From: root@mauve.demon.co.uk   
      
   Allen Meece  wrote:   
   > < 30* the speed.>>   
   >   Someone said that orbit would take 30 times the *energy* of a vertical   
   > flight to 100 km. Since then I've also heard *20* times the energy.   
   >   SS1 went Mach 3 on it's record flight and orbital speed is Mach 24. That   
   > means SS1 needs to go 8 times faster, to make orbit. The Mach 3 was achieved   
   > in vertical flight and the orbital speed will be done in mostly horizontal   
   > flight which takes less fuel.   
   >   I doubt it will take 8 times the fuel to go 8 times the speed. At 2 gee it   
   > should take 4 times the fuel to go 8 times the speed plus a little to boost   
   the   
   > extra fuel weight.   
   >   So that might require about 5 times at much fuel to obtain orbit?   
      
   Nope.   
   Taking this in order.   
   At 100Km, the potential energy of an object at rest is mass*gravity*height,   
   or about 1MJ/Kg.   
   To get to 8000m/s (orbital speed, neglecting drag) you need   
   1/2*mass*velocity^2 = 32MJ/Kg.   
   24^2/3^2 = 64 times the energy at mach 24, compared to mach 3.   
   Gravity is irrelevant, other than to make the trajectory less efficiant,   
   as you have to spend some fuel on avoiding hitting the atmosphere   
   at high speeds.   
   It takes the same amount of fuel to accellerate by a given amount   
   however fast you do it.   
   SS1 is (about) 40% fuel by mass.   
   So, increasing the fuel you need by 8 times will increase the mass   
   significantly.   
   Now, you have to run the fuel consumption numbers on the whole mass, so   
   it no longer looks quite so good.   
      
   Not to mention that you need a new carrier.   
      
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