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Space Forum / Shuttle / October 2005Magnetic levitation for launch ?
People have discussed "thethers" which have to have heights in the tens of thousands of kilometres. What about a tower of a scale of WTC or CN Tower or even twice that with extremely powerful magnetic linear engines. Stick the shuttle against it with the right aparatus, and use that tower to help launch the shuttle. Wouldn't such a system impart a large amount of upward energy to the shuttle and thus greatly reduce the need for fuel, thus allowing a smaller ET (and thus lighter vehicle) ? (replace shuttle with CEV or whatever). In other words, instead of a full tether, why not a much smaller structure that imparts a huge force to provide the initial acceleration , thus reducing the need to carry as much fuel ? John Doe <jdoe@doe.org> wrote: >In other words, instead of a full tether, why not a much smaller >structure that imparts a huge force to provide the initial acceleration >, thus reducing the need to carry as much fuel ? For the same reasons that every gun/catapult/maglev proposal since Jules Verne has been D.O.A. If the launch device is long enough to provide a useful fraction of the delta-v needed for orbit without ungodly G forces, it's too expensive to build. If your vehicle exits the launch device fast enough (even at Everest altitude) to coast to orbit, it's fast enough to burn up and/or break up almost instantly. And if you get around those two by launching a vehicle that then accelerates with its own engines and propellant, as in your suggestion, the math says you'd be better off either air-launching from the largest carrier plane available, or just using a bigger rocket in the first place. > People have discussed "thethers" which have to have heights in the tens > of thousands of kilometres. [quoted text clipped - 8 lines] > shuttle and thus greatly reduce the need for fuel, thus allowing a > smaller ET (and thus lighter vehicle) ? That's an interesting idea. Theoretically, given a tower of 1500 ft, a 3g acceleration would yield an extra 300 mph, 5g's would yield a little over 400 mph, and 9 g's would yield about 600 mph. Of course this would require a much strong vehicle. <snip> George Evans > People have discussed "thethers" which have to have heights in the tens > of thousands of kilometres. [quoted text clipped - 14 lines] > structure that imparts a huge force to provide the initial acceleration > , thus reducing the need to carry as much fuel ? Uh, wouldn't the specific impulse needed for something like this be so great it would pretty much result in the rocket falling apart? Mag-Lev only makes sense if it's over a longer distance, where you can build up the acceration slowly enough to not kill your passengers or destroy your craft. > Uh, wouldn't the specific impulse needed for something like this be so > great it would pretty much result in the rocket falling apart? No different than powerful rocket engines. At liftoff, you ghave a huge mass and acceleration isn't the problem because the thrust to weight ratio is low. The idea of the "catapult" was not to fully launch the vehicle, but just assist its launch to reduce the fuel needed and thus allow more payload (or reduce overall size). what may go is a wind tunnel cannon designed to get a scram jet operating *before* the vehicle leaves the ground, perhaps a "jet" or "rocket" whose exhaust gases could be used to get the ramjet *scramming* either before takeoff or just before and after kinda like a long tube full of propellant that the little scramjet has to traverse - piling up a shock as it goes - the velocity does not have to be hypersonic either to get the thing scramming as the propellant mix is confined and can be "pre-compressed" via a shock wave coming down the barrel, induced by sound or explosion... hmmmm a scram jet cannon -> a scramnon? a scrammon!!! > People have discussed "thethers" which have to have heights in the tens > of thousands of kilometres. [quoted text clipped - 14 lines] > structure that imparts a huge force to provide the initial acceleration > , thus reducing the need to carry as much fuel ? Another small detail overlooked in this discussion is Newton's Law of Reaction. Mag-Lev launches in a tangential direction, as in trains, cancel out; that is, the trip going cancels the reaction of the trip coming. Such would not be the case in vertical launches. As the number of launches rise, the destabilizing effect on the Earth's rotation and/or orbit would soon be felt. Who would accept a changing period for a year or day as a fair exchange for saving a few loads of rocket fuel? > People have discussed "thethers" which have to have heights in the tens > of thousands of kilometres. I think you are referring to something called a "space elevator". Just a concept right now, but an interesting one. Google on the term "space elevator". JD |
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