eder@ssc-vax.UUCP (Dani Eder) (11/28/84)
> There were two estimates of the acceleration necessary for an EM launcher > to work: 92 g and 1000 g. I'm not going to argue which is right since > I can't think of subjecting any object to those forces except raw materials. > To manufacture something which could take that kind of acceleration would > either cost too much or add weight to the object just to strenghthen it. > Sending only raw materials into space would solve this problem (manufacture > what you need in space). I still don't know what kind of vehicle (to put > the raw materials into) could withstand the forces. Seems like the vehicle > itself would account for the lions share of the launch weight. Take type 7075 Aluminum as an example. It has a yield strength of 73000 psi, and a density of .1 lb/cu in. Thus a column 730000 inches high would give way under its own weight (at 1 g). Similarly, a column 730 inches high would give way under 1000 g acceleration. If you back off by a factor of 10 in acceleration, then the aluminum could support 9 times its weight in other stuff, plus its own weight. In the real world, you back off from the yield strength to have a margin of safety, and there are materials considerably stronger per weight than aluminum. But the general message is at 100 g's the structural weight is a small fraction of the total, if the object is 60 feet long. At 1000 g's, the object would have to be on the order of 6 feet long for the same result. I'll list the figures for the 92g projectile: Total mass 30 000 kg Payload 5102 Oxidizer 14871 Fuel 4957 Vehicle 5070 Structure 1373 Oxidizer Tank 771 Fuel Tank 217 Body Shell 285 Payload Adapter 50 Thrust Structure 50 Thermal Protection 280 Electronics 276 Power 238 Propulsion 1040 Main Engine 500 Plumbing/Pressurization 340 Steering 50 Nozzle Extension 150 Auxiliary Propulsion 600 Recovery System 228 Payload fairing 385 Growth Margin 650 As for what the payload could be, 75% of the payload brought to low earth orbit is propellants. Fuel doesn't particularly care how many g's it sees. Rolls of aluminum for a Grumman-type beam builder can stand high g's. Solid state electronics, if packaged properly, can also withstand high g's. But even sticking to propellants and structural parts, you have accounted for the vast majority of payload weight to orbit. Dani Eder / Boeing Aerospace Company / ssc-vax!eder / (206)773-4545