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In message - Bradford Liedel
writes: I find this stuff very interesting. I'm curious to see if (within the next 30 years) space travel actually becomes a consumer industry rather than a government only industry. With backstreet boys being launched into space, towers into the atmosphere, corporations competing on new shuttle designs, etc...who knows what this will all bring. I often see this type of thinking: "if only we'll start launching on commercial scale things will be cheap". Well, things are not that rosy: physical limits come to play. The classical rocket equation: dv = Ve * ln((final mass) / (initial mass)) whe Ve = exhaust velocity. dv = change in velocity The exaust velocity is more or less constant for chemical fuels. In F-1 engines of the Saturn-V first stage it was around 2.9 km/Sec in vacuum (2.6 km/Sec at sea level). The required dv is about 8 km/Sec (to LEO). Substitute the figures into the equation and you'll get that final mass is only about 5% of the initial mass. That means: 95% of the rocket mass is fuel and the WHOLE structure and payload and engines has the meager 5% of the mass budget. That'll dictate you engineering decisions very uncomfortable to live with: 1) You can't make the spacecraft "sturdy as a buttleship", in fact you'll be forced to make its structure rather flimsy (forget about "belly landing" with shuttle) and therefore you'll have to very thoroughly inspect it before EVERY flight to make sure absolutely nothing is damaged and probability of slight damage requiring repairs will be quite high. Such inspection by an army of technitians adds cost. 2) The cryogenic fuels (LH2+LOX or Kerosine+LOX or other similar stuff) are much mode dangerous to handle than ordinary jet fuel, therefore in almost any event of unexpected pre-launch maintenance you'll need to drain the tanks and refill them again and it's not as simple as dealing with jet fuel - again you'll need many more people which again adds to the cost. 3) Because of the tight mass budjet (5%) every equipment must be on the cutting edge in terms of mass (materials used) which makes it expensive to build and maintain. I'm not saying you can't make launches cheaper than NASA does (if Shuttle launch costs $19,000/kg and is equal to Saturn-V launch cost per kg than clearly NASA missed something implementing the "reusable cheaper than expandable" attitude) but there are inherent technical problems which can't be solved in a cheap way when you'rr constrained by the 5% mass budget. However, if you'll use nuclear propultion - that really opens the road to cheap space access. All you need is LOTS of R&D money to restart programs USAF conducted in 50-s and 60-s (and got as far as having working prototype of nuclear rocket on a test stand) and solve the problems of engine life, radioactive exhaust, worst case launch failure survivability of the reactor, etc. And of corse, you'll need to re-educate the public (voters) to allow polititians to make such decisions. ************************************************** **************************** * Arie Kazachin, Israel, e-mail: * ************************************************** **************************** NOTE: before replying, leave only letters in my domain-name. Sorry, SPAM trap. ___ .__/ | | O / _/ / | | I HAVE NOWHERE ELSE TO GO !!! | | | | | | | /O\ | _ \_______[|(.)|]_______/ | * / \ o ++ O ++ o | | | | | \ \_) \ | \ | \ | \ | \ | \ | \ | \_| |
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