
A 'self-eating' rocket engine could put satellites in orbit more easily - curtis
https://phys.org/news/2018-05-aim-stars-rocket.html
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pecanpie
Here's the paper, complete with a cutaway diagram of the engine:
[https://eprints.gla.ac.uk/155610/7/155610.pdf](https://eprints.gla.ac.uk/155610/7/155610.pdf)

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azernik
Much more sane than the phys.org write-up. The advantage of this isn't "would
consume its own structure during ascent" (what does that even mean??), it's
that this would have the simplicity, cost, and storability of a solid rocket
with the throttleability of a liquid rocket.

(Side note: Great caption on figure 5. "Second firing. The engine was
extinguished by an explosion at 142s.")

~~~
Luc
Phys.org is a low value website that republishes press releases, in this case
this one:
[https://www.gla.ac.uk/news/headline_586616_en.html](https://www.gla.ac.uk/news/headline_586616_en.html)

~~~
azernik
Aaaah. Didn't know the source.

Also, I find it funny that it's the UK partner that published the press
release and the paper, even though the actual research was done in Ukraine
(where there's a lot of Soviet space industry legacy) and the paper seems to
indicate that the Glasgow contribution was just to give them modern
instrumentation.

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chroem-
This is pretty neat. It would make staging and reusability a moot point if the
entire launch vehicle was an engine attached to an expendable fuel rod with a
payload adapter on top. You could recover the engine fairly easily since it's
so compact. Not sure about the Isp of polyethylene fuels though.

~~~
tim333
Aluminium is decent fuel as used in NASAs solid boosters. Now if they could
just find a way to grind up the structure and stick it in the engine.

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IX-103
How strong would the fuel rod and motor have to be? Since they are the only
structural components it seems like they would have to bear the full thrust of
the rocket:

The fuel rod is not bolted to engine, so the pressure in the combustion
chamber is transmits the force upward. The motor must be attached to
combustion chamber so the interface between the motor and fuel rod must
counter all that force to keep the rod in the chamber.

~~~
Someone
The text repeatedly talks about small satellites/cubesats.

I think that’s essential.

~~~
woodandsteel
Where is the satellite? Is there a framework that holds it above the fuel rod,
or what?

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DuskStar
This seems to be a solid rocket booster with moving parts. Isn't that the
worst of both worlds? Lower ISP than liquid fuelled rockets due to the
propellant choices and higher manufacturing complexity than a solid rocket
booster...

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1053r
The number one thing you worry about with a launch vehicle is not ISP, it's
the tyranny of the rocket equation. We have tech with VERY high ISP (ion
drives, for example), but we can't use them until our vehicles hit space
because of the extremely low maximum thrust.

Meanwhile the high thrust options we have are all very heavy, which means we
have to carry more fuel, which means we need a bigger rocket, which means have
to carry more fuel, and so on. The sum of this infinite series is finite, but
it is still large.

If this tech lowers the weight of the first stage, it might actually RAISE the
ISP of the rocket overall, even if it lowers the ISP of the engine itself.

~~~
Maybestring
>The number one thing you worry about with a launch vehicle is not ISP, it's
the tyranny of the rocket equation.

The rocket equation doesn't account for thrust. It's terms are mass and ISP
(or exhaust velocity).

>If this tech lowers the weight of the first stage, it might actually RAISE
the ISP of the rocket overall, even if it lowers the ISP of the engine itself.

ISP is depends _only_ on exhaust velocity. Changing the mass of the rocket
cannot effect it.

~~~
amluto
> The rocket equation doesn't account for thrust. It's terms are mass and ISP
> (or exhaust velocity).

Only sort of true. If you naively apply the rocket equation like you're
imagining, you would predict a nonzero final velocity for a hypothetical
rocket that has enormous ISP but thrust less than its weight. This is true if
the rocket is starting out in orbit, but it's totally wrong when you're on the
ground. Starting from the ground, you also have to fight gravity, so you care
more about (thrust - weight) / mass.

~~~
IshKebab
Sure, but "the rocket equation" is 100% talking about the classic ideal rocket
equation, which I just discovered is also called the Tsiolkovsky rocket
equation.

[https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation](https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation)

If you want to be more specific, e.g. include gravity then you can't say "the
rocket equation".

~~~
robotrout

        > If you want to be more specific, e.g. include gravity 
        > then you can't say "the rocket equation".
    

You may not be able to say "the rocket equation" in that context, but NASA
does. [1]

[1]
[https://www.nasa.gov/mission_pages/station/expeditions/exped...](https://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html)

~~~
Maybestring
Despite Don mentioning gravity along with deltaV he is obviously attempting to
describe the classic rocket equation without scaring people away with the
math.

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neaanopri
How are they going to get a good seal around the rod at it was being consumed?
That sounds like it would limit the thrust the engine can achieve.

~~~
mark-r
The engine is exerting tremendous pressure against the rod, wouldn't that
help?

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jimrandomh
This article doesn't answer the question every Kerbal Space Program player
wants to know: what's the I_sp?

~~~
azernik
At the engine design phase, they care about a different number: chamber
pressure.

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acou_nPlusOne_t
Only slightly related, but are there news on the concept of not taking the
energy necessary along at all?

[https://en.wikipedia.org/wiki/Beam-
powered_propulsion](https://en.wikipedia.org/wiki/Beam-powered_propulsion)

This was hyped for a time, but then silence returned. Anyone got insider
infos?

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lainga
It's a giant round of caseless ammunition? Neat!!

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greypowerOz
how would the shrinking "body of the rocket" ie fuel be able to
withstand/transfer the thrust/load/accelleration force safely to the rest of
the rocket stack?

i mean to say its a 3 to 5-ish G load or something like that, and vibration
alone would be...interesting...

~~~
neaanopri
One thing i saw was that the rocket can throttle, presumably by changing the
rate at which the fuel rod is moved inwards.

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Andhurati
How hazardous would igniting the fuel-shell be? How much larger do the engines
have to be, if they have to be at all, to consume two different types of fuel?

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TangoTrotFox
It's not two different types of fuel and all rockets do this. It's an oxidizer
and a fuel. For instance a common rocket fuel is liquid hydrogen and liquid
oxygen. React the two and you get energy in the process... and water. So for
instance most of the space shuttle's main engine exhaust was water vapor!
Quite counter intuitive.

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outworlder
Yeah, water is hydrogen dust :)

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whatsstolat
Hydrogen rust

~~~
mark-r
Hydrogen ash?

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5DFractalTetris
It's all about self-refueling self-replicating water-burning probes. Map the
Oort Cloud like that and you'll make a penny!!

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kuwze
I was hoping this would be about an aerospike engine.

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eevilspock
What about the environmental impact? What are the wAste products of the
plastic solid fuel and oxidizer combustion?

