Nuclear powered SABRE engines

[sevenperforce]

2 hours ago, kunok said:

You talk like there isn't one already https://en.wikipedia.org/wiki/RD-701

http://www.astronautix.com/engines/rd701.htm

It surely needs more development, maybe even a restart in the program.

I don't like LH₂. It's the death knell for virtually any chance at full reusability. I mean, if you're building an expendable upper stage with a really wide body, then by all means use LH₂. But not for an RLV.

Here's a thought -- instead of using two fuels, why not try using two oxidizers with a single fuel? The fuel would need to be dense if possible -- ethylene would be a good choice. It cokes, so it can't be used for a fuel-rich preburn, but it is denser and higher-impulse than liquid methane.

The Soyuz rockets use HTP to run their turbopumps, so there's already a lot of research in that area. HTP can be run in staged combustion mode without needing a reducer, and its density is comparable to that of LOX. At launch, use HTP/C2H4 with just a trickle of LOX, then gradually reduce the HTP flow and increase the LOX flow to decrease thrust and increase specific impulse. You can either use the HTP to run the turbopumps the entire time, or you can stage-combust the LOX as well. So you end up with just a single combustion chamber (unlike the dual combustion chambers of the RD-71) and a highly variable thrust vs specific impulse profile.

[kunok]

56 minutes ago, sevenperforce said:

I don't like LH₂. It's the death knell for virtually any chance at full reusability. I mean, if you're building an expendable upper stage with a really wide body, then by all means use LH₂. But not for an RLV.

The tanks meant for a tripropellant engine isn't that big http://www.astronautix.com/stages/makstank.htm not sure if you refer to other LH related problems.

56 minutes ago, sevenperforce said:

So you end up with just a single combustion chamber (unlike the dual combustion chambers of the RD-71)

It has two equal combustion chambers because like a lot of Russian engines have more than one combustion chamber sharing a turbopump, but every one have injectors for the two fuels and the oxidant. The rd-704 was a derived single chamber design.

Edited March 15, 2016 by kunok

[sevenperforce]

1 hour ago, kunok said:

The tanks meant for a tripropellant engine isn't that big http://www.astronautix.com/stages/makstank.htm not sure if you refer to other LH related problems.

It has two equal combustion chambers because like a lot of Russian engines have more than one combustion chamber sharing a turbopump, but every one have injectors for the two fuels and the oxidant. The rd-704 was a derived single chamber design.

The tank for the MAKS concept was small because it was air-launched. And you don't need high thrust nearly as much on an air-launched spaceplane, so why bother with the complexity of a triprop?

Anyway I also dislike LH2 because it eats through everything, making reusability hopeless.

Ah, I didn't realize that both chambers had triple injectors. That's good. Even so, bi-oxidized ethylene holds a fair bit of promise. Not sure whether the single or the double turbopumps would be the better choice. H2O2 has a fantastically high heat capacity, so it might be worth it to run everything off a single staged-combustion peroxide turbopump. Then again, I have read that ethylene won't coke below 2000 psi, which would allow triple full-flow staged combustion. Now THAT would be something. 

Best of all, I'm pretty sure catalyzed hydrogen peroxide is hypergolic with most hydrocarbons, so you don't need any ignition system. 

Come to think of it: if low-pressure ethylene won't coke, you can do better. Two preburners: a fuel-rich one, powered by catalyzed fuel-rich ethyloxide, and a pure-oxidizer one, blending peroxide and LOX in the desired ratio and catalyzing peroxide decomposition to power it. FFSC with only two injectors, since the oxidizer ratio is varied in the preburner. 

That would be one sick rocket engine. 

Edited March 15, 2016 by sevenperforce

[Steel]

On 14/03/2016 at 7:57 PM, Spaceception said:

No,, but it's supposed to fly in 2020 I believe.

 

21 hours ago, Nibb31 said:

For it to fly in 2020, they would need to be building the factories, selecting suppliers, and having completed most of the design work. Do you have any idea how much time it takes to pull off a major aerospace project like this?

Just getting the construction paperwork for a spaceport in the UK is going to take the best part of a decade.

No way is it going to fly in the next 10 years.

To add to Nibb's point, let's just bear in mind that (AFAIK) the only part of the engine that's been built and tested to date is a precooler, with no full engine firings scheduled between now and 2020 (or even at all from what I can see), probably due to the fact that most parts are still in the R&D stage.

Edited March 16, 2016 by Steel

[Hannu2]

21 hours ago, Spaceception said:

Well, that's what I heard last, but I could be wrong, perhaps sometime before 2034 it'll launch.

I didn't mean "Looking cool" just having a unique engine to boost it where it needs to go.

No, I do not think so. Popularity of nuclear power is very low and decreasing all around the world. Therefore it is nearly impossible that we will get politicians willing to release practical ban of nearly all nuclear technology in foreseeable future. It means generations, 30-50 years. Maybe more. There was some primitive investigation of nuclear propulsion in 60s. It told that it would probable be technically and economically possible. But we can only guess what would be actual limits on nuclear technology. Or what would be true environmental risks of using nuclear powered crafts in atmosphere.

I am not sure if atmospheric nuclear vehicles will ever be a good idea but extreme negative prestige of nuclear technology is very unfortunate thing because fission powered electric propulsion would have so obvious advantages in manned and unmanned research of solar system.

[fredinno]

20 hours ago, sevenperforce said:

The tank for the MAKS concept was small because it was air-launched. And you don't need high thrust nearly as much on an air-launched spaceplane, so why bother with the complexity of a triprop?

Anyway I also dislike LH2 because it eats through everything, making reusability hopeless.

Ah, I didn't realize that both chambers had triple injectors. That's good. Even so, bi-oxidized ethylene holds a fair bit of promise. Not sure whether the single or the double turbopumps would be the better choice. H2O2 has a fantastically high heat capacity, so it might be worth it to run everything off a single staged-combustion peroxide turbopump. Then again, I have read that ethylene won't coke below 2000 psi, which would allow triple full-flow staged combustion. Now THAT would be something. 

Best of all, I'm pretty sure catalyzed hydrogen peroxide is hypergolic with most hydrocarbons, so you don't need any ignition system. 

Come to think of it: if low-pressure ethylene won't coke, you can do better. Two preburners: a fuel-rich one, powered by catalyzed fuel-rich ethyloxide, and a pure-oxidizer one, blending peroxide and LOX in the desired ratio and catalyzing peroxide decomposition to power it. FFSC with only two injectors, since the oxidizer ratio is varied in the preburner. 

That would be one sick rocket engine. 

H2O2 is far less efficient than O2.

8 hours ago, Hannu2 said:

No, I do not think so. Popularity of nuclear power is very low and decreasing all around the world. Therefore it is nearly impossible that we will get politicians willing to release practical ban of nearly all nuclear technology in foreseeable future. It means generations, 30-50 years. Maybe more. There was some primitive investigation of nuclear propulsion in 60s. It told that it would probable be technically and economically possible. But we can only guess what would be actual limits on nuclear technology. Or what would be true environmental risks of using nuclear powered crafts in atmosphere.

I am not sure if atmospheric nuclear vehicles will ever be a good idea but extreme negative prestige of nuclear technology is very unfortunate thing because fission powered electric propulsion would have so obvious advantages in manned and unmanned research of solar system.

It would still be dangerous though- if you go to the engine at the wrong side....

[kunok]

21 hours ago, sevenperforce said:

The tank for the MAKS concept was small because it was air-launched. And you don't need high thrust nearly as much on an air-launched spaceplane, so why bother with the complexity of a triprop?

What? It doesn't help that much.

Look at the link of maks in astronautix

Quote

releasing MAKS at 8.6 km altitude and 900 km/hr.

That's only 250m/s http://www.wolframalpha.com/input/?i=900+km%2Fhr  and 8.6 kilometre is somewhat a low pressure but it's still pretty high 0,327 bar http://www.wolframalpha.com/input/?i=8.6+km+altitude

 

I always heard about the embrittlement of structures with the LH, but I never read something serious, can someone provide with some open info? My knowledge is  principally about iron derived materials, and the "usual" car/aeronautics alloys, always in normal or high temperatures, but never in cryogenic.

 

You always take strange combinations of fuels and oxidisers, I feel that they are wrong but I have no time to relook my chemical lessons and do the math. H2O2 isn't an efficient oxidant

Edited March 16, 2016 by kunok

[sevenperforce]

32 minutes ago, fredinno said:

H2O2 is far less efficient than O2.

The isp of kerosene/peroxide is 319 s with an oxidizer/fuel ratio of 7.07, compared to 353 s for kerolox at an oxidizer/fuel ratio of 2.56. So for any case where you're replacing LOX with peroxide, you'll lose about 10% of your isp but you approximately double your T/W ratio. So if an engine can be designed to run on a variable mixture of LOX and HTP, it will be perfect for an SSTO application.

15 minutes ago, kunok said:

What? It doesn't help that much. That's only 250m/s http://www.wolframalpha.com/input/?i=900+km%2Fhr  and 8.6 kilometre is somewhat a low pressure but it's still pretty high 0,327 bar http://www.wolframalpha.com/input/?i=8.6+km+altitude

I always heard about the embrittlement of structures with the LH, but I never read something serious, can someone provide with some open info? My knowledge is  principally about iron derived materials, and then "usual" car/aeronautics alloys, always in normal or high temperatures, but never in cryogenic.

You always take strange combinations of fuels and oxidisers, I feel that they are wrong but I have no time to relook my chemical lessons and do the math. H2O2 isn't an efficient oxidant

The combination of lower pressure, higher altitude, and nonzero launch velocity results in a pretty substantial gain. Kerosene at sea level gets roughly 300 s of impulse, so that 250 m/s represents almost 10% of your launch mass right out of the gate. Plus, gravity drag is cancelled and you can use a vacuum-optimized engine bell with an initial isp of about 336 s. Due to gravity drag and lower isp, getting from 0-1 km/s takes literally twice as much propellant as getting from 250 m/s to 1 km/s if you start at 8 km up.

Individual hydrogen atoms slip through metal-metal bonds like butter. When they meet, they form H₂ molecules, which expand and form cracks. Thus, metal LH₂ tanks are pretty much strictly single-use affairs.

Yeah, I like toying around with odd fuel/oxidizer combos. Some don't work. But like I said above, the lower isp of H2O2 is compensated for by 15% higher impulse density and twice as much thrust, making it ideal for the first "stage" in a tripropellant-fueled SSTO.

[fredinno]

23 minutes ago, sevenperforce said:

The isp of kerosene/peroxide is 319 s with an oxidizer/fuel ratio of 7.07, compared to 353 s for kerolox at an oxidizer/fuel ratio of 2.56. So for any case where you're replacing LOX with peroxide, you'll lose about 10% of your isp but you approximately double your T/W ratio. So if an engine can be designed to run on a variable mixture of LOX and HTP, it will be perfect for an SSTO application.

The combination of lower pressure, higher altitude, and nonzero launch velocity results in a pretty substantial gain. Kerosene at sea level gets roughly 300 s of impulse, so that 250 m/s represents almost 10% of your launch mass right out of the gate. Plus, gravity drag is cancelled and you can use a vacuum-optimized engine bell with an initial isp of about 336 s. Due to gravity drag and lower isp, getting from 0-1 km/s takes literally twice as much propellant as getting from 250 m/s to 1 km/s if you start at 8 km up.

Individual hydrogen atoms slip through metal-metal bonds like butter. When they meet, they form H₂ molecules, which expand and form cracks. Thus, metal LH₂ tanks are pretty much strictly single-use affairs.

Yeah, I like toying around with odd fuel/oxidizer combos. Some don't work. But like I said above, the lower isp of H2O2 is compensated for by 15% higher impulse density and twice as much thrust, making it ideal for the first "stage" in a tripropellant-fueled SSTO.

Only problem is that the much lower amount of research in H2O2 engines requires much more R+D money, and even more if you want the efficient staged combustion used in SSTOs.

[sevenperforce]

1 minute ago, fredinno said:

Only problem is that the much lower amount of research in H2O2 engines requires much more R+D money, and even more if you want the efficient staged combustion used in SSTOs.

Yeah, a dual-oxidizer variable-ratio tripropellant liquid rocket engine would take a lot of R&D for sure. Thankfully, there is already a lot of experience with using HTP to run turbopumps for rocket engines, so that's a step in the right direction. 

[kunok]

1 hour ago, sevenperforce said:

Individual hydrogen atoms slip through metal-metal bonds like butter. When they meet, they form H₂ molecules, which expand and form cracks. Thus, metal LH₂ tanks are pretty much strictly single-use affairs.

But what's the rate? how much it cracks in every flight? is not like it takes a lot of time to send the spacecraft to space.

[sevenperforce]

3 minutes ago, kunok said:

But what's the rate? how much it cracks in every flight? is not like it takes a lot of time to send the spacecraft to space.

From what I've read it seems to be a pretty rapid process...not like the rocket will blow on the launch pad or anything, but reusing even once is risky. 

[Hannu2]

13 hours ago, fredinno said:

It would still be dangerous though- if you go to the engine at the wrong side....

Of course, but I do not see any reason to go to dangerous area. It is also relatively easy to avoid with proper planning (for example during docking and EVA). Landers should use chemical engines also for thrust. Ion and other electric engines are very weak.

[fredinno]

11 hours ago, Hannu2 said:

Of course, but I do not see any reason to go to dangerous area. It is also relatively easy to avoid with proper planning (for example during docking and EVA). Landers should use chemical engines also for thrust. Ion and other electric engines are very weak.

Still, apparently for the nuclear space tugs for STS, each firing would have given astronauts their yearly recommended maximum dose of radiation, even with shielding.

[kunok]

23 hours ago, sevenperforce said:

From what I've read it seems to be a pretty rapid process...not like the rocket will blow on the launch pad or anything, but reusing even once is risky. 

I don't see why reusing in short flights it will be more damaging than an upper stage to GTO which is a long flight, I should open a new thread we are derailing the thread.

[fredinno]

Oh yeah, BTW, pad and VAB processes would need to be changed enormously to make 100% sure everyone stays away from the buiness end of the engine- which also means it'd have to run without extensive maintenance.

[Hannu2]

8 hours ago, fredinno said:

Still, apparently for the nuclear space tugs for STS, each firing would have given astronauts their yearly recommended maximum dose of radiation, even with shielding.

Yes, traveling in space would surely be much more dangerous than office work. I think that humans can not advance in manned space exploration before we learn to accept risks. It should be like explorations hundreds of year ago. Kings sent many ships to expeditions until some of them returned. It would be technically possible to reduce radiation so that astronauts could stay able to work during expedition. If not, let's add little more radiation shielding to next ship. That's why I have so pessimistic view of all current space projects. All governments and space agencies lack of pioneering attitude.

But of course first applications of nuclear reactors would be probes. It would make heavy probes possible to all bodies in solar system in sane travel time (<10 years).

 

 

[DerekL1963]

1 hour ago, Hannu2 said:

It should be like explorations hundreds of year ago. Kings sent many ships to expeditions until some of them returned.

Before it can be like exploration hundreds of years ago, there has to be something worth the money and risk - with rare exceptions, folks didn't go exploring for science, or for glory, or for the sheer heck of it.   They went because if they were successful, they hoped to reap massive commercial and economic (read big, big, BIG bucks) returns from the voyages.
 

1 hour ago, Hannu2 said:

Yes, traveling in space would surely be much more dangerous than office work. I think that humans can not advance in manned space exploration before we learn to accept risks.

We do accept risks far greater than office work - what we don't do is accept stupid risks to fuel the fantasies of ill informed space enthusiasts.

Edited March 18, 2016 by DerekL1963

[wumpus]

Yet another idea trying to rescue a broken concept without looking at how it changes the big picture.

If you have a nuclear powered spaceplane, why in the world would you burn hydrogen while still in the atmosphere?  You can raise the temperature of intake air as high as you please with just nuclear, your Isp is effectively infinite (not by the official definition which only looks at exaust velocity, but more due to the fact that difference between wet and dry weight is theoretically defined by e=mc**2).

Once you leave the atmosphere, there is no reason to take along any oxygen, as the Isp of a nuclear rocket pretty much needs hydrogen to get anywhere near 800.

There is no reason to drag along *anything* that looks like a SABRE engine.  It not only would be dead weight, the fuel would *also* be dead weight.  It would be a disaster to bring such a thing along.  This is pretty much why the thread has devolved into yet another "what if the skylon (an excuse to use a SABRE) had a non-SABRE engine?" thread.

[p1t1o]

8 minutes ago, wumpus said:

Yet another idea trying to rescue a broken concept without looking at how it changes the big picture.

If you have a nuclear powered spaceplane, why in the world would you burn hydrogen while still in the atmosphere?  You can raise the temperature of intake air as high as you please with just nuclear, your Isp is effectively infinite (not by the official definition which only looks at exaust velocity, but more due to the fact that difference between wet and dry weight is theoretically defined by e=mc**2).

Once you leave the atmosphere, there is no reason to take along any oxygen, as the Isp of a nuclear rocket pretty much needs hydrogen to get anywhere near 800.

There is no reason to drag along *anything* that looks like a SABRE engine.  It not only would be dead weight, the fuel would *also* be dead weight.  It would be a disaster to bring such a thing along.  This is pretty much why the thread has devolved into yet another "what if the skylon (an excuse to use a SABRE) had a non-SABRE engine?" thread.

Agreed, in principle at least. A "nuclear powered" SABRE is not a SABRE at all, by definition.

Honestly, SKYLON [as opposed to SABRE] is really only a concept on a drawing board. The engine itself, on the other hand, is a bona-fide cutting edge attempt to get the next answer to the question of airbreathing propulsion. 

The question of airbreathing SSTO's is another question entirely. And the question of nuclear propulsion, airbreathing or otherwise, a whole other one.

[Buster Charlie]

On 3/15/2016 at 2:36 PM, KSK said:

NERVA apparently had a TWR of about 7. Which is low compared to chemical rockets but seems to compare very favourably to jet engines. With modern materials it could probably also be improved. So that atmospheric speed boost doesn't look very likely. You might as well just use a nuclear engine all the way up rather than faffing about with a SABRE. If you do need to use air as reaction mass, you'd be better off just heating it in the reactor directly.

 

I read that project tumbleweed was going to be about 30 twr, which is low for a booster stage lfo rocket,  but better than 7

18 hours ago, fredinno said:

Oh yeah, BTW, pad and VAB processes would need to be changed enormously to make 100% sure everyone stays away from the buiness end of the engine- which also means it'd have to run without extensive maintenance.

Iirc in  the 60s they built a manned robotic  maintenence  vehicle in anticipation of refueling and servicing atomic bombers,  so there is that.

 

Ah here we go. http://kotaku.com/the-real-metal-gear-5556757

Edited March 18, 2016 by Buster Charlie

[fredinno]

4 hours ago, wumpus said:

Yet another idea trying to rescue a broken concept without looking at how it changes the big picture.

If you have a nuclear powered spaceplane, why in the world would you burn hydrogen while still in the atmosphere?  You can raise the temperature of intake air as high as you please with just nuclear, your Isp is effectively infinite (not by the official definition which only looks at exaust velocity, but more due to the fact that difference between wet and dry weight is theoretically defined by e=mc**2).

Once you leave the atmosphere, there is no reason to take along any oxygen, as the Isp of a nuclear rocket pretty much needs hydrogen to get anywhere near 800.

There is no reason to drag along *anything* that looks like a SABRE engine.  It not only would be dead weight, the fuel would *also* be dead weight.  It would be a disaster to bring such a thing along.  This is pretty much why the thread has devolved into yet another "what if the skylon (an excuse to use a SABRE) had a non-SABRE engine?" thread.

Well, using 2 different fuels increases complexity, but ok, I see where you are coming from. How about using a air-breathing NTR that switches to O2 once it needs it (H2 has higher isp, but lower TWR.)

4 hours ago, Buster Charlie said:

I read that project tumbleweed was going to be about 30 twr, which is low for a booster stage lfo rocket,  but better than 7

Iirc in  the 60s they built a manned robotic  maintenence  vehicle in anticipation of refueling and servicing atomic bombers,  so there is that.

 

Ah here we go. http://kotaku.com/the-real-metal-gear-5556757

The TWR is realy the killer, but air-breathing might mitigate it enough to make nuclear SSTOs more practical

[GDJ]

On March 16, 2016 at 4:21 PM, kunok said:

But what's the rate? how much it cracks in every flight? is not like it takes a lot of time to send the spacecraft to space.

 

On March 16, 2016 at 4:25 PM, sevenperforce said:

From what I've read it seems to be a pretty rapid process...not like the rocket will blow on the launch pad or anything, but reusing even once is risky. 

Depending on the internal pressure of the tank. Lower pressures take longer (months), but if it's a high pressure tank (2000 + PSI) and the titanium isn't very thick, you're talking hours. It's a exponential increase based on pressure, amount of Hydrogen in the tank, and how thick the tank is.

 Basically, you pump it in, use it, throw it out. Even getting the hydrogen out of the Titanium alloy is a real PITA.

 

[kunok]

2 minutes ago, GDJ said:

 

Depending on the internal pressure of the tank. Lower pressures take longer (months), but if it's a high pressure tank (2000 + PSI) and the titanium isn't very thick, you're talking hours. It's a exponential increase based on pressure, amount of Hydrogen in the tank, and how thick the tank is.

 Basically, you pump it in, use it, throw it out. Even getting the hydrogen out of the Titanium alloy is a real PITA.

 

I just opened a new thread to stop derailing this and you reply me But a flight can be only a few minutes, that's why I can think of being somewhat reusable.

PD: I really hate when somebody answers me in imperial units, no offense.

[GDJ]

25 minutes ago, kunok said:

PD: I really hate when somebody answers me in imperial units, no offense.

Oh quit your whining.

Okay, I'm off the topic.