Prometheus Turbo Rocket concept

[tater]

John Bucknell has pitched a partially air breathing NTR SSTO rocket in the past, but has now come up with an interesting chemical variant (still an SSTO, with an insanely high payload mass fraction) that has a mission averaged I_sp of 1600s (to LEO).

He's pushing it for orbital solar power construction (since the cost to orbit is low enough). Dunno, but a very interesting concept.

 

 

 

[kerbiloid]

The final aerobraking looks like it should be a SSTO plane with a heatshield on one side and much stronger construction than a thin fuel tank has.

Edited September 20, 2019 by kerbiloid

[tater]

38 minutes ago, kerbiloid said:

The final aerobraking looks like it should be a SSTO plane with a heatshield on one side and much stronger construction than a thin fuel tank has.

Yeah, his graphic is... not super great.

Still, it's an interesting concept (Bucknell used to work for SpaceX on Raptor, BTW).

[tater]

 

[sevenperforce]

Really interesting! I've seen the rocket blade cycle approach before. It is a troubling starting point because I feel like the materials science challenges of trying to force rocket exhaust through rotating fan blade members seems immense. You'd almost definitely run into engineering tradeoffs that would reduce your specific impulse dramatically in the pure-rocket segment of flight.

And speaking of the pure-rocket flight envelope, I think he's going to have trouble with the scramjet and film-cooled scramjet envelope. A non-combusting scramrocket is going to have slightly lower specific impulse but the drag penalty is lower and the workable envelope is wider. If he does a ramturborocket to ramjet transition and then goes to pure rocket shortly thereafter, he's going to have lower drag penalty and a lot simpler of a system. Doing that with drop tanks is probably the better approach.

It would be interesting to reimagine Skylon with this engine, drop tanks, and methalox fuel.

[tater]

His Isp numbers are mission average, as a pure rocket, it's just a rocket.

The payload mass fraction is so high, he can sacrifice performance to a huge degree, and still be insanely high (he's talking about ~40% payload mass fractions---SSTO!).

It's a fascinating concept, and the best path would be to simply build one, and see if it can actually work.

[sevenperforce]

14 minutes ago, tater said:

His Isp numbers are mission average, as a pure rocket, it's just a rocket.

The payload mass fraction is so high, he can sacrifice performance to a huge degree, and still be insanely high (he's talking about ~40% payload mass fractions---SSTO!).

It's a fascinating concept, and the best path would be to simply build one, and see if it can actually work.

Of course I would love to see someone try to build one.

It just requires a LOT of moving parts with low tolerances under extreme conditions. You can have dry mass growth or slightly lower performance and not run into problems, true, but the tolerances and flight conditions are non-negotiable.

[tater]

19 minutes ago, sevenperforce said:

Of course I would love to see someone try to build one.

It just requires a LOT of moving parts with low tolerances under extreme conditions. You can have dry mass growth or slightly lower performance and not run into problems, true, but the tolerances and flight conditions are non-negotiable.

Absolutely. Seems like the giant fan rocket has only 1 way to fail (very kerbal).

(multiple ways for the failure to happen, to be clear, one kerbal outcome )

[sevenperforce]

36 minutes ago, tater said:

Absolutely. Seems like the giant fan rocket has only 1 way to fail (very kerbal).

(multiple ways for the failure to happen, to be clear, one kerbal outcome )

I always prefer fixed-component solutions. Like how the aerospike solves a problem that would otherwise require a moveable-geometry nozzle, simply by turning the problem inside-out.

One of the challenges for any airbreather is the mixing problem. Whether you're just using air as working mass or for a portion of combustion, you have to have a way to mix the mechanically- or shock-compressed inlet air with your fuel (or your exhaust, in a working-mass-only approach). SABRE handles the problem, of course, by actually collecting, superchilling, and injecting the air into the engine. Anything that is pass-through, though, needs a way to ensure complete mixing.

Linear aerospike engines (and some toroidal ones, though not of the annular variety) have multiple small combustion chambers which open onto the nozzle surface. I wonder if it would be possible to create an inlet between the chamber exhaust and the nozzle surface, so that the air inlet would enter perpendicular to the exhaust flow and thus mix very effectively.

[Nothalogh]

4 hours ago, sevenperforce said:

I always prefer fixed-component solutions.

Yep, Gnom did it right.

[kerbiloid]

(in Russian)

http://militaryrussia.ru/blog/topic-801.html

[sevenperforce]

The elephant in the room seems to be reuse. Even assuming all the turbomachinery and combustion chambers work as intended, all we end up with is a very mass-efficient way to get into space, but not necessarily any way to get back. His image shows a biconic entry, and he certainly has the mass budget for a little shielding, but merely claiming "biconic entry" does not mean EDL is solved. In fact, that thing looks so much like a lawn dart that I'm very puzzled to know how he imagines he'd ever be able to land it. 

If orbital EDL was this easy, then ULA and SpaceX and Roscosmos and Arianespace would already all be re-using their upper stages. Even with Starship, where you have recovery margin for days, it has been a long hard track to get to a workable design.

I would almost suggest that focusing on a Skylon-like approach is better -- build the engine as a monolithic whole and let the EDL issue be a vehicle problem. With a mass fraction (40%) fully eight times better than Skylon's (5-6%), he has all the margin in the world for a vehicle solution to EDL, but only if his engine is monolithic and can be nacelle-mounted.

[tater]

Yeah, there's definitely a moment in the presentation that reminds me of this cartoon:

I was talking on the phone with a friend about it, and it seemed to me that he needs to go back to SpaceX. Starship solves that problem (assuming they solve that problem). His vehicle is basically a starship with a different engine.

[sevenperforce]

I have connected with Bucknell on LinkedIn and necro'd an active NSF thread where he is answering some questions:

https://forum.nasaspaceflight.com/index.php?topic=43344.msg1995132#msg1995132

[Spacescifi]

On 9/19/2019 at 7:29 PM, tater said:

John Bucknell has pitched a partially air breathing NTR SSTO rocket in the past, but has now come up with an interesting chemical variant (still an SSTO, with an insanely high payload mass fraction) that has a mission averaged I_sp of 1600s (to LEO).

He's pushing it for orbital solar power construction (since the cost to orbit is low enough). Dunno, but a very interesting concept.

 

 

 

 

I too find it interesting. Somewhere I read that nuclear air breathing SSTO'S are possible, inasmuch project pluto did work.

One could even make the open cycle exhaust safe by shielding the reactor and using heat absorbed from the shield to create the heat for plasma jet thrust.

Therein lies the challenge, since shields must be great heat conductors but not melt. That is why nuclear lightbulb drives are still on the drawing board.

Even if it could solve the heat issues, it has been claimed by some that a nuclear thermal air breather craft would use up all it's uranium for nuclear reactions within days.

That is the price for high thrust nuclear craft, you run out of uranium faster. At least that is what some say.

Edited September 24, 2019 by Spacescifi

[Guest]

Actually, the problem with an NTR SSTO is that it uses uranium up too slowly. In any realistic design, you'd run out of propellant before you run out of fuel. To be economical, an NTR SSTO needs to be reusable, either on orbit or after reentry and landing. Otherwise, you'd be leaving a very expensive, and still good, nuclear reactor in orbit.

Air-breathing is an option if you can design the engine to run on either air or hydrogen. Now that I think of it, perhaps using nitrogen as propellant would help with that. Basically, you optimize your nuclear reactor as an airbreather (since air is mostly nitrogen), and in "rocket" mode, you just feed gaseous N2, evaporated by a small portion of reactor heat, into the intake, which will produce nearly the same results, as far as thermodynamics go, as feeding it cold air. 

Another option is air augmentation, as in the Gnom missile. Basically a ramjet using, instead of fuel combustion, a nuclear rocket engine. It would use more propellant, but be simpler to design.

[Spacescifi]

38 minutes ago, Dragon01 said:

Actually, the problem with an NTR SSTO is that it uses uranium up too slowly. In any realistic design, you'd run out of propellant before you run out of fuel. To be economical, an NTR SSTO needs to be reusable, either on orbit or after reentry and landing. Otherwise, you'd be leaving a very expensive, and still good, nuclear reactor in orbit.

Air-breathing is an option if you can design the engine to run on either air or hydrogen. Now that I think of it, perhaps using nitrogen as propellant would help with that. Basically, you optimize your nuclear reactor as an airbreather (since air is mostly nitrogen), and in "rocket" mode, you just feed gaseous N2, evaporated by a small portion of reactor heat, into the intake, which will produce nearly the same results, as far as thermodynamics go, as feeding it cold air. 

Another option is air augmentation, as in the Gnom missile. Basically a ramjet using, instead of fuel combustion, a nuclear rocket engine. It would use more propellant, but be simpler to design.

 

Does liquid nitrogen have the same issues of liquud hydrogen? Being hard to store because of vaping away?

If not that's great, somebody can try that one day.

Nitrogen makes a pinkish flame I read, but a blue one at peak current... whatever that means.

 

Liquid nitrogen is awesome though. Since if he can do this with hardly any preparation, then a prepped air breathing NTR with liquid nitrogen could do wonders.

 

Edited September 24, 2019 by Spacescifi
Vid

[tater]

59 minutes ago, Dragon01 said:

Actually, the problem with an NTR SSTO is that it uses uranium up too slowly. In any realistic design, you'd run out of propellant before you run out of fuel. To be economical, an NTR SSTO needs to be reusable, either on orbit or after reentry and landing. Otherwise, you'd be leaving a very expensive, and still good, nuclear reactor in orbit.

He addresses this. The nuclear version is reusable---in space. Fly it to LEO, refill it. Fly it to the lunar surface, mine water, refill with water as the vacuum propellant (or split into H and O and use the H).

59 minutes ago, Dragon01 said:

Air-breathing is an option if you can design the engine to run on either air or hydrogen. Now that I think of it, perhaps using nitrogen as propellant would help with that. Basically, you optimize your nuclear reactor as an airbreather (since air is mostly nitrogen), and in "rocket" mode, you just feed gaseous N2, evaporated by a small portion of reactor heat, into the intake, which will produce nearly the same results, as far as thermodynamics go, as feeding it cold air. 

Another option is air augmentation, as in the Gnom missile. Basically a ramjet using, instead of fuel combustion, a nuclear rocket engine. It would use more propellant, but be simpler to design.

The airbreather part just bumps the effective Isp for the launch.

[sevenperforce]

26 minutes ago, tater said:

1 hour ago, Dragon01 said:

Another option is air augmentation, as in the Gnom missile. Basically a ramjet using, instead of fuel combustion, a nuclear rocket engine. It would use more propellant, but be simpler to design.

The airbreather part just bumps the effective Isp for the launch.

The one I'm interested in is the staged-combustion version. A regular FRSC hydrolox engine is in the center, an air-augmentation (GNOM-style) duct around the engine, and the turbocharger blades spun by turbopump combustion tapoff that bleed fuel for downstream combustion.

My remarks on the necessity of the turbocharger blades:

A deeper review of the whitepaper leads me down some interesting paths. The fan blades themselves are of course critical to vertical takeoff, providing augmentation of ~320% at liftoff. Without them, static thrust would presumably be only a fraction (~26%) of GLOW, making liftoff impossible. However, they provide rapidly-dropping augmentation as increased airspeed makes their compression cycle less efficient and ram compression begins to provide more assistance. By Mach 1, augmentation drops to 220% and thrust has decreased to 76% of liftoff thrust while the vehicle's gross mass has only dropped by 2%, thus lowering T/W by 22%. By Mach 1.4, augmentation is only 180% and T/W is 32% less than at liftoff. According to the whitepaper, fan compression continues to contribute up to Mach 8 (a bold claim), but it would necessarily be only a tiny contribution. 

For as much trouble as these fan blades promise to be, I'm not certain there isn't a better alternative. Certain fanless ducted rocket designs can boost specific impulse by up to 80% with no forward airspeed. An ideal design would have an immediate increase in T/W rather than a decrease, which is critical given the gravity drag on the early stages of flight with something like Prometheus.

Edited September 24, 2019 by sevenperforce

[magnemoe]

2 hours ago, Spacescifi said:

I too find it interesting. Somewhere I read that nuclear air breathing SSTO'S are possible, inasmuch project pluto did work.

One could even make the open cycle exhaust safe by shielding the reactor and using heat absorbed from the shield to create the heat for plasma jet thrust.

Therein lies the challenge, since shields must be great heat conductors but not melt. That is why nuclear lightbulb drives are still on the drawing board.

Even if it could solve the heat issues, it has been claimed by some that a nuclear thermal air breather craft would use up all it's uranium for nuclear reactions within days.

That is the price for high thrust nuclear craft, you run out of uranium faster. At least that is what some say.

Pluto looked like it should work, or the engine looked like it should work. Rest of the system might well be harder. Navigation and heating is two major issues.
Add that surface to air missiles advanced fast, so do ICBM who was impossible to intercept and cheaper. 

Now using an NTR in an reusable rocket creates lots of problems. First is that reactor will become radioactive with use. This is not much of an issue if its single use and in deep space you can use shadow shields and always be nose first then docking to an station or other ships. 
on ground this will be much more of an issue. 
Second is that an crash will be an nuclear spill event. Also not sure how fast throttle an NTR is. 
An air breathing NTR will have the risk of oxygen and nitrogen become radioactive because of neutron radiation and you will have 2000 centigrade oxygen around inside the reactor. 

I'm pro nuclear as in we should build lots of nuclear plants. 
Landing an NTR back on Earth: just no.  

[Spacescifi]

12 minutes ago, magnemoe said:

Pluto looked like it should work, or the engine looked like it should work. Rest of the system might well be harder. Navigation and heating is two major issues.
Add that surface to air missiles advanced fast, so do ICBM who was impossible to intercept and cheaper. 

Now using an NTR in an reusable rocket creates lots of problems. First is that reactor will become radioactive with use. This is not much of an issue if its single use and in deep space you can use shadow shields and always be nose first then docking to an station or other ships. 
on ground this will be much more of an issue. 
Second is that an crash will be an nuclear spill event. Also not sure how fast throttle an NTR is. 
An air breathing NTR will have the risk of oxygen and nitrogen become radioactive because of neutron radiation and you will have 2000 centigrade oxygen around inside the reactor. 

I'm pro nuclear as in we should build lots of nuclear plants. 
Landing an NTR back on Earth: just no.  

 

Nuclear lightbulb drive rocket's do not have radioactive exhaust I read.

Are you saying that as long as that reactor is running it will emit neutron radiation in all directions whether rocket is expelling exhaust or not?

And the neutron radiation will go right through the hull into the outside environment... barring making the enitre hull neutron absorbent? Which may be impractical except with project Orion.

Edited September 24, 2019 by Spacescifi

[Guest]

32 minutes ago, Spacescifi said:

And the neutron radiation will go right through the hull into the outside environment... barring making the enitre hull neutron absorbent? Which may be impractical except with project Orion.

Actually, it's not that hard. Lithium-6 is a very good neutron absorbent, with Boron-10 being up there, too. Both of those are very lightweight, and in fact has been proposed as radiation protection for spaceships (they're good against cosmic ray neutrons, too).

21 minutes ago, magnemoe said:

Now using an NTR in an reusable rocket creates lots of problems. First is that reactor will become radioactive with use. This is not much of an issue if its single use and in deep space you can use shadow shields and always be nose first then docking to an station or other ships. 
on ground this will be much more of an issue. 
Second is that an crash will be an nuclear spill event. Also not sure how fast throttle an NTR is. 
An air breathing NTR will have the risk of oxygen and nitrogen become radioactive because of neutron radiation and you will have 2000 centigrade oxygen around inside the reactor. 

Nitrogen-15 is stable, so there's no risk here. Oxygen-17 likewise. If you hit either Nitrogen-14 or Oxygen-16 with a neutron, you'll get another stable isotope. So the air won't become radioactive. As long as you're not throwing out pieces of the core with the exhaust, you'll be fine. 

Radioactivity on the ground will be an issue only in case of a crash. If a reactor is shut down, it doesn't emit a lot of radiation. NTR, after landing, would need to be handled with robotic vehicles, but that's the best way to handle normal rockets, as well. As for neutron activation of the components, I think it can be dealt with, for instance, by making as much as possible (except the shielding) from carbon composites. They don't undergo neutron activation.

NERVA was subjected to worst-case destructive testing towards the end (i.e. they blew it up). It seems like it survived that, so as long as reactor containment stays intact, there will be no spill. And even if there was, we're talking an event the size of the recent Russian spill, not Chernobyl. Just treat them like you would a hydrazine rocket (not like the Chinese treat them, though...). 

[Spacescifi]

1 hour ago, Dragon01 said:

Actually, it's not that hard. Lithium-6 is a very good neutron absorbent, with Boron-10 being up there, too. Both of those are very lightweight, and in fact has been proposed as radiation protection for spaceships (they're good against cosmic ray neutrons, too).

Nitrogen-15 is stable, so there's no risk here. Oxygen-17 likewise. If you hit either Nitrogen-14 or Oxygen-16 with a neutron, you'll get another stable isotope. So the air won't become radioactive. As long as you're not throwing out pieces of the core with the exhaust, you'll be fine. 

Radioactivity on the ground will be an issue only in case of a crash. If a reactor is shut down, it doesn't emit a lot of radiation. NTR, after landing, would need to be handled with robotic vehicles, but that's the best way to handle normal rockets, as well. As for neutron activation of the components, I think it can be dealt with, for instance, by making as much as possible (except the shielding) from carbon composites. They don't undergo neutron activation.

NERVA was subjected to worst-case destructive testing towards the end (i.e. they blew it up). It seems like it survived that, so as long as reactor containment stays intact, there will be no spill. And even if there was, we're talking an event the size of the recent Russian spill, not Chernobyl. Just treat them like you would a hydrazine rocket (not like the Chinese treat them, though...). 

 

That is why I like the idea, as they are perfect for scifi.

All you really need is unusually heat resistant materials that we do not currently have.

With those, you could fly a gas core NTR up to orbit and back. Since thrust per amount of propellant burned is higher the hotter it is.

In real life, thrust would be lower due to not having such heat resistant material available that would dramatically allow higher thermal energies in rocket thrust.

 

Fusion is a dead end right now in my opinion.

NTR is much more scifi and easier to achieve too in scifi. No fussing about with magnetic fields, just make a scifi heat resistant material.

In real life it is easier than fusion but lower thrust unless augmented with air or certain propellants/mixes.

Edited September 24, 2019 by Spacescifi

[Guest]

15 minutes ago, Spacescifi said:

With those, you could fly a gas core NTR up to orbit and back. Since thrust per amount of propellant burned is higher the hotter it is.

In real life, thrust would be lower due to not having such heat resistant material available that would dramatically allow higher thermal energies in rocket thrust.

Quarz glass. It's what you use to make a nuclear lightbulb. You don't need magic materials, performance is more than enough for surface to orbit. You just need good engineering, a lot of money, and someone with enough guts to make it happen. Some Soviet engineers were actually trying to do just that, and if they didn't have to go make Buran instead, who knows what they'd have ended up with...

Fusion is not a dead end, but it will take far more time to become affordable, and therefore suited for more far-out SF. It doesn't require any magic, either, you can do a lot with magnetic fields. One nice thing about them is that they don't melt, so you can get very hot with that.

[Spacescifi]

20 minutes ago, Dragon01 said:

Quarz glass. It's what you use to make a nuclear lightbulb. You don't need magic materials, performance is more than enough for surface to orbit. You just need good engineering, a lot of money, and someone with enough guts to make it happen. Some Soviet engineers were actually trying to do just that, and if they didn't have to go make Buran instead, who knows what they'd have ended up with...

Fusion is not a dead end, but it will take far more time to become affordable, and therefore suited for more far-out SF. It doesn't require any magic, either, you can do a lot with magnetic fields. One nice thing about them is that they don't melt, so you can get very hot with that.

Quartz may work, but I do not see it being able to survive the thermal energy needed to lift 500 ton SSTO'S (average jet liner weight). I am thinking it would have to be lightweight solution at best. Orion pusher plate thrust it is not.

Only with scifi heat resistant materials could a gas core ever lift something like this with 40 crew and cargo to orbit:

As for fusion:

Sure magnetic fields don't melt, but they also leak plasma. Which prevents a sustained fusion reaction from taking place.

Causing fusion is not too difficult, sustaining it using magnetic fields so far has proven ineffective due to plasma leakage which leads to a drop in temperature, which leads to the fusion process stopping.

Edited September 24, 2019 by Spacescifi