Nuclear powered SABRE engines

[Spaceception]

The name says it all, we've had nuclear powered air engines, and nuclear powered rocket engines, so how hard would it be to combine the two, and how powerful would it be with our current knowledge of nuclear physics?

 

Btw, this is for my book idea, but I'm not restricting it to just that.

Edited March 14, 2016 by Spaceception

[sevenperforce]

So...Project Pluto, but with a fuel tank?

Could work.

[Spaceception]

Just now, sevenperforce said:

So...Project Pluto, but with a fuel tank?

Could work.

Yeah, pretty much, but how powerful would it be? I don't need it to be Saturn V powerful or whatever, just powerful enough to get to geostationary orbit.

Edited March 14, 2016 by Spaceception

[sevenperforce]

17 minutes ago, Spaceception said:

Yeah, pretty much, but how powerful would it be? I don't need it to be Saturn V powerful or whatever, just powerful enough to get to geostationary orbit.

With nuclear power the weight of extra propellant isn't going to be much more than the weight of a ram-air augmentation system.

[Spaceception]

Just now, sevenperforce said:

With nuclear power the weight of extra propellant isn't going to be much more than the weight of a ram-air augmentation system.

So... About as powerful as the jets and rockets today?

[Jovus]

25 minutes ago, Spaceception said:

The name says it all, we've had nuclear powered air engines, and nuclear powered rocket engines, so how hard would it be to combine the two, and how powerful would it be with our current knowledge of nuclear physics?

 

Btw, this is for my book idea, but I'm not restricting it to just that.

Book response: sure, seems plausible. You'd probably get markedly improved I_sp in both modes, too.

Real response: show me a working SABRE engine first.

[Spaceception]

Just now, Jovus said:

Book response: sure, seems plausible. You'd probably get markedly improved I_sp in both modes, too.

Real response: show me a working SABRE engine first.

Would Skylon as a model suffice?

[Jovus]

Has it flown yet? Not to my knowledge, but perhaps I and Wikipedia missed something.

Don't get me wrong; I'm not saying it won't work. I'm saying we don't know if it will work until they actually put it to the test. (And not just ground-based firings, though that would at least help.)

[fredinno]

37 minutes ago, Spaceception said:

The name says it all, we've had nuclear powered air engines, and nuclear powered rocket engines, so how hard would it be to combine the two, and how powerful would it be with our current knowledge of nuclear physics?

 

Btw, this is for my book idea, but I'm not restricting it to just that.

No, horrible idea, NTRs have too low TWR and are too heavy. http://selenianboondocks.com/2010/06/ssto-ntr-bad/

IRL isn't ksp.

[Spaceception]

Just now, Jovus said:

Has it flown yet? Not to my knowledge, but perhaps I and Wikipedia missed something.

Don't get me wrong; I'm not saying it won't work. I'm saying we don't know if it will work until they actually put it to the test. (And not just ground-based firings, though that would at least help.)

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

Just now, fredinno said:

No, horrible idea, NTRs have too low TWR and are too heavy. http://selenianboondocks.com/2010/06/ssto-ntr-bad/

IRL isn't ksp.

Awww, I was hoping for a cool SSTO.

I guess I'll settle for a regular SSTO

[FreeThinker]

Yes, it would be realy powerful. When fitted with Electric Generator and Electric prpulsion, you could build a SSTO directly to mars and back . The only big problem it they tend to leak radiation. So until we get desperate enough to go there, no SSTO mars trip. In the mean time you can try you luck in KSPI-E

Edited March 14, 2016 by FreeThinker

[Kerbart]

This is the kind of technology where concepts are easy and execution is terribly, terribly hard.

Added difficulty is that when you spend millions and millions on the technology and you get it finally to work after many years or even decades, some lawyer will come along and point out that you have "stolen" their technology (concept) that they patented while you were working hard on actually making it work. But I digress...

[Nuke]

i think the place for the reactor in this case is on the ground, splitting water, and cooling the resulting gasses so we can have rocket fuel.

skylon is going to be doing the job of ferrying stuff from the surface to leo and back. it does not need a reactor to do this.

Edited March 14, 2016 by Nuke

[Nibb31]

17 hours ago, Spaceception said:

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

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.

17 hours ago, Spaceception said:

Awww, I was hoping for a cool SSTO.

I guess I'll settle for a regular SSTO

SSTO has a silly payload fraction. If you add reusability and landing equipment, then you get a negative payload fraction. I really don't understand the appeal of SSTO other than "it looks cool".

[Spaceception]

Just now, 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.

SSTO has a silly payload fraction. If you add reusability and landing equipment, then you get a negative payload fraction. I really don't understand the appeal of SSTO other than "it looks cool".

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.

[sevenperforce]

48 minutes ago, Nibb31 said:

SSTO has a silly payload fraction. If you add reusability and landing equipment, then you get a negative payload fraction. I really don't understand the appeal of SSTO other than "it looks cool".

SSTO is the only thing that has a ghost's chance of offering complete RLV capability in less time than it would take to simply build another ELV.

An SSTO that runs on a single propellant combination without any sort of augmentation is going to have a negative payload fraction, because engines with high enough specific impulse to get you into orbit will be too heavy to get you off the ground. That's why people propose rocket-based combined-cycle engines. Unfortunately, those are all even heavier for their rated thrust than a high-specific-impulse rocket, but do not offer enough in-atmo specific impulse boost to make up for their added dry weight. SABRE might; we don't know yet for sure.

We can get a reusable SSTO with a meaningful payload fraction. We merely need one of the following:

1. A tripropellant engine which can run on a variable-ratio mixture of three different propellants (either one oxidizer and two fuels, or two oxidizers and one fuel) to produce high thrust at launch but high impulse for the orbital insertion burn.
2. A super-lightweight afterburner to inject high-thrust propellant downstream of the high-impulse engine.
3. An ultra-high-bypass ejector ramjet to achieve stupidly high specific impulse in-atmo without significant weight increases.
4. Magic.

Each of the above have their pros and cons. Option 1 is the most ideal, but the development challenges are huge and it may not be possible to achieve high efficiency. Option 2 allows you to build a more efficient engine more easily, but adds dry weight and doesn't burn the high-thrust propellant as efficiently. Option 3 is difficult to achieve in the supersonic regime without movable inlets, which makes dry weight really high. Option 4 is our best choice, but my application to Hogwarts was rejected.

[KSK]

There doesn't seem much advantage in a nuclear SABRE. The whole point of a nuclear thermal engine is that the propellant is heated by the nuclear reactor rather than by combustion. Hence they have no need for an oxidizer and therefore the whole reason for using SABRE (ability to use atmospheric air as an oxidizer) becomes moot.

I suppose you could go for a hot-air rocket that uses air as a propellant whilst in atmosphere but I don't know how efficient it would be. From a materials point of view it would be difficult since you'd need to find something that was resistant to hot oxidizing conditions and hot reducing conditions - assuming you're using LH2 or NH3 as your on-board propellant - and if you're not, then why bother with nuclear at all since most of your ISP advantage disappears with other propellants.

[fredinno]

2 hours ago, KSK said:

There doesn't seem much advantage in a nuclear SABRE. The whole point of a nuclear thermal engine is that the propellant is heated by the nuclear reactor rather than by combustion. Hence they have no need for an oxidizer and therefore the whole reason for using SABRE (ability to use atmospheric air as an oxidizer) becomes moot.

I suppose you could go for a hot-air rocket that uses air as a propellant whilst in atmosphere but I don't know how efficient it would be. From a materials point of view it would be difficult since you'd need to find something that was resistant to hot oxidizing conditions and hot reducing conditions - assuming you're using LH2 or NH3 as your on-board propellant - and if you're not, then why bother with nuclear at all since most of your ISP advantage disappears with other propellants.

Yeah, but a nuclear SABRE does not need to carry O2 at all, as it uses nuclear fuel to heat the propellant during ascent after initially using the air as oxidizer for the higher TWR during atmospheric speed boost.

[Spaceception]

Just now, fredinno said:

Yeah, but a nuclear SABRE does not need to carry O2 at all, as it uses nuclear fuel to heat the propellant during ascent after initially using the air as oxidizer for the higher TWR during atmospheric speed boost.

That's why I thought it'd be a good idea

[kunok]

3 hours ago, sevenperforce said:

A tripropellant engine which can run on a variable-ratio mixture of three different propellants (either one oxidizer and two fuels, or two oxidizers and one fuel) to produce high thrust at launch but high impulse for the orbital insertion burn.

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

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

Quote

There were 50 test burns proving the separate modes and a smooth switch between them. Energomash states that if additional investment could be found use of the engine would lead to a 10 x cut in payload launch costs and make the development of a SSTO vehicle possible (VTOVL)

 

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

 

[Clockwork_werewolf]

Actually this is not a bad idea as long as you do two things.

First is build it a bit like a plane so that it can take of and get into the upper atmo without needing a TWR of more than 1.

Second have the first stage heat air not fuel. https://en.wikipedia.org/wiki/Nuclear-powered_aircraft The idea was tested a bit for bombers and ICBM's with the idea that without fuel they could stay up for weeks or years.

With these two points the rocket would only need fuel at the point it couldn't use air any-more. I say it like that because it could be over heating that stops it's first stage burn before it runs out of air. Without using any fuels for the first stage there is no liquid to use for coolant like in the Sabre design. You might need a powered coolant link in order to ensure you got workable hight before friction overheated the core. There are many other problems with this design of course. Making the chamber good for heating air at -40 to 100 Celsius AND heating liquid hydrogen at much cooler temperatures could cause HUGE expansion problems. You would need air vents to close and open at very high speeds. You would also have to deal with nuclear lobby's and designing and building something almost only dreamt of right now. If done right and well however it could have a large payload fraction as it would be using a very high ISP engine just to get it into orbit from high altitude.

Quick idea, have the core surrounded by liquid helium being pumped in a closed circuit to fins around the engine. the fins take in air and heat it to make air thrust. at the middle ground set the openings to half size and flush the pipes with helium and start using that for thrust as well while turning to a steeper angle for exit. continue closing the vents as friction increases until you are "burning" hydrogen.

[fredinno]

13 minutes ago, Clockwork_werewolf said:

Actually this is not a bad idea as long as you do two things.

First is build it a bit like a plane so that it can take of and get into the upper atmo without needing a TWR of more than 1.

Second have the first stage heat air not fuel. https://en.wikipedia.org/wiki/Nuclear-powered_aircraft The idea was tested a bit for bombers and ICBM's with the idea that without fuel they could stay up for weeks or years.

With these two points the rocket would only need fuel at the point it couldn't use air any-more. I say it like that because it could be over heating that stops it's first stage burn before it runs out of air. Without using any fuels for the first stage there is no liquid to use for coolant like in the Sabre design. You might need a powered coolant link in order to ensure you got workable hight before friction overheated the core. There are many other problems with this design of course. Making the chamber good for heating air at -40 to 100 Celsius AND heating liquid hydrogen at much cooler temperatures could cause HUGE expansion problems. You would need air vents to close and open at very high speeds. You would also have to deal with nuclear lobby's and designing and building something almost only dreamt of right now. If done right and well however it could have a large payload fraction as it would be using a very high ISP engine just to get it into orbit from high altitude.

Quick idea, have the core surrounded by liquid helium being pumped in a closed circuit to fins around the engine. the fins take in air and heat it to make air thrust. at the middle ground set the openings to half size and flush the pipes with helium and start using that for thrust as well while turning to a steeper angle for exit. continue closing the vents as friction increases until you are "burning" hydrogen.

The TWR and high mass of NTRs kill it.

[KSK]

1 hour ago, fredinno said:

Yeah, but a nuclear SABRE does not need to carry O2 at all, as it uses nuclear fuel to heat the propellant during ascent after initially using the air as oxidizer for the higher TWR during atmospheric speed boost.

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.

 

[Kerbart]

6 hours ago, Spaceception said:

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

2034? Whatever happened with “before this decade is out”? 

[Spaceception]

Just now, Spaceception said:

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

 

Just now, Kerbart said:

2034? Whatever happened with “before this decade is out”? 

 

Like Nibb said, it would need a lot of infrastructure, but you also have to focus on the "Perhaps sometime before 2034 it'll launch" That includes 2020