Rotating Detonation Engines

Another reason to use N6 is for it to be a chemical version of an NSWR.

It may lend itself to detonation engines—plus, the nitrogen gas can be used to fill lava tubes.
This way, astronauts only need their own oxygen for breathing. Pure nitrogen filled tubes knock a leg out of the fire triangle.

It is thus an explosion hazard—but less a fire hazard.

Perhaps an ozone tank to have nitric acid come out hot with kerosene afterburners—a very long engine with all reactions taking place at speed?
 
publiusr said:
Some at NSF think hexanitrogen might be best suited for detonation engines:

Now consider temperature. We get 185.2kcal/mol out of N2, and it's pretty complicated to figure out what the resulting temperature is, involving the Shomate equation to figure out what temperature it's gonna get to from a 70K start.

The answer, I think, maybe, is about 2300K, which is terrible. But someone else needs to do this, I don't get the math so I'm not going to try and publish that, it's an AI educated guess, worth whatever you think that is.

That's going to result in lowering of the Isp by another factor of sqrt(3600/2300) to about 265. Useless.

So running N6 through a standard De Laval nozzle system isn't going to be very useful.

Perhaps a detonation system would be better. Far beyond my skills to calculate.

Hexanitrogen propellant

Hexanitrogen propellant
forum.nasaspaceflight.com forum.nasaspaceflight.com

Hypergolics are in that range so perhaps not so useless. Just having one tank (perhaps self-pressurizing) and a simpler engine set up is worth the price of admission.
Click to expand...

Before everyone gets too enthusiastic about hexanitrogen, HERE'S a post about it by Derek Lowe (and from there you can get to the original nature paper), and the bad news is that Hexanitrogen is only stable for long periods at cryogenic temperatures. At 298K (24 degrees Celsius) it's half-life is 35.7 milliseconds . . .

cheers,
Robin.
 
robunos said:
Before everyone gets too enthusiastic about hexanitrogen, HERE'S a post about it by Derek Lowe (and from there you can get to the original nature paper), and the bad news is that Hexanitrogen is only stable for long periods at cryogenic temperatures. At 298K (24 degrees Celsius) it's half-life is 35.7 milliseconds . . .

cheers,
Robin.
Click to expand...
“Plenty of other hypothetical polynitrogen species turn out to have basically no barrier at all by comparison, which is why they’re still hypothetical, and you will be too if you try to make them on any kind of scale.”

Outstanding.
 
dannydale said:
Now I'm wondering if brisance can be a parameter to be played with for an RDE. More shatteringly boomful is more thrust and way more material fatigue versus less, mayhaps?
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Brisance is absolutely a big concern for RDREs as direct injection of liquid propellants creates higher detonation pressures than gaseous injection. You're right that more boom gives more thrust, and we saw a little hurt in heat sink combustors but when NASA started actively cooling liquid RDREs they started seeing absolutely brutal fatigue failures. Big problem that needs to be solved if we want to actually harness those condensed phase detonation pressure ratios
 
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TripleRedundantSlimeBall said:
Brisance is absolutely a big concern for RDREs as direct injection of liquid propellants creates higher detonation pressures than gaseous injection. You're right that more boom gives more thrust, and we saw a little hurt in heat sink combustors but when NASA started actively cooling liquid RDREs they started seeing absolutely brutal fatigue failures. Big problem that needs to be solved if we want to actually harness those condensed phase detonation pressure ratios
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I guess if there is a fatique problem, it has more to do with the rotating bending force. The pressure is a design choice
 
For detonation engines, subtractive manufacturing might be best.

I would not won’t want 3D print engines for that—unless things keep improving.
 
publiusr said:
For detonation engines, subtractive manufacturing might be best.

I would not won’t want 3D print engines for that—unless things keep improving.
Click to expand...
I mean, ~25,000psi has been demonstrated for 3d printing before, in laser-sintered stainless steel.

A 3d printed 1911.
 
Hic Rhodus, Hic Salta. I. E. PROVE IT AT TRL 9. (and I really, genuinely, sincerely hope you will be able to do so.)
 
martinbayer said:
Hic Rhodus, Hic Salta. I. E. PROVE IT AT TRL 9. (and I really, genuinely, sincerely hope you will be able to do so.)
Click to expand...
The pistol?
View: https://www.youtube.com/watch?v=lwbNOo2aBGA


It had typical newly-made 1911 issues, which are caused by the nature of the beast: hand-fitting parts. Extractor and ejector need a little tuning, and the feed ramp on the barrel needs polishing to a full mirror finish.

The only reason it's not sitting on some dude's belt is because he prefers other weapons than old slabsides. 3lbs of lead and steel is not comfortable to carry without good gear.
 
Disclaimer: I had repeated fires and several 'Unplanned Disassembly' events refluxing Lithium Aluminium Hydride during my Uni course. I became very proficient with a CO2 extinguisher...

Um, perhaps problem with current RDE designs is having one (1) travelling flash ?

By analogy with magnetron, stabilised by 'strapping' cavity pairs to work in unison...
 
Nik said:
Disclaimer: I had repeated fires and several 'Unplanned Disassembly' events refluxing Lithium Aluminium Hydride during my Uni course. I became very proficient with a CO2 extinguisher...

Um, perhaps problem with current RDE designs is having one (1) travelling flash ?

By analogy with magnetron, stabilised by 'strapping' cavity pairs to work in unison...
Click to expand...
You know, you're likely right.
 
publiusr said:
For detonation engines, subtractive manufacturing might be best.

I would not won’t want 3D print engines for that—unless things keep improving.
Click to expand...
absolutely; but the 3d printing hype train is already in motion, no stopping it now

Scott Kenny said:
I mean, ~25,000psi has been demonstrated for 3d printing before, in laser-sintered stainless steel.

A 3d printed 1911.
Click to expand...
printed parts have already exceeded 100KSI yield with good heat treats (https://www.protolabs.com/media/1022811/inconel-718-042921.pdf). The problem is not with raw loading but rather repeated loading: because prints are made of sintered particles, they have a microstructure that's filled with porosity and cracks. Hot Isostatic Pressing will substantially reduce this porosity, but the remaining microcracks and rough surface finish will nucleate fatigue cracking, which is substantially accelerated by getting blasted with a detonation wave thousands of times a second

martinbayer said:
Hic Rhodus, Hic Salta. I. E. PROVE IT AT TRL 9. (and I really, genuinely, sincerely hope you will be able to do so.)
Click to expand...
3D printed gun parts (suppressors) are already available for public consumption for the record (https://huxwrx.com/); not quite load bearing the same way as bolt heads and chambers, but still hard wear parts. printing is just straight up a bad manufacture process for the block and cylinder shapes we currently use for breech locking mechanisms

Nik said:
Disclaimer: I had repeated fires and several 'Unplanned Disassembly' events refluxing Lithium Aluminium Hydride during my Uni course. I became very proficient with a CO2 extinguisher...

Um, perhaps problem with current RDE designs is having one (1) travelling flash ?

By analogy with magnetron, stabilised by 'strapping' cavity pairs to work in unison...
Click to expand...
correct, single wave modes have been destroying chambers at NASA Marshall; two corotating waves tend to be easier on the stand. Problem is that the community doesn't have a great idea at how to design to that criterion; we sort of just run combustors and see how they react to certain parameters and inputs
 
I cannot thank you enough for that reveal.

Proof once again that MSFC is still relevant in the 21st century. If only I could get NewSpacers to acknowledge that.

I seem to remember someone at Starship Modeler comparing both plastic models of SLS--saying that one provider had one piece engines due to slide molding.

Could that be scaled up? Maybe 3D prints used as a mold themselves somehow? Dissolve a crumbly 3D print to release a casting perhaps.

RS-68 engines are simpler than RS-25s--3D print good enough for that..to allow cheaper hydrogen rocketry?
 
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publiusr said:
I cannot thank you enough for that reveal.

Proof once again that MSFC is still relevant in the 21st century. If only I could get NewSpacers to acknowledge that.

I seem to remember someone at Starship Modeler comparing both plastic models of SLS--saying that one provider had one piece engines due to slide molding.

Could that be scaled up? Maybe 3D prints used as a mold themselves somehow? Dissolve a crumbly 3D print to release a casting perhaps.

RS-68 engines are simpler than RS-25s--3D print good enough for that..to allow cheaper hydrogen rocketry?
Click to expand...
Printed molds for casting are very much a thing, but I don't know if it makes sense for this kind of aerospace application.

RS-68 is an interesting reference, because it was so much cheaper than SSME Griffin and others at NASA really wanted to use it on a human-rated vehicle. But the ablative nozzle was one of the huge sticking points, that and the hydrogen fireball at ignition. Add an SSME-style hand-buikt regeneratively cooled nozzle onto RS-68, suddenly it's not nearly as cheap. Today, you could (in theory) design an additive-manufactured channel wall nozzle which wouldn't be AS cheap as the ablative nozzle but still be enormously less expensive than an SSME. They may be able to do this for future RS-25 production to bring motor costs down steeply, but it takes money to get there and SLS money is in the danger zone.
 
Channel wall would indeed seem better than RS-25's layout.Anyone look at partitions between RS-68...spreading them out on Ares V?

F-1s peeked out a bit requiring shroud/fin on the periphery. Saturn V-B was to have a single sustainer like Atlas.

Maybe a single RS-68 as an air-start sustainer with RS-25s or something recovered like Vulcan's proposed engine unit.

An RS-68 at altitude might be less of a problem with respect to self-immolation.
 
At least for typical Nickel alloys, 3d printing gives much better mechanical properties than casting. Nickel alloys tend to have an uniform compostite distribution when beeing casted and of course, porosity occurs also in casrings. Additionally, printing gives much more freedom in design which enables much better cooling.
 
Nicknick said:
At least for typical Nickel alloys, 3d printing gives much better mechanical properties than casting. Nickel alloys tend to have an uniform compostite distribution when beeing casted and of course, porosity occurs also in casrings. Additionally, printing gives much more freedom in design which enables much better cooling.
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Where does machining rank in this process spectrum?
 
martinbayer said:
Where does machining rank in this process spectrum?
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Mashining is awfull, I remember a crazy research project with an experimental heat exchanger. The heat exchager was made out of plates (Nickel alloy, forgott which one) with many drilled holes. About 10 % of the holes were blocked by broken drills, despite an ultra slow drilling process with cooled drills in an horizontal position.

I doubt that there is even large billet material available, but I might be wrong.

Btw Counter rotatung doesnt make sense, two flame fronts wuth 180 deg offset would eliminate the bending forces.
 
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"We flew the first ever high-thrust RDRE," Duggleby said. "I don't know that there's an actual comparison right now."
(Venus Aerospace)

2y3U6sW7YG82oerAdcSFK9-970-80.jpg.webp

Indeed, and beautifully.

cdn.jwplayer.com

Venus Aerospace completes first US flight test of Rotating Detonation Rocket Engine

Venus Aerospace completed a flight test of a Rotating Detonation Rocket Engine (RDRE) on May 14, 2025. The engine is designed to "enable vehicles to travel 4 to 6 times the speed of sound from a...
cdn.jwplayer.com

CgAmNA98oZnJGgxCfGSqD9-970-80.jpg.webp


www.space.com

'A game changer': Space shuttle astronaut Pam Melroy joins Venus Aerospace after revolutionary rocket engine breakthrough

"We believe in a future where this is the engine powering everything..."
www.space.com www.space.com
 
Venus Aerospace: "We flew the first ever high-thrust RDRE," Duggleby said. "I don't know that there's an actual comparison right now."

It is not a rocket engine but merely a ramjet, so not an RDRE but merely an RDE.

And what do they mean by "high-thrust"?
How much thrust did that engine in the video actually produce?
 
Dagger said:
Venus Aerospace: "We flew the first ever high-thrust RDRE," Duggleby said. "I don't know that there's an actual comparison right now."

It is not a rocket engine but merely a ramjet, so not an RDRE but merely an RDE.

And what do they mean by "high-thrust"?
How much thrust did that engine in the video actually produce?
Click to expand...
Its a bigger archievment in my view, a kind of air breathing propulsion system which might also work in rocked mode. Since it can vertically start from ground, it surly does't rely on ram.
 
@Dagger : You are absolutely right with your skepticism. However, if we understand that the video was not tempered, the launch acceleration is noteworthy of something of power, even for a test vehicle reduced to an empty pipe with a single gallon of fuel (it seems we see a flameout right at the end?). The point that the ramp is not vertical could indicate a total thrust lacking somewhat but I think it´s more a factor of safety with the launch trajectory and point of impact.

And, let´s remind all, even hopping across a puddle is... (usually) suborbital.
 
"...prints are made of sintered particles, they have a microstructure that's filled with porosity and cracks."
Perhaps not relevant, but I remember seeing a system for 'wicking' a sinter with another metal or alloy.

Sorry, cannot find reference, but process was sorta-kin to trad 'Lost Wax' method, just with porous void...
The result was intended for decorative purposes, but apparently looked and, yes, sounded like a monolithic casting.
 
Nik said:
"...prints are made of sintered particles, they have a microstructure that's filled with porosity and cracks."
Perhaps not relevant, but I remember seeing a system for 'wicking' a sinter with another metal or alloy.

Sorry, cannot find reference, but process was sorta-kin to trad 'Lost Wax' method, just with porous void...
The result was intended for decorative purposes, but apparently looked and, yes, sounded like a monolithic casting.
Click to expand...
With investment casting, you will have troubles to clean the cooling borers from the ceramic shell. I don't know if it helps against the unwanted unmixing of the alloy.

One reason why it is so difficult to machine is the varying degree of hardness due to the varying material composition.

So far, 3d printing works well on rocket engines and Space X is using it as well to a large degree in their newest designs. I believe, this is the way to go, if there will be troubles related to printing, its much more likely that improving the printing technology will be the better solution than switching to castings.
 
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TripleRedundantSlimeBall said:
printed parts have already exceeded 100KSI yield with good heat treats (https://www.protolabs.com/media/1022811/inconel-718-042921.pdf).
Click to expand...
Very cool! I hadn't seen that, but I did know about the pistol.



TripleRedundantSlimeBall said:
The problem is not with raw loading but rather repeated loading: because prints are made of sintered particles, they have a microstructure that's filled with porosity and cracks. Hot Isostatic Pressing will substantially reduce this porosity, but the remaining microcracks and rough surface finish will nucleate fatigue cracking, which is substantially accelerated by getting blasted with a detonation wave thousands of times a second
Click to expand...
I'm not sure how much post-printing polishing etc needed to happen for the pistol, but at the very least I know there were multiple different heat treatments involved. Stainless Steel will gall if each piece is the same hardness, but if one is harder than the other they'll slide just fine long-term.



TripleRedundantSlimeBall said:
3D printed gun parts (suppressors) are already available for public consumption for the record (https://huxwrx.com/); not quite load bearing the same way as bolt heads and chambers, but still hard wear parts. printing is just straight up a bad manufacture process for the block and cylinder shapes we currently use for breech locking mechanisms
Click to expand...
Bad design for operating pressure versions. I've seen a lot of work done with plastic parts in the general shapes and manually cycled just to prove it will function.



TripleRedundantSlimeBall said:
correct, single wave modes have been destroying chambers at NASA Marshall; two corotating waves tend to be easier on the stand. Problem is that the community doesn't have a great idea at how to design to that criterion; we sort of just run combustors and see how they react to certain parameters and inputs
Click to expand...
What that says to me is, whatever length of channel the detonation wave travels through and has enough time to refill before it booms again, your test RDE needs to be 2x that length and have 2 starts in it 180deg apart on the circle.
 
Nicknick said:
Its a bigger archievment in my view, a kind of air breathing propulsion system which might also work in rocked mode. Since it can vertically start from ground, it surly does't rely on ram.
Click to expand...

TomcatViP said:
@Dagger : You are absolutely right with your skepticism. However, if we understand that the video was not tempered, the launch acceleration is noteworthy of something of power, even for a test vehicle reduced to an empty pipe with a single gallon of fuel (it seems we see a flameout right at the end?). The point that the ramp is not vertical could indicate a total thrust lacking somewhat but I think it´s more a factor of safety with the launch trajectory and point of impact.

And, let´s remind all, even hopping across a puddle is... (usually) suborbital.
Click to expand...

Venus Aerospace works on a Ramjet engine that they call the "Venus Detonation Ramjet (VDR)".
It has an RD engine in the back of the cone, to get things started, and at Mach 1+ the ram burner is also lit to increase thrust further. As speed increases the RD engine is throttled down until at Mach 3.5 only the ram burner is in operation:

View: https://www.youtube.com/watch?v=FW1RQBdu35A&t=1098s
 
Nice one! Thank you @Dagger.

Notice the high pressure collect downstream of the RDE/Inlet cone, compressed/mixed and routed peripherally around the nozzle as what appears a fluidic TVC(?).
 
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TomcatViP said:
Nice one! Thank you @Dagger.

Notice the high pressure collect downstream of the RDE/Inlet cone, compressed/mixed and routed peripherally around the nozzle as what appears a fluidic TVC(?).
Click to expand...
I see what you mean, however it is not clearly shown in the image you posted Wednesday,
or in the images on their website https://www.venusaero.com/

That website is surprisingly lean, considering they exist already several years.
 
@Dagger : A screenshot of the video you posted earlier:

Screenshot 2025-09-18 151816.png

Notice from Right to Left
- the notch surrounding the nozzle
- the temp gradient and compression imparted to the flow in the notch from low Mach to supersonic (Conv-Div)
- the external plumbing all around the nozzle area pointing to the notch base that constitute a discretized injection surface surrounding the nozzle
- the cylindrical elements (left side) at the source of the plumbing encased in the engine core structure
- the notches leading to these cylinders
- the shape of those notches with a compressive action from downstream of the RDE nozzle (supersonic flow)

Notice also that the section cut exclude those cylindrical elements to not expose more their precise function.

Hope it helps.
 
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