h a l f b a k e r yClearly this is a metaphor for something.
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After reading Incremental Stage Rocket <link>, it occurs to me that "everybody knows" the people go on top of the rocket: There's the first stage, then the second stage, then the third stage, then an itty-bitty payload capsule right up top... why ?
Why not reorder the rocket ?
Instead of:
Payload
Big
Fuel Tank/Engine
Big Fuel Tank/Engine
Big Fuel Tank/Engine
have...
Fuel Tanks (plural)
Payload
Engine(s)
It's not like the astronauts need to see where they're going at liftoff anyways.
Incremental_20stage_20rocket
[FlyingToaster, Sep 13 2011]
Kerbal Space Program
https://kerbalspaceprogram.com/
Build rockets! [bungston, Oct 15 2014]
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Can you be more explicit about what the advantage would be? |
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It'd make the <link>ed concept work better: fuel tanks could just be tossed off the top along with their supporting structure, as opposed to the tank going but leaving the structure behind (until the entire stage gets released). |
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Less engine plumbing: you'd only need one set of pumps for all the engines (I'm assuming that multiple engines are required or at least multiple nozzle designs). |
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If there's an emergency while on the ground, it's easier to evacuate. (In the air they can be blown out the side instead of off the top.) |
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And astronauts with a fear of heights could avoid that scary gantry thing. |
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The emergency escape system on most rockets (space shuttle excluded) has a rocket above the capsule pulling it away from the rest of the rocket. So this is baked on a small scale. |
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I'm giving this a [-] though because if you applied that to the whole rocket you wouldn't be able to direct the thrust straight down, so you would lose some of your vertical lift component and it would be horrible inefficent. Plus how are you supposed to seperate stages safely? |
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If safety's a concern, then it would be better to have
an unmanned rocket connected, by a very long
bungee cord, to the crew capsule. |
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[DIYM] ... unbone me sir. I think you've misread the post. The payload section isn't nestled between the rocket motors. |
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The invention is for the rocket sections to be arranged as noted in the post: from top to bottom: fuel sections, then payload sections then engine sections. That way you could toss out fuel tank sections when they're empty if desired, or for that matter keep them if you want to bring them into orbit; likewise engines when they're past their working altitude. |
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There's distance between the fuel and engines, so if an engine blows up it doesn't automatically cause the fuel tank to explode. |
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//There's the first stage, then the second stage,[...]... why ?// |
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The Saturn V was designed by Werner von Braun, right? German dude, like those who included ballroom dancing in flight officer training in WWII? German engineer, to whom a bit of wasted complexity is no waste at all? |
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I think he would have answered your question with a question - "Well, did it work, or did it not work?" |
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[Lurch] Traditional multi-stage rockets work. So do BMWs (very nicely). But why don't we all drive BMWs? If cost is more important than the ultimate driving experience, you might want to look into something other than German engineering. |
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+ Interesting approach to saving the weight of extra engines that would otherwise be discarded half-way up. |
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I imagine you might want some of the engines mounted in a way that they can be discarded, but one engine in the middle would run the entire time. The mechanism to discard sections of the fuel tank from the top of the rocket while ensuring that they don't hit anything critical as they fall away seems like the biggest challenge. |
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Also: I'm not sure it's entirely logical, but somehow it seems more dangerous to be sandwiched between the engine and tons of fuel. |
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I think generally if there's an oopsy, it's not going to matter that much where you are... but in this case having, from the bottom: engine, engine, engine, payload, fuel... separates the engine (where the big flames are being generated) from the fuel tanks somewhat. |
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Tossing stuff off the top is more complicated. But there's also the option of carrying empty tanks into orbit for use as modules or something. |
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//ballroom dancing// At the start of the war, most of the flyboys were from the aristocracy. |
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It's rather convenient to drop off unnecessary weight as the rocket fuel stages are used up. Your version suffers from the side-effect of having to support all of that mass, high up, and then not being able to shed the supporting structure as fuel is expended. |
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BMW's suck for engineering, BTW. What they do have is good driving dynamics and lots of money for NVH absorbtion and cabin amenities. Anybody can throw money at a car and create a success. |
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What I was trying to say: the design team was entirely comfortable with trusting the technology and just stacking up as much as was necessary - with the shade of JFK pointing into the future, commanding "Fund that!" |
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I agree with the idea that the "build a stack of Legos" methodology is not the best possible way. We need, not a von Braun, but maybe a Kelly Johnson type chief designer. Without a congressional committee with funding erasers having direct access to make alterations to blueprints. |
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//not being able to shed the supporting structure as fuel is expended// Actually that's part of the plan too. |
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You (could) momentarily stop the engines between tanks and jettison both tank and frame relatively safely. |
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(of course what I really think is they should design rockets to be used as space station, habitat and interplanetary ship components: put it all up into orbit) |
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You wouldn't have a frame. The supporting structure, in an efficient design, would be mostly the rocket body itself. This rocket would be therefore overbuilt in order to support all of that weight at the top. |
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I'd think that rocket engines weigh much more than fuel tanks, volumetrically, ie: your argument works in favour of the post. |
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I thought we got to the stage that for reaching outer space
you don't need rockets anymore |
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I'm pretty sure the rocket surgeons have thought of
and rejected every other configuration in the
decades of rocketry performed by hundreds to
thousands of teams. Nevertheless, [+] |
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I think the main problems with this approach could be
discovered with a peek at the history of the S-IC, the first
stage of the Saturn V. |
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Notice that the first stage has oxygen tankage at the top
of the stage, kerosene at the bottom. Well, they didn't
want to put the oxygen at the top, because of the long
pipes. They also didn't want to put the kerosene at the
top because of the long pipes, and the kerosene being
more dense moved the center of gravity higher. Hence,
oxygen on top for lower COG. |
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You don't want to run the pipes for the liquid oxygen
*through* the kerosene
(a.k.a. "rocket propellent 1", or RP-1) because - well,
when you chill kerosene, you get a gelled waxy substance
which works exceedingly well at clogging holes - hence, it
won't work in engines. (A British Airways Boeing 777 came
to ground short of the runway at Heathrow a few years
back because of exactly this problem.) |
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But, if you wanted to run the oxygen suction lines
*around* the kerosene tank, there's a problem. The
reaction force of 3950 lbs/second of liquid oxygen turning
the corner in the pipe is greater than the tensile strength
of the tank material - the pipes would rip themselves out
of the bottom of the tank. Also, the change in direction
causes turbulent flow, which forms low-pressure eddies,
which can cause phase change unstability - the liquid
oxygen can explode into GOX, interrupting flow and
shutting down an engine. Also, the LOX trapped in the
lower portion of the of the tank is exposed to
environmental heating, which causes it to boil gently;
when the pressure exceeds the gravity load of the tank,
the pipe produces a "geyser" of comparatively warmer
(lower-density) LOX with GOX bubbles rushing up into the
oxygen tank, again resulting in an incompletely filled
suction line - this is most likely to happen after tank fill,
but before mass flow start: during countdown, leaving
that engine unable to start. |
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In the end, the Marshall and Boeing teams had to run the
five LOX suction lines straight from where they come out
of the bottom of the O2 tank directly to the engines. The
center engine fed with a line straight down through the
RP-1 tank, the other four with lines angled outward to
arrive directly at the engine mounts for the outboard
engines. Each one of these lines was contained in a large
insulated tunnel to keep from warming the LOX and
chilling the RP-1. Then, since the heat transfer was only
slowed, not prevented, the RP-1 was kept mixed by
bubbling nitrogen through it; liquid helium was injected
into the bottom of the LOX suction lines to keep them
from boiling. The liquid helium would boil to gas in the
oxygen, and rise up through the tubes, eventually
providing pressurization in the tank. |
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In your design, you're not going to have the simple
problem of getting the oxidizer through the fuel tank.
You'll need to get the first stage oxidizer AND fuel
through the second stage tankage, third stage tankage,
payload section, third stage engine rack, second stage
engine rack, and finally delivered to the engines at the
bottom. Then the shortened equivalent problem for
second and third stages respectively. |
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Unless, of course, you decide against staging, and go
SSTO - at which point, the problem you set out to solve
vanishes. (Replaced, of course, with a different set of
problems...) |
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Correct me if I'm wrong, but the different stage engines are different, because of the changing enviromental conditions they are working in (altitude, pressure, temperature, speed). External air pressure in particular is a big variable for rocket nozzle design.
That said, weirder designs like aerospike engines are meant to alleviate the pressure (not sure about the others) problem, so maybe you are on to something.
The "discarding used tanks" problem can be fixed by using 4 tanks per section (2 oxy, 2 fuel) which can be jettisoned symmetrically sideways (the way multiple booster rockets are these days).
Taking the "discard used tanks" to it's limit, you would be popping off tiny tanks continuously. So could you also use the tanks themselves as fuel/reaction mass? Or a "stored as solid, melted to use" combined fuel/oxidiser that doesn't need a tank (maybe a thermal coating for high speeds...)?
Could you make a solid-fueled rocket (using atmospheric oxygen) that is just fuel?
So many questions! I need a rocket scientist, stat! |
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//solid rocket-fuel (with atmospheric oxygen)// "Piston Rocket", in the same category, might be a starting point, though I think what you're looking for would more viably be termed a "solid-fuel jet". |
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I'm currently just annoyed that in the interest of convenience they toss away perfectly good structural components andor raw material that could be used to build more stations or other things in orbit, while creating new knowledge and experience, ie: how to build things in space. Restacking the rockets - combining all the fuel tanks together - would mean that only the engines get tossed. |
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The Kerbal space program would allow you to test this. That would do for the center of mass question. |
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