M
mrmorris
Guest
Except for the fact that they always have been -- why are current boosters generally designed 'tall and thin'? I ask this because I was recently pondering the Falcon I and thinking that if it were shorter and squatter, then less material would be required to enclose the same volume of propellant. I started to calculate it out, but had to make lots of assumptions since they didn't post engineering diagrams on their site for my convenience. Given my plethora of WAGs, however -- I worked out that increasing the diameter of Falcon I from 1.7 meters to 2.5 meters would reduce its height by ~8 meters and drop ~388 kg of aluminum required for the outer shells of the two stages. Since this is a significant fraction of the payload weight, it would seem that if this <b>could</b> be done, it <b>should</b> be done.<br /><br />Except nobody does it. Which leads me to think there's a significant engineering gotcha that I'm missing. My best guess is that it's flight stability. While having engines at the bottom is inherently unstable (hence Goddard's "engine at the top" rockets), the longer and thinner the rocket, the larger the percentage of thrust that runs through the center of mass and the less unstable it is.<br /><br />However, if this is the *only* reason, then it would seem to be an obsolete one. While the computer power that existed at the dawn of spaceflight might have been incapable of keeping larger-diameter boosters stable in flight -- that shouldn't be the case today. Given the current state of processing power -- if flight stability were the only issue, I would expect at least <b>somebody</b> to be experimenting with a boosters whose shape more closely approached a sphere (i.e. the minimum surface-area to volume ratio).<br /><br />So -- are there other reasons that I'm missing?<br />