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It looks like most rockets that head out of Earth, or even into orbit are pencil shaped (or nearly so). I would take this to mean there is some mass of air such vehicles push out of their way.

What alternative shapes may a rocket headed into space, or orbit have?

EDIT: This will probably seem crazy; I was toying with the idea of a tunnel or more extending some length of the body with some mechanism to pull the air out of the way forward and ejecting it backwards (sort of like a jet) to create a little bit of pressure differential. Sort of like striations on the body of a whale and other marines help it slip easily through water.

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Everything that's been tried is "basically" the same shape. Rockets are better if they're long and thin in order to keep the direction, and the tips are better if they are sharp to make them more aerodynamic and reduce the friction in the air. If you have some specific idea how the shape of a rocket could look like, could you please add it to the question? Otherwise the answer is that there's no other meaningful shape. –  Luboš Motl Nov 2 '12 at 20:00
It's funny that fish, if they move with any speed, all look like fish - small cross section, smooth, etc. Form follows function. –  Mike Dunlavey Nov 2 '12 at 22:13
@Mike Dunlavey: Cars were mostly horse-wagon shaped with a box saloon for quite a while after the first automobiles were produced... Then there was a paradigm shift when it became necessary to increase velocity –  Everyone Nov 3 '12 at 3:24
People have made some truly bizarre designs in Kerbal Space Program, though unfortunately it doesn't model aerodynamics properly yet. So most of the crazy designs would probably be unflyable in real life. So I guess you're stuck with build-it-yourself-and-see or learning how to use some computational fluid dynamics/finite element system. As others have said though the basic tradeoff is slim profile versus thrust (in atmospheric flight). In space shape really doesn't matter at all as long as the thrust axis goes through the centre of mass and you have enough torque for stability control. –  Michael Brown Jan 3 '13 at 8:35
You may want to visit the article on aerospikes: en.wikipedia.org/wiki/Drag-resistant_aerospike –  Deer Hunter Jul 9 '13 at 12:51

2 Answers 2

By definition, a rocket has to carry its own propellant (fuel + oxidizer) and so needs tanks to store it on the launchpad. Current large-thrust rocket technology (solid or liquid) has relatively poor energy to volume ratio (hello antimatter !) and thus the volume of these tanks are large. And so it's a double penalty at sea level where you have to carry all that weight under the strongest gravity field and you have this large volume that needs to fend through thick air. To mitigate this, and spend as little time as possible at low altitude with as little aerodynamic (both friction and pressure) losses as possible, there is like you said only one shape that really works.

Alternative solutions include launching from a plane at high altitude (Pegasus) but not so high yet that aerodynamics don't play a role: so the rocket still looks like ... a rocket. The issue here is that the plane cannot fly without air for lift and oxidizer and yet the rocket would like to be launched where there is no air. The ultimate solution to remove all aerodynamic constraint is of course the space elevator and the assembly of spacecrafts in orbit. But we're not there yet.

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I remember an ancient question: how many balls of string does it take to reach the moon. The answer of course was one, if the string was long enough.

This question has a similar answer. If you have enough energy, the rocket can be any shape you wish. Shape only affects the rocket in the atmosphere via friction. Beyond the atmosphere the shape does not matter for energy purposes.

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The shape of a rocket, while in space, does affect the energy needed to orientate whithin a certain amount of time, since the shape affects the moment of inertia. –  fibonatic Nov 7 '13 at 19:05

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