forgot about the whole 'Oxygen oxidizes things' situation. To be honest, it was just an attempt to squeeze out as much exhaust velocity as I could. 

[sevenperforce]

18 hours ago, 4D4850 said:

Here's my take on it (where the only available propellant is water):

1. Use electrolysis to split the water.
2. Cool the products into liquid hydrogen and liquid oxygen
3. Pass them over separate nuclear reactors
4. Burn them in a combustion chamber
5. pass the exhaust over another nuclear reactor,

 

Some (probably incorrect) back-of-the-napkin math shows this would get a specific impulse around 1250.

I don’t think the math on this works, even setting aside the issue of hot oxygen in your reactor. Preheating your propellants doesn’t raise your final combustion temperature significantly higher than it would already be, and since your specific impulse is dependent (to a first order) on combustion temperature, you’re not really gaining anything. 

[Nuke]

i like the idea of a nuclear engine that can refuel anywhere. if you are at mars tank up with co2, out in the kuiper belt, grab some ammonia ice, water ice at saturn, hydrocarbons at titan, etc. grab whatever remass you can get. you may get better isp with some fuels than others. but so long as you have enough remass to make it to your next rendezvous you can stay flying.

[4D4850]

On 3/14/2022 at 8:13 AM, sevenperforce said:

I don’t think the math on this works, even setting aside the issue of hot oxygen in your reactor. Preheating your propellants doesn’t raise your final combustion temperature significantly higher than it would already be, and since your specific impulse is dependent (to a first order) on combustion temperature, you’re not really gaining anything. 

As I said, my math was probably wrong. I just assumed all the velocities would add together additively, and for the injecting the propellants I just used a weighted average and assumed the exhaust velocity for O2 in a nuclear engine would be in the ballpark of 4000 m/s. After adding everything together, I got an exhaust velocity of around 12500 m/s, which gave a specific impulse (in seconds) of 1266.81, which I rounded down to 1250.

[sevenperforce]

13 hours ago, 4D4850 said:

As I said, my math was probably wrong. I just assumed all the velocities would add together additively, and for the injecting the propellants I just used a weighted average and assumed the exhaust velocity for O2 in a nuclear engine would be in the ballpark of 4000 m/s. After adding everything together, I got an exhaust velocity of around 12500 m/s, which gave a specific impulse (in seconds) of 1266.81, which I rounded down to 1250.

Yeah you can’t do that. Velocity doesn’t scale proportionally to specific energy. You’ve got to sum the energies first, figure out what kind of chamber pressures you can handle, and go from there.

If you don’t want to do all that math then you can approximate by saying that velocity scales with the square root of specific energy. 

[imcute]

talking about ksp?why think of radioactivity and polution?there is no such thing in ksp

[NFUN]

1 hour ago, imcute said:

talking about ksp?

no

[Gargamel]

Some posts have been removed.

While the main focus of the forum is KSP, this sub forum is dedicated, as the title says, to science and spaceflight, in particular S&S that doesn't pertain to KSP.  Please take KSP related discussion to the appropriate sub forum. 

If you have a problem with another user's post, then use the report function for that post.   Please do not deride another's comments. 

Edited June 23, 2022 by Gargamel

[magnemoe]

On 3/15/2022 at 2:53 AM, Nuke said:

i like the idea of a nuclear engine that can refuel anywhere. if you are at mars tank up with co2, out in the kuiper belt, grab some ammonia ice, water ice at saturn, hydrocarbons at titan, etc. grab whatever remass you can get. you may get better isp with some fuels than others. but so long as you have enough remass to make it to your next rendezvous you can stay flying.

Agree, more so if you accept bad ISP simply as you only need to get to the next target as you do with an ship who can mine fuel in KSP. 
And read an very interesting article at http://www.projectrho.com/, have an nuclear engine who you fly up and dock to the ship. 
You can then undock it and leave it in orbit and pick up for the next mission. 
More crazy you could undock it after injection burn, move it some km behind the ship just to bring it back for the burn into orbit, an idea for KSP 2