h a l f b a k e r yI CAN HAZ CROISSANTZ?
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The V2, the great granddaddy of all rockets, was designed as a ballistic missile, its mission to skirt outer space just above the Karman line (62mi) and, in a controlled fashion, reenter the atmosphere and hit a ground target headfirst, unpowered. An arrowlike design accomplished the mission rather
successfully, minimizing air drag and maximising control, both while balancing on a single-nozzle rocket engine during ascent, and during unpowered descent.
Today's space missions have a completely different operational paradigm: they go up 200-400 miles and don't come back down. Very little of the journey is spent in the atmosphere where radical streamlining is a must. And the payload isn't limited to a relatively small amount of high-explosives, or even a few hairless monkeys up for a bit of sightseeing.
Posited is that lofting a rocket high enough by whatever means available: balloon, jet engines of various configurations, perhaps assisted by low-thrust rockets, is a viable workaround for the low-altitude atmospheric drag that otherwise necessitates pencils with fins stuck on the end.
The idea then is short fat rockets, the various sets of engines mounted in a ring(s) at the bottom, from which they can be dropped (if wanted) when they're done, along with empty fuel tanks.
The purpose of course is to be able to make use of the simple mathematics of volume vs surface area: a sphere, indeed any shape where all the dimensionsal measurements are similar, requires less material, ie: weight, than a skinny tin can, or series of skinny tin cans thereof, for the same internal volume.
Space stations, large satellites, moonbase buildings, can all be lofted up in one piece.
While we're at it, let's change the term "microgravity" to "paraweightlessness".
Starbug?
http://www.fotothin...dd1d75e544d3a38cf7/
[bhumphrys, Feb 12 2014]
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I don't get this, I'm afraid. |
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The point about using aircraft or balloons for the
ascent through most of the atmosphere is fine,
and works very nicely for small rockets especially
(since they are especially penalized by air
resistance). For much bigger rockets, it turns out
to be cheaper and easier to use rockets all the
way. |
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But then there's your argument about surface area
versus volume. Yes, a sphere encloses more
space than a cylinder of the same surface area,
but why is that such a big advantage? |
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What matters most (air resistance aside) is
enclosed volume per unit weight. That value will
be somewhat bigger for a sphere than for a
cylinder, but not hugely so. |
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I'm also not convinced that having the thrusters
placed around a ring at the base is an advantage.
It's a misconception that a rocket with a central
thruster "balances" on the thrust. What matters is
that the thrust _line_ (which will run through the
axis of a single rocket, or through the overall
centre of a series of rockets arranged in a ring)
should be co-axial with the rocket for straight
flight. |
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Indeed, having multiple thrusters around the
periphery of a fat rocket is a recipe for disaster, as
any difference in power between the thrusters
will tilt their thrust line. Not so for a single
central thruster. |
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I didn't claim it would be cheaper: even though the structure would be lighter all'round, you'd use up a fair amount of juice getting up to the point where aerodynamics is a non-sequitur. (Hopefully using exotic jet-engines would mitigate that a bit) |
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But the point is to allow for large objects to be transported without requiring they be assembled in space. Even sticking with cylinders, having one twice as wide means it can be 4x shorter for the same volume. Or can hold 4x as much for the same length. |
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re: rocket placement, I think modern computers would be up to the task of load-balancing. |
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Ah, right, well then maybe. But I think the main
problem of transporting large objects into space is
more one of mass than of largeness. Still, carry on. |
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Seems a good match for a weather balloons supported launch pad. If you get your cartoonish rocket out of the atmosphere mostly before you lift off, the aerodynamics will have lot less impact. Be nice if you could reuse the launch floating pad. Hindenburg. |
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Get good radios cause your likely to drift a long way before countdown. |
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A four slice toaster might be a good model as to rocket shape. The LEM was not hampered by a lot of aerodynamic design cause the cheese has no atmosphere. |
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Picture say a 2:1 ratio of height to width, shaped like a lead bullet, possibly with a boat-tail. |
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The engines aren't placed around the outside: they're arranged probably about 2/3 the way out from the middle, wherever the load will be equal on the inside and outside of the engines' thrustlines. |
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FT suggested launching above the thickest part of the atmosphere, so as to avoid the aerodynamic limitations of the chubby rocket. If that’s the way you want to go, my I suggest modifying a cloud 9 as a launch pad. |
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The aerodynamics of a well designed chubby rocket are not as bad as people seem to be supposing. First the Satin 5 rocket is not a very aerodynamically sophisticated design, with its long strait parallel sides, it relied on brute power to get where it was going. Long strait sides produce a type of aerodynamic drag called surface drag. Surface drag can be minimize by traveling at a set cursing speed, but rockets are designed to accelerate. |
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Nature as had a lot of practice at coming up with shapes tat have to pass through the air at speed, and all of natures examples are fatter in the middle, with curved sides. |
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It is just a guess but I would suppose that the best shape for a single stage rocket would be; 1.5 times as long as I is fat, with its fattest point just below half way down, and a continuously chaining radius of curvature. AN EGG! |
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//Surface drag can be minimize by traveling at a set
cursing speed// Not so - I tend to curse most when
I'm in stop-start traffic. |
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It's a mystery to me why rockets aren't shaped like
footballs or boxerfish. |
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I think it's the G-forces; stuff not right above the thrustline has to be braced more to keep it from falling apart sideways. Solved in this idea by having rings of engines as opposed to a single centerline thrust. |
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It decouples the need to be aerodynamic for the
first 5 minutes of it's life, compared to zero need to
be aerodynamic for the next 20 years, when it's
doing its work. |
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It also has the added benefit of "why so fast"? |
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If you use rockets in the lower atmosphere, you
must go fast or else you waste too much fuel just to
hover. |
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But, if you use balloons for the lower atmosphere
part, you can take all the time you want/need, &
spend so much less energy. |
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