037dbc1c   
   From: AKWolffan@gmail.com   
      
   On 2017 May 20, trident wrote   
   (in article<08ca389c-116b-48f2-8128-967cf4c47dd3@googlegroups.com>):   
      
   > I figured that ethanol is the cheapest fuel with going as low as 1 cent per   
   > kg. But what about oxidizer? Liquid oxygen can go as low as 66 dollars per   
   > tonne but is the best price one can get, taking into consideration Isp   
   > differences?   
      
   you need to define your terms. ‘Cheap’ in what way? Cheapest for high   
   specific impulse? Cheapest for high thrust? Cheapest by mass? Cheapest by   
   volume? Are you going with just chemical systems, or are electrical or   
   nuclear allowed to play?   
      
   Hint: ethanol is a very bad chemical fuel. High mass, low density, poor   
   specific impulse. Liquid hydrogen, kerosine, and gasoline are all far better.   
   Yes, it’s cheap by mass, but you need a _lot_ of it because of its low   
   specific impulse. Your mass ratio is going to suck. And its low density means   
   that the tanks to hold it are going to be large. It might cost less per kilo,   
   but given the number of kilos you’ll need plus the mass of tankage to hold   
   all those kilos, ethanol would cost more than, say, kerosine. Worse, burning   
   ethanol simply doesn’t generate all that much thrust, so you’ll have a   
   problem getting sufficient thrust to get off the ground if you build a rocket   
   which carries enough ethanol fuel to run a significant mission.   
      
   remember always: deltavee = veesube * MR, where deltavee is your total   
   mission change in velocity, veesube is the exhaust velocity your rocket puts   
   out, and MR is your mass ratio, the ratio between the mass of rocket plus   
   consumables at the start of the mission to the mass of whatever’s left at   
   the end. worse, your thrust is dependent on the veesube _and_ your fuel flow   
   rate. Unless your veesube is very, very, VERY high indeed, having a low MR   
   and therefore a low fuel flow rate (you can’t have a _high_ rate if you   
   just don’t have the fuel, now can you?) means that you’re going to have a   
   low thrust. Ion systems and nuclear hot jets of the NERVA type have nice high   
   veesubes and nice low MRs... and low thrust. Ethanol would give low veesube,   
   high MR... and, because of the low veesube, low thrust.   
      
   There would be a _reason_ why serious liquid-fueled rockets use kerosine, or   
   hydrogen with liquid oxygen for oxidizer, or hydrazine and nitric, or pretty   
   much anything except ethanol. Some rockets used a mix of hydrazine and   
   methanol; see further C-Stoff and the Me-163. So far as I know no-one used   
   ethanol, either pure or in a mix. It should be noted that C-Stoff was   
   notoriously highly troublesome to handle.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)