I have some hope that rotating detonation engines will make aerospikes viable. But I don’t even see them mentioned in this paper.
The idea with the constantly moving flame front is that it spreads the heat out. The limitation with aerospikes is getting enough coolant through the spike. Bells are simpler to cool, which as I understand more than makes up for them needing more cooling.
I think they were mentioned briefly. Aerospikes can work with rdes potentially if the certain versions catch on, but at the end of the day the heat fluxes are even worse for the detonation based engines. The main reason aerospikes don’t make sense is that you adding more area that gets the highest amount of heat flux and your plumbing and cooling jackets becomes a nightmare.
I wonder if aerospikes were popular as an idea in the J-2 engine ~Apollo era since USA only had gas generator engines (and expander RL-10).
You can't get to very high chamber pressures with those, and then maybe aerospike was a way to work around the limitations.
Then XLR-129 and SSME came along with staged combustion cycle and you can just have higher pressure engines. They can both run at sea level and still have a decent efficiency in vacuum.
The linear aerospike for X-33 was kind of a neat tech demo and fit in with the whole shape of the vehicle and composites, non-tubular tanks and large base area. Maybe too many new things at once in retrospect.
Doesn't seem like a front rotating around the spike would gain that much "spreading out" over a continuous front. At the end of the day, its a spike that narrows to a very small point.
RDEs are far less tested than aerospikes. (In part because you can build a dipshit aerospike in your garage. I don’t know anyone who has made an RDE at home.)
The abstract brings up SSTOs, but has there been anything in recent invention that will make them anything other than the white whale people have been chasing since forever?
Source: worked at a startup that took over the patents for the X-33 next gen shuttle and VentureStar SSTO (aerospike design!)
The Columbia disaster really set back SSTO appetite. Probably the whole reason we got the patents, truly.
SSTOs are, like everything else going to orbit, delimited by weight.
If you are going to make the fuel tanks internal to the vehicle and not something that falls off and sheds their weight mid-flight, you have to get vehicle weight to the absolute minimum. Losing weight has second order effects because it means you now have to carry less fuel so you now have a smaller fuel tank which means the tank weighs less which means you get to carry less fuel… etc.
The key, IMO, is material science advancements, specifically around plastics and composites. Very efficient engine design is matters too, but if you can just bring less mass up with you you can start to approach an achievable fuel weight.
It’s a hard job, you need plastics that can handle orbital temperature cycling (+300 to -300 F every 30 mins), atomic oxygen (nasty corrosion), UV with no atmospheric protection, FST for crew exposure…
Exotic metal alloys can get you around some of these problems, but they can be difficult and expensive to work with. Same issue with high-performance polymers. No free lunches here.
With 3D printing of metals and high-performance composites, you can probably remove additional weight so there’s some light in that tunnel.
But all in all it’s very hard to get out of the gravity well with your fuel in tow and survive the extremes of space. My belief is the first vehicle to pull it off will look like a Swiss cheese of voids and lattices from printing / honeycombs and be made almost entirely out of plastic and carbon fiber.
The 1990s were a lost decade for reusable space flight because instead of chasing incremental improvements to the Space Shuttle (an orbiter with reusable tiles that could be turned around in days, not months) or something like the Falcoln 9 or the fly-back version of Saturn V that O'Neill's students drew in 1979, it was all about SSTO.
SSTO is just marginally possible, if it is possible you need exotic materials and engines and you're never going to get a good payload fraction and adding wings, horizontal takeoff, horizontal landing and such just makes it worse. The one good thing about it is that you get closer to "aircraft-like operations" because in principle you can inspect it, refill it, and relaunch it -- whereas something like the STS or Falcoln 9 or Starship will require stacking up multiple parts for each launch.
My guess is aerospikes are making a comeback though because of interest in hypersonic weapons system. I could also see them being useful for the second stage of something like Starship which mostly operates at high altitudes but has to land at low altitudes. There are a lot of other technical problems, like the thermal management system, which really have to be solved before worrying about that optimization.
Currently the Starship upper stage simply has two different sets of bell nozzles: Three engines with nozzles for atmospheric pressure, and three for vacuum. I wonder how inefficient this really is compared to having just aerospike nozzles.
This. In my very uninformed opinion the only way we'll get useful SSTO is if we can get a meaningful amount of oxygen from the atmosphere rather than carrying it up in heavy tanks. The failure of Reaction Engines with their SABRE engine is disappointing on this front.
doesn't scale well. The amount of air entering is proportional to square - cross-section - while the mass of rocket is cubic. While scramjet/turbojet/air-augmentation, say as a separate detachable stage, can be pretty efficient for smaller rocket, anything making significant improvement for say Starship would looks like a fat monster cross-section-wise with tremendous hardware cost and weight loosing outright to the straight option of adding additional tanks and rocket engines.
Wrt. aerospike engine - sounds nice, yet hardware wise it is heavier than the classic engine, and just look at that large number of pieces - just all those small mini-engines - it is made of and compare to Raptor 3. And for the optimal expansion - i'm waiting somebody will add a dynamically adjusting telescopic kind of end section to the classic bell nozzle.
A napkin to illustrate. Lets say you add a Raptor and 80 tons of fuel plus oxygen for it. That will give you 100 seconds of excess impulse of at least 160 tons (240 ton of thrust minus 80 tons) at the beginning to 240 tons at the end, so roughly 100 seconds of 200 tons. To get 200 tons thrust you'd need 20 fighter turbojet engines capable of at least Mach 3 - that is cost, complexity and weight dwarfing that one Raptor engine.
For scramjet, assuming we got a decent one, napkin is about the same. The best, my favorite, is air-augmented - scram-compress the air and channel it on the outside of the hot bell nozzles of the already working rocket engines - unfortunately the scaling mentioned above comes into play for meaningfully sized rockets though it has worked great for small ones.
Why make an SSTO when you can make a TSTO? First stage recovery is a solved problem and will always greatly relax the engineering problems over making a SSTO.
The article has a link (citation 17) to a site selling toy models of that vehicle as an image source, I can find one (fourth image in the gallery) there where it sorta looks like the wing is missing because the wing is black against a black background but it's not the same image shown in the paper:
The name "Venturestar" is properly rendered in that image but "NASA" and "Lockheed Martin" are thoroughly mangled the way I'd expect text to be mangled in an AI image. The image from the toy site could have been used as as reference image to create the image in the paper one way or another.
Yes, if you look close, the paper is replete with error-filled generative reproductions of existing illustrations in the citations; including Fig. 6 (MC Escher struts), Fig. 7 (sprouting greeble tubes), and Fig. 8 (actuators replaced by tubes connected to mystery manifolds).
Even Fig. 2 shows the spike geometry magically changing, which is not addressed in the text and seems like an error carried over from the original illustration in the cited source.
Casts serious doubt on the credibility of the rest of the work.
I have some hope that rotating detonation engines will make aerospikes viable. But I don’t even see them mentioned in this paper.
The idea with the constantly moving flame front is that it spreads the heat out. The limitation with aerospikes is getting enough coolant through the spike. Bells are simpler to cool, which as I understand more than makes up for them needing more cooling.
I think they were mentioned briefly. Aerospikes can work with rdes potentially if the certain versions catch on, but at the end of the day the heat fluxes are even worse for the detonation based engines. The main reason aerospikes don’t make sense is that you adding more area that gets the highest amount of heat flux and your plumbing and cooling jackets becomes a nightmare.
I wonder if aerospikes were popular as an idea in the J-2 engine ~Apollo era since USA only had gas generator engines (and expander RL-10).
You can't get to very high chamber pressures with those, and then maybe aerospike was a way to work around the limitations.
Then XLR-129 and SSME came along with staged combustion cycle and you can just have higher pressure engines. They can both run at sea level and still have a decent efficiency in vacuum.
The linear aerospike for X-33 was kind of a neat tech demo and fit in with the whole shape of the vehicle and composites, non-tubular tanks and large base area. Maybe too many new things at once in retrospect.
Doesn't seem like a front rotating around the spike would gain that much "spreading out" over a continuous front. At the end of the day, its a spike that narrows to a very small point.
RDEs are far less tested than aerospikes. (In part because you can build a dipshit aerospike in your garage. I don’t know anyone who has made an RDE at home.)
The abstract brings up SSTOs, but has there been anything in recent invention that will make them anything other than the white whale people have been chasing since forever?
Source: worked at a startup that took over the patents for the X-33 next gen shuttle and VentureStar SSTO (aerospike design!)
The Columbia disaster really set back SSTO appetite. Probably the whole reason we got the patents, truly.
SSTOs are, like everything else going to orbit, delimited by weight.
If you are going to make the fuel tanks internal to the vehicle and not something that falls off and sheds their weight mid-flight, you have to get vehicle weight to the absolute minimum. Losing weight has second order effects because it means you now have to carry less fuel so you now have a smaller fuel tank which means the tank weighs less which means you get to carry less fuel… etc.
The key, IMO, is material science advancements, specifically around plastics and composites. Very efficient engine design is matters too, but if you can just bring less mass up with you you can start to approach an achievable fuel weight.
It’s a hard job, you need plastics that can handle orbital temperature cycling (+300 to -300 F every 30 mins), atomic oxygen (nasty corrosion), UV with no atmospheric protection, FST for crew exposure…
Exotic metal alloys can get you around some of these problems, but they can be difficult and expensive to work with. Same issue with high-performance polymers. No free lunches here.
With 3D printing of metals and high-performance composites, you can probably remove additional weight so there’s some light in that tunnel.
But all in all it’s very hard to get out of the gravity well with your fuel in tow and survive the extremes of space. My belief is the first vehicle to pull it off will look like a Swiss cheese of voids and lattices from printing / honeycombs and be made almost entirely out of plastic and carbon fiber.
The 1990s were a lost decade for reusable space flight because instead of chasing incremental improvements to the Space Shuttle (an orbiter with reusable tiles that could be turned around in days, not months) or something like the Falcoln 9 or the fly-back version of Saturn V that O'Neill's students drew in 1979, it was all about SSTO.
SSTO is just marginally possible, if it is possible you need exotic materials and engines and you're never going to get a good payload fraction and adding wings, horizontal takeoff, horizontal landing and such just makes it worse. The one good thing about it is that you get closer to "aircraft-like operations" because in principle you can inspect it, refill it, and relaunch it -- whereas something like the STS or Falcoln 9 or Starship will require stacking up multiple parts for each launch.
My guess is aerospikes are making a comeback though because of interest in hypersonic weapons system. I could also see them being useful for the second stage of something like Starship which mostly operates at high altitudes but has to land at low altitudes. There are a lot of other technical problems, like the thermal management system, which really have to be solved before worrying about that optimization.
> SSTO is just marginally possible, if it is possible
Looking at the specs it would appear the first stage of a Falcon 9 plus a nosecone could get itself to orbit with no cargo. Barely.
Currently the Starship upper stage simply has two different sets of bell nozzles: Three engines with nozzles for atmospheric pressure, and three for vacuum. I wonder how inefficient this really is compared to having just aerospike nozzles.
5 replies →
There has been some progress on scramjet propulsion.
This. In my very uninformed opinion the only way we'll get useful SSTO is if we can get a meaningful amount of oxygen from the atmosphere rather than carrying it up in heavy tanks. The failure of Reaction Engines with their SABRE engine is disappointing on this front.
7 replies →
doesn't scale well. The amount of air entering is proportional to square - cross-section - while the mass of rocket is cubic. While scramjet/turbojet/air-augmentation, say as a separate detachable stage, can be pretty efficient for smaller rocket, anything making significant improvement for say Starship would looks like a fat monster cross-section-wise with tremendous hardware cost and weight loosing outright to the straight option of adding additional tanks and rocket engines.
Wrt. aerospike engine - sounds nice, yet hardware wise it is heavier than the classic engine, and just look at that large number of pieces - just all those small mini-engines - it is made of and compare to Raptor 3. And for the optimal expansion - i'm waiting somebody will add a dynamically adjusting telescopic kind of end section to the classic bell nozzle.
A napkin to illustrate. Lets say you add a Raptor and 80 tons of fuel plus oxygen for it. That will give you 100 seconds of excess impulse of at least 160 tons (240 ton of thrust minus 80 tons) at the beginning to 240 tons at the end, so roughly 100 seconds of 200 tons. To get 200 tons thrust you'd need 20 fighter turbojet engines capable of at least Mach 3 - that is cost, complexity and weight dwarfing that one Raptor engine.
For scramjet, assuming we got a decent one, napkin is about the same. The best, my favorite, is air-augmented - scram-compress the air and channel it on the outside of the hot bell nozzles of the already working rocket engines - unfortunately the scaling mentioned above comes into play for meaningfully sized rockets though it has worked great for small ones.
There's been progress on scramjets for cruise missions. For acceleration missions, like launchers, scramjets make no sense at all.
4 replies →
Why make an SSTO when you can make a TSTO? First stage recovery is a solved problem and will always greatly relax the engineering problems over making a SSTO.
Because of course SSTO has benefits over TSTO, simplicity of operation being one example.
3 replies →
video on the rectangular one https://www.youtube.com/watch?v=FcW9kUUTfxY
I'm not sure if this one counts but recent https://www.youtube.com/watch?v=UShD03eG9IU
Is that an AI generated image of the Venture Star? It's missing portside wings..
Gotta be, the skunk logo is an approximation of the real one.
The article has a link (citation 17) to a site selling toy models of that vehicle as an image source, I can find one (fourth image in the gallery) there where it sorta looks like the wing is missing because the wing is black against a black background but it's not the same image shown in the paper:
https://fantastic-plastic.com/lockheed-martin-x-33-venturest...
The name "Venturestar" is properly rendered in that image but "NASA" and "Lockheed Martin" are thoroughly mangled the way I'd expect text to be mangled in an AI image. The image from the toy site could have been used as as reference image to create the image in the paper one way or another.
Yes, if you look close, the paper is replete with error-filled generative reproductions of existing illustrations in the citations; including Fig. 6 (MC Escher struts), Fig. 7 (sprouting greeble tubes), and Fig. 8 (actuators replaced by tubes connected to mystery manifolds).
Even Fig. 2 shows the spike geometry magically changing, which is not addressed in the text and seems like an error carried over from the original illustration in the cited source.
Casts serious doubt on the credibility of the rest of the work.
I thought this would be about the key-value store, Aerospike.
Pretty neat, my dad worked on that X-33 program at Lockheed.
cool contribution from a top Colombian university researchers