[HN Gopher] Autophage rocket engine consumes plastic fuselage fo...
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Autophage rocket engine consumes plastic fuselage for fuel
Author : timthorn
Score : 92 points
Date : 2024-01-12 15:41 UTC (7 hours ago)
(HTM) web link (www.theengineer.co.uk)
(TXT) w3m dump (www.theengineer.co.uk)
| onetimeuse92304 wrote:
| 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.
| timthorn wrote:
| 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.
| actionfromafar wrote:
| Sounds great for weapons applications. :-/ Small tube which
| can reach as far as orbit.
|
| Re-usabilitity is "not needed".
| ceejayoz wrote:
| Might be useful in a Mars sample return sort of scenario.
| onetimeuse92304 wrote:
| 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.
| Teever wrote:
| 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.
| kloch wrote:
| 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"
| Teever wrote:
| http://www.zenpencils.com/comic/64-robert-h-goddard-the-
| rock...
| fransje26 wrote:
| 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.
| bugbuddy wrote:
| 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.
| AzuraIsCool wrote:
| What's the difference to other fuels? Except for few plastic is
| actually much better...
| zdragnar wrote:
| Why is burning plastic worse than the existing fuels? Pretty
| much all fuel mixes for rockets are nasty stuff.
| AlgorithmicTime wrote:
| 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.
| bilsbie wrote:
| 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.
| londons_explore wrote:
| Some plastics can burn cleanly.
|
| The whole "don't burn plastic" only applies if you don't know
| what type the plastic is.
| phyzome wrote:
| 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...
| ajuc wrote:
| > 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.
| mechhacker wrote:
| 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.
| myself248 wrote:
| 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.
| dmurray wrote:
| > with the plastic fuselage supplying up to one-fifth of the
| total propellant used.
|
| > 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
| MPSimmons wrote:
| 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.
| wcoenen wrote:
| > _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.
| pletnes wrote:
| This, a thousand times this - there's a logarithm in there,
| folks.
| IshKebab wrote:
| Did you forget about the payload?
| metabagel wrote:
| Isn't the payload pretty inconsequential in comparison
| with the total weight of fuel at launch?
| IshKebab wrote:
| It's not inconsequential in comparison with the total
| weight of the rocket at the end. That's what we're
| talking about.
| cornholio wrote:
| 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.
| fnordpiglet wrote:
| 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.
| whatever1 wrote:
| Green movement for space?
| bilsbie wrote:
| 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)
| hackeraccount wrote:
| 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...
| hackeraccount wrote:
| here's the video of ESP's that I saw
|
| https://www.youtube.com/watch?v=eHRyv7ARb5M
| Ajedi32 wrote:
| 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!
| brokencode wrote:
| 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.
| thenickevans wrote:
| I had the same reaction, then watched the video after reading
| your post. So cool. Excellent catastrophic failure at the end
| too :)
| londons_explore wrote:
| 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.
| vlachen wrote:
| 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.
| stronglikedan wrote:
| If your first test _doesn 't_ fail, then you're missing an
| opportunity to collect _extremely_ valuable data.
| inopinatus wrote:
| Stressing components to destruction is a commonplace product
| development activity, including rocketry.
| dtgriscom wrote:
| Props to Glasgow U for showing exactly that. It takes
| confidence to show how you make sausage.
| ortusdux wrote:
| Oxygen/Acrylic engines are popular on YouTube, most likely
| because they look great on film -
| https://www.youtube.com/watch?v=TLPWqCMb7DE
| m3kw9 wrote:
| 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
| hiddencost wrote:
| "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".
| science4sail wrote:
| > 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:
| 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-
| innovation
| Cyclical wrote:
| 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.
| 1970-01-01 wrote:
| >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.
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