Autophage rocket engine consumes plastic fuselage for fuel(theengineer.co.uk)
theengineer.co.uk
Autophage rocket engine consumes plastic fuselage for fuel
https://www.theengineer.co.uk/content/news/autophage-rocket-engine-consumes-plastic-fuselage-for-fuel
69 comments
> So it doesn't matter if it makes up 10% of the mass consumed - what matters is how much impulse it provides.
Minimizing the final dry mass at the end of the burn is also very important to maximize delta-v, according to the Tsiolkovsky rocket equation. So it's not just about the impulse provided by the fuel.
Minimizing the final dry mass at the end of the burn is also very important to maximize delta-v, according to the Tsiolkovsky rocket equation. So it's not just about the impulse provided by the fuel.
Yes, the cool thing about this approach is that you can reach extreme vehicle mass ratios without staging. So for example, it could make a single stage to orbit vehicle feasible, on re-entry you replace the cheap consumable "body" and you are ready for another launch.
But it's only an improvement if the fuselage is actually effective in containing the propellant, or is the propellant (imagine a long stick of rocket candy burning at the end, mechanically drawn by a closed nozzle). Otherwise, what you gain in mass ratio you use lose in useful impulse because you need to lift this large mass of mostly inert plastic at launch.
But it's only an improvement if the fuselage is actually effective in containing the propellant, or is the propellant (imagine a long stick of rocket candy burning at the end, mechanically drawn by a closed nozzle). Otherwise, what you gain in mass ratio you use lose in useful impulse because you need to lift this large mass of mostly inert plastic at launch.
>Yes, the cool thing about this approach is that you can reach extreme vehicle mass ratios without staging.
Autophage is, effectively, continuous staging.
Except instead of discarding fuel tanks, they are burned.
>But it's only an improvement if the fuselage is actually effective in containing the propellant, or is the propellant
Well, of course. Which is why it's not something that has been implemented yet, even though people thought of it since the 1930s.
Autophage is, effectively, continuous staging.
Except instead of discarding fuel tanks, they are burned.
>But it's only an improvement if the fuselage is actually effective in containing the propellant, or is the propellant
Well, of course. Which is why it's not something that has been implemented yet, even though people thought of it since the 1930s.
It’s been said that there’s no new ideas in rocketry. Even the most cutting edge stuff was theorized and probably even tested in some rudimentary way by some crazy aerospace engineers in the 50s. They just watched it explode and gave up because rocketry was as much art as science back then - literally throwing stuff against the wall and seeing what explodes (and what explodes a little longer and more usefully).
You also need something that can transfer the thrust to the payload. If you’re burning this thing as an SSTO, it needs to survive being shoved forward at rather more than 1g with payload attached, presumably at the end opposite the nozzle.
I suppose one could attempt a truly exotic design in which the fuel tank gets gasified, piped past the payload, and then burned, thus allowing the tank to be on top, but these seems unlikely to work very well.
I suppose one could attempt a truly exotic design in which the fuel tank gets gasified, piped past the payload, and then burned, thus allowing the tank to be on top, but these seems unlikely to work very well.
>I suppose one could attempt a truly exotic design in which the fuel tank gets gasified, piped past the payload, and then burned, thus allowing the tank to be on top, but these seems unlikely to work very well.
I've been thinking of this design for a long time, but so far it sounds a bit preposterous even for a sci-fi enthusiast with no rocketry knowledge :)
I've been thinking of this design for a long time, but so far it sounds a bit preposterous even for a sci-fi enthusiast with no rocketry knowledge :)
This, a thousand times this - there’s a logarithm in there, folks.
Did you forget about the payload?
I would note the question isn’t should you add more rocket fuel instead of burning the structural mass, it’s can you convert the necessary structural mass into impulse vs being dead mass. You need the structural mass one way or another, and adding more fuel will add structural mass. By burning the structural mass as it becomes less necessary instead of simply ejecting it you maximize delta-v.
Paraffin wax is chemically similar to HDPE and that table puts it at 46MJ/kg, which seems about right.
There have been several small engines that use acrylic housing as combustion chamber and fuel, combined with liquid or gaseous oxygen to form a hybrid rocket engine. None of this sounds new, but I haven't looked deeply into what they're doing here.
What are the exhaust products of HDPE? Any larger molecules will reduce the exhaust velocity, which will lower the specific impulse compared to methane even if they are producing the same amount of energy.
With the correct mixing, water and CO2.
The real question is what is the rate of heavy molecules, or equivalently "how correct is the mixing"?
I imagine those first prototypes weren't that good.
The real question is what is the rate of heavy molecules, or equivalently "how correct is the mixing"?
I imagine those first prototypes weren't that good.
Perfect combustion yields H2O and CO2, same as methane.
Wow, fascinating! From the title I was envisioning something akin to a solid rocket motor where the fuel gets consumed from the inside out and wondering what the point of that was, since at the end of the burn you'd still need to have enough fuselage left to avoid compromising structural integrity. (And at that point why not just build the fuselage like that from the start and use the extra mass for more liquid fuel?) But from the video it looks like this engine actually burns the hull back to front, meaning the fuselage actually gets shorter throughout the course of the flight until there's nothing left. That's really cool!
Yes I was absolutely not expecting a hot glue gun with a jet of flame coming out of the nozzle instead of hot glue, but that’s essentially what it looked like.
Is the idea that in a vertical version of this the motive force pushing the stack into the nozzle would be provided from the rocket's own acceleration?
Would that negate some of the controlability characteristics?
And would it need to be carefully tuned to the launch profile? (I assume deviations wouldn't be self-correcting eg. if acceleration is reduced there's less injection force presumably leading to less thrust).
Would that negate some of the controlability characteristics?
And would it need to be carefully tuned to the launch profile? (I assume deviations wouldn't be self-correcting eg. if acceleration is reduced there's less injection force presumably leading to less thrust).
You could probably put some low effort cables from the engine to the top of the stack and add pressure as needed without too much effort
I had the same reaction, then watched the video after reading your post. So cool. Excellent catastrophic failure at the end too :)
Yeah gotta work out that snag ;-). Could always stage the booster just before booster.
> The concept of a self-eating rocket engine was first proposed and patented in 1938. However, no autophage engine designs were fired in a controlled manner until a research partnership between Glasgow University and Dnipro National University, Ukraine achieved this milestone in 2018.
Is this true? I've seen many hobby hybrid rockets built in this fashion over the years, for example acrylic tube + oxygen gas. Maybe none of them were ever launched.
https://www.youtube.com/watch?v=VI8gdmjEwKc
It's pretty much the easiest way to do a hybrid rocket.
Is this true? I've seen many hobby hybrid rockets built in this fashion over the years, for example acrylic tube + oxygen gas. Maybe none of them were ever launched.
https://www.youtube.com/watch?v=VI8gdmjEwKc
It's pretty much the easiest way to do a hybrid rocket.
Right, but there you're either putting the acrylic in an extra structural tube, or you're using an acrylic tube which is hugely thicker than necessary so you can leave a substantial unburned shell there as the structure.
The outer part which is acting as structure cannot be burned as fuel because it's necessary as structure, and if you let the burn continue too long, it would cause the rocket to fail. When the burn ends, there's a lot of unburned acrylic still there.
This design allows a given piece of tube to first serve as structure, and then later serve as fuel, ostensibly ending the burn having consumed the whole tube with no structure left behind except perhaps a bit stuck in the feed mechanism. That's novel.
The outer part which is acting as structure cannot be burned as fuel because it's necessary as structure, and if you let the burn continue too long, it would cause the rocket to fail. When the burn ends, there's a lot of unburned acrylic still there.
This design allows a given piece of tube to first serve as structure, and then later serve as fuel, ostensibly ending the burn having consumed the whole tube with no structure left behind except perhaps a bit stuck in the feed mechanism. That's novel.
I thought there were more examples of hybrid engines?
https://en.wikipedia.org/wiki/RocketMotorTwo
Also, I wonder how complex this is going to make the aerodynamic controls. You are losing moment arms between engine and the forward surfaces, if they exist.
https://en.wikipedia.org/wiki/RocketMotorTwo
Also, I wonder how complex this is going to make the aerodynamic controls. You are losing moment arms between engine and the forward surfaces, if they exist.
>The Ouroborous-3 uses high-density polyethylene plastic tubing as its autophagic fuel source, burning it alongside the rocket’s mix of gaseous oxygen and liquid propane.
Bonus points for naming.
Bonus points for naming.
Promin Aerospace, a Ukrainian company founded by a friend of mine, has been working on the same technology. Interesting to see this take on it though, it's an idea that seems almost too fantastical to work.
The other advantage is this is a solid rocket that can shut be turned off.
That’s usually the major drawback to solid rockets.
(Apologies if that’s obvious)
That’s usually the major drawback to solid rockets.
(Apologies if that’s obvious)
Weirdly there are solid fuel rockets that can be turned on and off.
Electric solid propellants (ESPs) is the term apparently. I saw youtube video where some guy was fooling around with the some brand or another of this type.
see https://ntrs.nasa.gov/api/citations/20190030421/downloads/20...
Electric solid propellants (ESPs) is the term apparently. I saw youtube video where some guy was fooling around with the some brand or another of this type.
see https://ntrs.nasa.gov/api/citations/20190030421/downloads/20...
here's the video of ESP's that I saw
https://www.youtube.com/watch?v=eHRyv7ARb5M
https://www.youtube.com/watch?v=eHRyv7ARb5M
Oxygen/Acrylic engines are popular on YouTube, most likely because they look great on film - https://www.youtube.com/watch?v=TLPWqCMb7DE
I wonder if it'd be possible to design the body in such a way that the nozzle shape changed as the rocket rose through the atmosphere, so that the nozzle was continuously optimized for ambient air pressure.
Hm, you normally need more nozzle (/bell) as you ascend. I'm not sure how to square this with autophagy but if you figure it out I will subscribe to your newsletter.
Burning plastic sounds like an environmental hazard which is completely unaddressed in the article. At full scale, the communities near the launch site will never accept it.
There's a massive difference between HDPE (which is a hydrocarbon) and PVC (which contains chlorine and is awful to burn). Might be some plasticizers in the mix as well, but mostly they're just H, C, and O. Cl makes the real nasty stuff.
Rocket fuels can have some pretty nasty stuff in them as well, of course...
Rocket fuels can have some pretty nasty stuff in them as well, of course...
Some plastics can burn cleanly.
The whole "don't burn plastic" only applies if you don't know what type the plastic is.
The whole "don't burn plastic" only applies if you don't know what type the plastic is.
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I see you've bought into the whole "plastics = bad" trend, but not all plastics are the same.
Pure HDPE is just H and C, basically like candle wax with a much higher molecular weight. Products of combustion are H2O and CO2.
Chlorinated and fluorinated plastics are the ones that produce lots of toxic emissions when burned.
Pure HDPE is just H and C, basically like candle wax with a much higher molecular weight. Products of combustion are H2O and CO2.
Chlorinated and fluorinated plastics are the ones that produce lots of toxic emissions when burned.
Why is burning plastic worse than the existing fuels? Pretty much all fuel mixes for rockets are nasty stuff.
Most fuel mixes for rockets are just Kerosene and Liquid Oxygen, at least in the USA. Seems like most of the next generation are aiming for Methane and LOX.
Burning plastic incompletely would most likely produce more noxious stuff than Kerolox or Methalox engines. Maybe on par with existing Solid Rockets or Hypergolics.
Burning plastic incompletely would most likely produce more noxious stuff than Kerolox or Methalox engines. Maybe on par with existing Solid Rockets or Hypergolics.
Rockets leave the launch site very quickly. And they launch from the shore towards the ocean.
No one is allowed to be near the launch path or within 2-3 miles of the launch.
No one is allowed to be near the launch path or within 2-3 miles of the launch.
What's the difference to other fuels? Except for few plastic is actually much better...
Looks like an esg play, in practice energy density matters a lot more, if you can’t beat regular rocket fuel, it’s pretty pointless
"looks like an esg"
Go read the rest of the thread where they discuss the very technical reasons this is cool.
What kind of world do you live in where you equate ESG with being harmful? Sounds like "conservative uncle who doesn't know anything about the topic".
Go read the rest of the thread where they discuss the very technical reasons this is cool.
What kind of world do you live in where you equate ESG with being harmful? Sounds like "conservative uncle who doesn't know anything about the topic".
> What kind of world do you live in where you equate ESG with being harmful?
ESG in principle isn't harmful, but it does seem to attract grifters that game one or two of the E/S/G letters to make their firms appear more socially responsible:
ESG in principle isn't harmful, but it does seem to attract grifters that game one or two of the E/S/G letters to make their firms appear more socially responsible:
https://www.bloomberg.com/opinion/articles/2023-07-12/it-s-easy-to-make-oil-companies-esg
https://www.offshore-technology.com/features/revealed-the-oil-gas-companies-leading-the-way-in-esg-2/
https://www.ey.com/en_us/oil-gas/what-if-oil-and-gas-operators-view-esg-as-a-catalyst-for-innovationAt the rate plastic particles are piling up, you'd think a rocket like this could just pull plastic from the atmosphere.
Neat, but I don't understand how this would work if actually contained the fuel tanks.
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Finally a rocket engine that is engine-rich by design.
US High Power Rocketry people have been fly these (NO and plastic) since the late 90s - this certainly isn't the first of its type
The text of the article totally fails to mention that the rocket blew up fairly spectacularly 1 minute 30 into the test...
See the video.
See the video.
If your first test doesn't fail, then you're missing an opportunity to collect extremely valuable data.
The discussion in the comments indicates that the test included a run outside of it's operational range for pulsed firing, with the intent to see how it would react.
Stressing components to destruction is a commonplace product development activity, including rocketry.
Props to Glasgow U for showing exactly that. It takes confidence to show how you make sausage.
Green movement for space?
Can we just name this a rocket candle?
Cute, but what is the point of this?
At the very best it could stop SSTO to orbit suck so much. But it seems SpaceX is far enough that it is not possible to get close to the efficiency with an autophage rocket. It maybe was possible as long as first stage was always destined to crash, but when it can land safely the entire efficiency equation got turned on its head.
Would that kind of rocket be usable for deep space (basically -- improve thrust to weight by eliminating the weight of the fuselage as you thrust)? I also don't think so. For space, much higher specific impulse engines exist than any kind of fuselage material that can burn itself.
So I just don't see any use of this.
At the very best it could stop SSTO to orbit suck so much. But it seems SpaceX is far enough that it is not possible to get close to the efficiency with an autophage rocket. It maybe was possible as long as first stage was always destined to crash, but when it can land safely the entire efficiency equation got turned on its head.
Would that kind of rocket be usable for deep space (basically -- improve thrust to weight by eliminating the weight of the fuselage as you thrust)? I also don't think so. For space, much higher specific impulse engines exist than any kind of fuselage material that can burn itself.
So I just don't see any use of this.
The point is simple.
The delta-V per rocket stage is governed by the Tsiolkovsky equation:
dv = Isp * g0 * ln(m_start/m_end)
So, if m_end goes to zero, you get a significant dv gain.
It has absolutely nothing to do with the "efficiency" of returning a stage or not.
The delta-V per rocket stage is governed by the Tsiolkovsky equation:
dv = Isp * g0 * ln(m_start/m_end)
So, if m_end goes to zero, you get a significant dv gain.
It has absolutely nothing to do with the "efficiency" of returning a stage or not.
Your comment is needlessly dismissive about a benchtop experiment that doesn't really compare to something like Starship and the engines that it uses.
This is really neat. It doesn't have to be groundbreaking to be really cool, but who knows maybe one day it will be.
This is really neat. It doesn't have to be groundbreaking to be really cool, but who knows maybe one day it will be.
Indeed many (most?) technology breakthroughs and great products start as "garage" experiments.
- Aviation didn't start with someone rolling out a 747, it started with the Wright Flyer - something that barely flew with just the right winds.
- Apple, Inc. literally started in a garage with an 8-bit computer with 8k ram and you had to provide your own case and power supply, monitor, and keyboard.
- The early stages of modern rocket technology looked not much different than this experiment: Here's a video of Goddard testing at his Aunt's farm:
https://upload.wikimedia.org/wikipedia/commons/transcoded/a/...
> "The neighbors complained"
- Aviation didn't start with someone rolling out a 747, it started with the Wright Flyer - something that barely flew with just the right winds.
- Apple, Inc. literally started in a garage with an 8-bit computer with 8k ram and you had to provide your own case and power supply, monitor, and keyboard.
- The early stages of modern rocket technology looked not much different than this experiment: Here's a video of Goddard testing at his Aunt's farm:
https://upload.wikimedia.org/wikipedia/commons/transcoded/a/...
> "The neighbors complained"
From the paper's abstract:
> This both increases the maximum payload mass of a launch system and allows for the miniaturization of launch vehicles so they may be used as nano-launchers for the rapid access of small satellites to low-earth orbit.
> This both increases the maximum payload mass of a launch system and allows for the miniaturization of launch vehicles so they may be used as nano-launchers for the rapid access of small satellites to low-earth orbit.
Sounds great for weapons applications. :-/ Small tube which can reach as far as orbit.
Re-usabilitity is "not needed".
Re-usabilitity is "not needed".
Might be useful in a Mars sample return sort of scenario.
As I said, it reduces problems of SSTO (Single Stage To Orbit). The problem of SSTO is low payload mass to the size of the rocket and fuel necessary to transport it. The main solution to this is having multiple stages. Which comes with its own problems -- multiple engines, complexity, more points of failure, etc.
But in the meantime SpaceX learned to reuse the stages so suddenly the problems are no longer as much of a problem as they were before.
But in the meantime SpaceX learned to reuse the stages so suddenly the problems are no longer as much of a problem as they were before.
> Cute, but what is the point of this?
There isn't much point. I don't know an application where other approaches wouldn't be superior.
There isn't much point. I don't know an application where other approaches wouldn't be superior.
> A conventional rocket’s structure makes up between five and 12 per cent of its total mass. Our tests show that the Ouroborous-3 can burn a very similar amount of its own structural mass as propellant.
It seems like they are measuring the wrong thing.
Rocket fuselage isn't as good a fuel as, well, rocket fuel. So it doesn't matter if it makes up 10% of the mass consumed - what matters is how much impulse it provides.
However! HDPE is reasonably competitive with methane. While it doesn't make Wikipedia's list [0] of hundreds of potential fuels by calorific value, which puts methane at 55 MJ/kg, research in municipal waste incineration puts polyethylene around 43 MJ/kg [1]. And in fact it's already been studied in Japan as a rocket fuel [2] using N2O as an oxidiser. So this seems completely plausible.
[0] https://en.wikipedia.org/wiki/Heat_of_combustion
[1] https://www.researchgate.net/publication/336848986_Productio...
[2] https://www.mdpi.com/2226-4310/6/4/45