6 ms·
In the US, a rotating detonation rocket engine takes flight
- ColinWright 1y agoFrom the article: "In contrast to a traditional rocket engine, in which a highly pressurized propellant and an oxidizer are injected into a combustion chamber where they burn and produce an energetic exhaust plume, a rotating detonation engine is different in that a wave of detonation travels around a circular channel. This is sustained by the injection of fuel and oxidizer and produces a shockwave that travels outward at supersonic speed." Nope ... on my way to do web searches to try to figure out what this means. First stop: https://en.wikipedia.org/wiki/Rotating_detonation_engine https://en.wikipedia.org/wiki/Rotating_detonation_engine "A rotating detonation engine (RDE) uses a form of pressure gain combustion, where one or more detonations continuously travel around an annular channel. ... In detonative combustion, the flame front expands at supersonic speed. It is theoretically up to 25% more efficient than conventional deflagrative combustion ... Disadvantages include instability and noise." No images, no animations. OK ... bookmarked, and I'll chase the references later. Edit: OK, here's the best reference I've found so far: https://www.sandboxx.us/news/what-is-a-rotating-detonation-engine-and-what-could-it-mean-for-aviation/ https://www.sandboxx.us/news/what-is-a-rotating-detonation-e... Now back to work.
- philipodonnell 1y agoIf I’m understanding this correctly, if you set off one bomb the explosion travels at a certain speed, but if you put a bunch of bombs in a circle and set them off one at a time, the very last explosion will be going a lot faster than the first one?
- kd5bjo 1y agoFrom my understanding, it's more that the explosion phase of a detonation is more fuel-efficient than the burning phase, but can't last very long under normal circumstances because the flame front is moving so fast-- This is a trick to continue fueling the explosion to sustain it over an indefinite time period. Think about it in terms of an old-fashioned gunpowder line fuse: If you lay it out in a ring and have some kind of mechanism to continuously place down new gunpowder on the ring in front of the flame, you can keep it going until you run out of fuel.
- twic 1y agoWhat i've never understood is how detonation can be more efficient than deflagration. What does that mean? Both types of engine take a mix of fuel and oxidiser and turn it into hot combustion products. The hot combustion products then expand through a nozzle to produce thrust. How is that process different between the two? Does a deflagration engine leave some fuel unburnt, that a detonation engine burns? Does the combustion of the same fuel somehow produce more heat? Or less heat but more pressure? Is it something about the expansion? To put it another way, if you set up a deflagration engine and a detonation engine next to each other, and fed them fuel and oxidiser at the same rate, how would the streams of exhaust gas coming out of them look different? What other external differences would you see?
- Symmetry 1y agoThe energy produced by the combustion is the same but different fractions of it are converted into work. Just like efficiency differences in other types of heat engine.
- slow_typist 1y agoη = 1 - ( T_c / T_h ) Carnot-Efficiency is the theoretical limit of the cycle’s ability to get work out of the thermal energy where T_c is the exhaust (coldest) temperature after expansion and T_h the hottest temperature (before expansion). Temperatures given in K (Kelvin), so 100% if you manage to get T_c to absolute zero temperature.
- mannykannot 1y agoThis is mentioned in the introduction here [1]. The version I'm looking at is an image, so I cannot easily copy-paste the relevant passage, but it seems to say that the efficiency gain comes from detonation causing the combustion to occur at a higher pressure than in the case of deflagration. Generally speaking, higher peak pressures increase the efficiency of heat engines, as this allows for greater expansion of the working fluid, and thus more work being done for the same fuel consumption. With regard to your comparison, I guess this means that the detonation engine can have a higher pressure in the combustion chamber, together with a larger bell, a faster-moving exhaust, or some combination. [1] https://arc.aiaa.org/doi/10.2514/6.2013-3971 https://arc.aiaa.org/doi/10.2514/6.2013-3971
- Symmetry 1y agoYou've got the speed at which a detonation progresses within the explosive material and the speed at which the shock wave travels through the air. Neither is going to change based on the bomb's arrangement. But if you detonate a string of bombs so that each goes as the shock front from the first reaches it you can get, through constructive and destructive interference, a shockwave going mostly in one direction. But that's mostly not related to how this engine works.
- magicalhippo 1y agoIntegza made a YouTube video[1] where he visited a lab where they had a RDE, and includes some nice explanations, animations and slow-mos of the prototype in action. His channel has a certain flavor, but at least the video is informative. [1]: https://www.youtube.com/watch?v=fRMMSyCcTDI https://www.youtube.com/watch?v=fRMMSyCcTDI
- zelos 1y agoScott Manley has a great video about them: https://www.youtube.com/watch?v=rG_Eh0J_4_s https://www.youtube.com/watch?v=rG_Eh0J_4_s
- coreyh14444 1y agoMy first thought when I read this: "I bet Scott Manley has a video about this."
- deleted 1y ago[deleted]
- pxndxx 1y agoSteve Mould has a "rotating flame" video which also helps visualize this: https://www.youtube.com/watch?v=SqhXQUzVMlQ https://www.youtube.com/watch?v=SqhXQUzVMlQ
- Symmetry 1y agoThose descriptions are actually both correct, but one is describing the elephant's trunk and another the elephant's ear.
- Symmetry 1y agoTo be a bit more clear, the detonation is racing around a circular track in one plane, but the net thrust is in the direction perpendicular to that plane. Fuel and oxidiser are continuously pumped in all along the track, dropping to ~0 after a detonation and rising afterwards until the detonation front arrives again. Since you don't have to pump into a continual high pressure deflagration like in a conventional rocket engine this looks like it should be easier in terms of pump power. Rocket engine efficiency, like all heat engine efficiency[1], governed by the difference in temperature between hot and cold in the cycle. Because at any given point in a detonation engine the combustion engine only comes in pulses it can reach temperatures that would otherwise melt the rocket engine. That's true of regular rocket engines too, which use active cooling, but seems more true of a detonation engine. And I would guess that the exhaust, already being supersonic, needs less of a chock on the de Laval nozzle to ensure laminar flow. [1] Strictly speaking this only applies to combustion rocket engines. An ion engine, for instance, is a rocket engine but not a heat engine.
- kragen 1y agoBy "chock" do you mean "impact"? In English a chock is a rubber wedge you put under a wheel to keep it from rolling, or various similar objects, or the act of using one to keep something from moving: https://en.wiktionary.org/wiki/chock https://en.wiktionary.org/wiki/chock
- Symmetry 1y agoOops, that should have been "choke".
- yread 1y agoThe first reference in the wiki article has a nice animation https://www.rtx.com/news/2025/03/04/more-power-no-moving-parts-rotating-detonation-engine https://www.rtx.com/news/2025/03/04/more-power-no-moving-par...
- hammock 1y agoI imagine an internal combustion engine with a ring of spark plugs firing rapidly in sequence into a nozzle that has fuel/air injected uniformly That is my naive attempt to grok with an analogue, that is probably wrong.
- xeonmc 1y agoBasically it's a turbine engine but the rotating blades are replaced with orbiting shockwaves instead.
- kragen 1y agoThat makes no sense at all. How do you think a turbine engine works?
- idiotsecant 1y agoThis is a very low-information post. It would be more useful if you elaborate civilly on why you disagree with parent post.
- Izikiel43 1y ago> Turbine made out of shockwaves That sounds like something out of sci-fi, amazing.
- jasrys 1y agoNASA tested one at Marshall about a year ago: https://www.youtube.com/watch?v=UShD03eG9IU https://www.youtube.com/watch?v=UShD03eG9IU
- whatevaa 1y agohttps://youtu.be/RVxgyz_avQM?si=S2gqMXGJfx0tkC7h https://youtu.be/RVxgyz_avQM?si=S2gqMXGJfx0tkC7h
- numpad0 1y agoThe most fundamental idea of a detonation engine is that, if you substitute fuel "burning" process with subsonic propagation used in every conventional engines with fuel "explosion" process with supersonic wavefront, the reactions will become more instantaneous and energetic and that improves efficiency. This is the detonation part of detonation engine concept. The rotating part is a solution to the problem that forcing a continuous sustained explosion inside an engine can be complicated. By letting the explosion constantly happening, expanding, and traveling radially across a thin cylindrical gap, it solves such problems as sustained combus-^H^H^H detonation, fuel supply, etc. It's not the only possible type of an engine based on detonation principle, but so far the most promising. Detonating piston engines for cars, for example, are much less promising. Engine part is just regular reaction rocket. It shoots the gas out the back. The faster and heavier the gas, the more reaction force it creates. This isn't the first RDE ever to have been built, fired, or fired in a freefall, but it's finicky and experimental enough that it warrants a news story like this.
- zck 1y ago>...if you substitute fuel "burning" process with subsonic propagation used in every conventional engines with fuel "explosion" process with supersonic wavefront... This fragment confused me, because it looks like there are three substitutions. There aren't; there's only one. Read it as: If you substitute fuel burning (which has subsonic propagation, and is used in every conventional engine) with fuel explosion (which has a supersonic wavefront)... The first and third "with" link a noun (the respective process) with a property (how fast it shoots gas out the back). The second "with" is the substitution. English is hard! I'm a native speaker, and I had to take a look at a few webpages to understand just this part! And I'm still left with questions, like why subsonic is described as having "propagation", but supersonic is described as having a "wavefront". Is this a distinction with a difference? I don't know.
- numpad0 1y agoI must admit that I'm in fact not a native English speaker and my sentence construction is still jarring at times... sorry for that. That distinction was not intentional, but IIUC, chemical reactions propagating faster than the speed of sound(of surrounding material, not necessarily of air(which idk how is it even defined, ductile limit or something(of air!?))) has effect of consolidating what would normally be multiple consecutive waves of density changes following one another, into a single shockwave with higher peak pressure, and higher peak pressure in an engine is generally thought to lead to higher exhaust gas velocities and better efficiencies so long that the engine holds. I think this is what some comments mentioning P-V diagrams and Carnot efficiency is meaning to say, except mine is in uneducated terms.
- foobarbecue 1y agoYeah, that bit about the shockwave in the first quote is a weird thing to say; I suspect LLM use here. All shockwaves "travel outward at supersonic speed."
- casey2 1y ago2 hours? What's the point? It could be 0 minutes with a 0% explosion rate and the total travel time would probably be longer.
- zdragnar 1y agoThe point is reduced fuel use and faster response times (either emergencies or warfare). Maintaining a detonation (as opposed to deflagration) is quite a technical challenge. If nothing else, it pushes mechanical engineering and material science forward.
- K0balt 1y agoAt supersonic speeds, the efficiency of an engine like this can be very high, and at high altitudes, travel is very efficient. People don’t seem to get that there is potential for more efficient transport at supersonic speeds/ hypersonic speeds. The ultimate example of this a satellite. How many times does it circle the world every 45 min, all on that initial fuel it took to get it up there? It seems wasteful, but it’s actually the most efficient form of transportation in existence. Of course, hypersonic transport would not be as efficient as a satellite, but still, at 100k feet, for example, you can go 5000km/h while only consuming the same amount of fuel that you would use to go 300km/h at sea level. The potential for efficiency gains are huge, and the fuel cost of getting to altitude is mostly returned in the descent. Of course, the technical challenges are also huge, so I don’t expect to see hypersonic airliners any time soon, but when we do get them, they could easily be 6-7x as efficient as existing transports. And it would be nice to have long haul flights be 3x as fast or faster. People mistakenly assume that this kind of travel only has applications for the military or the elites, and, like air travel in general, that will probably be initially true. But after the rich and the government foots the bill in lives and research to make it safe and economical, it should hold huge gains for society at large. Science and engineering is one of the only cases where trickle down economics actually kind of works. In knowledge, a rising tide really does lift all boats.
- hermitcrab 1y agoPresumably, you have to be travelling quite a distance before hypersonic/high-altitude flight becomes more efficient than current commercial airliners.
- verzali 1y ago>Sassie Duggleby and her husband, Andrew Duggleby, founded Venus Aerospace nearly five years ago with the long-term goal of developing powerful rotating detonation engines and building a hypersonic aircraft that could carry perhaps a dozen passengers and travel at astonishingly fast speeds worldwide. As an engineering project it sounds really cool, but is the application really commercial travel? I would have thought the military would be far more interested and much better funded.
- jcims 1y agoFrom the bottom of the article: "We're actively engaged with US defense and national security agencies as well as commercial partners exploring hypersonic applications in logistics, aerospace, and future mobility—including large primes," she said. "The enthusiasm we’re seeing reflects a broad recognition that Venus’s technology can unlock new operational and economic possibilities across multiple markets."
- jrmg 1y agoWhat are ‘large primes’ here?
- cookingmyserver 1y agoPrimary defense contractors. Lockheed, Boeing, Raytheon, etc.
- twothreeone 1y agoM136,279,841 is pretty big..
- deelowe 1y agoIt's a smokescreen for hypersonic missile development. It's a common tactic. I knew someone who worked on a novel satellite surveillance system. Their pitch was that it would allow them to engage in futures trading because the resolution of their satellites would allow unique insights into global trade for certain markets using realtime optical imaging. The guy was former Lockheed. One night at dinner I told him to cut the BS and that their real goal was to target military/government contracts. He said "off the record" this is correct. This an unspoken goal by everyone involved - management, investors, etc. My understanding is it can be hard to position yourself as a defense company as a start up if you don't already have a foothold in the space.
- aaron695 1y agoPress release videos - https://drive.google.com/drive/folders/194_lxE-vy_ha7-5V_wFjc4S-kxL8LoWa https://drive.google.com/drive/folders/194_lxE-vy_ha7-5V_wFj... Their YouTube is insanely technical, I think, lots of videos with big equations anyway - https://www.youtube.com/@venusaerospace/videos https://www.youtube.com/@venusaerospace/videos
- growlNark 1y ago> hypersonic This is a meaningless term. There's just varying degrees supersonic. "hyper" implies a completely different thing. EDIT: apparently the military has bastardized the term
- HeatrayEnjoyer 1y agoHypersonic begins at 5x speed of sound.
- lupusreal 1y agoIt's not a new term, and it exists because there are unique practical engineering problems associated with high mach numbers so having a term for this regime is useful even if the distinction seems arbitrary from a pure theoretically perspective.
- growlNark 1y agoSure, but "hyper"? Is there any reason other than that it sounds cooler than "super"? What are we going to do when we hit mach 11, start talking about "hyperhypersonic"? "superhypersonic"?
- magicalhippo 1y agoIt's a distinct regime, so useful to give it a distinc name. Super and hyper are roughly synonyms, but super was already taken. There was also some precedence from wave research back in 1938 which suggested hypersonic and ultrasonic for high frequency waves[1]. At this point it's a well-established term, with 60 years of history[2]. [1]: https://www.ias.ac.in/public/Volumes/seca/007/03/0163-0176.pdf https://www.ias.ac.in/public/Volumes/seca/007/03/0163-0176.p... [2]: https://secwww.jhuapl.edu/techdigest/Content/techdigest/pdf/V35-N04/35-04-Van%20Wie.pdf https://secwww.jhuapl.edu/techdigest/Content/techdigest/pdf/...
- growlNark 1y ago> Super and hyper are roughly synonyms Perhaps you're right in terms of how they're leveraged in today's society. I'll drop my pedantry.
- Havoc 1y agoStill trying to wrap my head around this. Doesn’t this cause insane stresses with basically all explosions being off axis? Or are there multiple sets of explosions moving at same the on opposites sides?
- Tuna-Fish 1y agoThe main drawback is that RDEs need substantially stronger structure to smooth out the forces. It's still worth it, the force of the detonation (it's not separate explosions, it's a single continuous detonation front moving in a circular channel) is small enough to be containable. There have been tests with multiple detonation fronts, but controlling them is much harder. It's very hard to have them go around the channel at exactly the same speed, so their positions relative to each other remain fixed.
- slow_typist 1y agoPlus if the rocket carries a warhead it doesn’t burn for long.
- lupusreal 1y agoJAXA flew one in 2021, to give a sense of developmental pace.
- superkuh 1y agoThis is one of the few hypersonic technologies which could actually be enabling. This is because detonation speeds things up and increases range compared to deflagration (burning) without necessarily needing air-breathing added. This means the craft can remain a simple tapered cone traditional rocket and avoid shockwave imgingement sites on the craft air intakes and the thermal load of that that is so far infeasible to maintain for more than a minute or two.
- pgruenbacher 1y agohttps://youtu.be/QR6iFVj_xHw?feature=shared https://youtu.be/QR6iFVj_xHw?feature=shared Here's a good webinar with some visualization if you're interested in learning more.
- deleted 1y ago[deleted]
- ashoeafoot 1y agoHow do you restart after flameout?
- thebiss 1y agoWatch the Integza video (linked above): The lab interviewed starts the process using a very small pulse detonation engine, which injects a new explosion into the ring.