There are several limitations on the ability to expand a launch vehicle past certain sizes. One of them is tank diameter. On the smaller launchers, diameter limits might be dictated by available pipe sizes. A step up from there and tank diameter might be limited by available tooling. A couple of steps up from there and ground transport becomes an issue. Too large and it becomes somewhere between inconvenient and prohibitively expensive to transport from factory to launch site. Another limitation is height and fineness ratio. A launch vehicle gets into problems when the stack length is too large a multiple of tank diameter. 8″ irrigation tubing might be a good basis for a 10′ rocket, but gets into trouble before it reaches 20′. By the same token, the Atlases, Falcons, and similar vehicles are probably very close to the limits of length in relation to diameter. The standard build for a launch vehicle is, starting from the bottom, engines, fuel tank, inter tank structure or common bulkhead, LO2 tank, inter stage adapter, engine, fuel tank, inter tank structure or common bulkhead, LO2 tank, and payload. This is all in one long skinny cylinder except for a hammerhead shroud. To make the launch vehicle larger requires either more diameter, more length, or both, with the manufacturing and transport problems from the diameter increase, or the structural problems from the length increase. There might be a way to double the size of a given vehicle class while holding the costs and other problems down. This idea is to build a vehicle that is asymmetrical around existing tooling. Also use a modular assembly technique to avoid both transport problems and the necessity of new tooling or construction techniques. I still don’t have a computer that lets me draw cartoons all that well. The sketch is two possibilities for the vehicle concept. A stretched LOX tank built on existing tooling that is as long as the original entire first stage. A stretched Kerosene tank proportionate to the LOX tank also built on existing tooling. These tanks are trucked separately to the launch site where they are clamped together along with the thrust structure. On the left the sketch has the helium tanks, avionics and such in the space above the shorter Kerosene tank with the second stage above the center line of the vehicle. The figure on the right has the second stage nested above the Kerosene tank with the helium tanks and such moved elsewhere. If this concept is feasible, a first stage could effectively double in size without causing problems in manufacturing and ground transport. Engines would double in number, but dome tank ends would not. The increased cost of the larger vehicle would be dominated by the engines. Eliminating the inter tank structures would eliminate a place for fumes to gather and possibly cause problems. The tank connectors could easily be lighter and cheaper than the normal inter tank structure. There would be no place at all for potentially explosive fumes to gather, which means that a leaking tank might be less of a problem. By going modular, any problem section could be swapped out with relatively little effort. The four modules being LOX tank, Fuel tank, thrust structure, and second stage. Two of these units could be flown together in a quad layout. Three of these units could act as boosters/first stage for a conventional vehicle centered between them in the seven tank hexagon layout.
Latest posts by johnhare (see all)
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