The chemical energy of the propellants (liquid hydrogen and oxygen) is given by chemical reaction theory. Since one mole of hydrogen reacting with oxygen generates about 68 kcal of energy, which is 286 kJ, the energy per mass of hydrogen is 143 MJ/kg. For a typical launch vehicle, the payload mass in GEO is approximately 1% of the initial mass of the launch vehicle, and about 80% of the initial mass of the vehicle is for the propellants, whose fuel fraction is 1/7. The mass of liquid hydrogen required for launching 1 kg of payload into GEO is taken to be about 10kg. Thus, the chemical energy to be consumed in putting a unit mass of payload (SPS) into GEO is estimated to be 1430 MJ/kg. The production energy for propellants is based on Mann’s study [7], According to his study, the electrical energy required for the production of hydrogen gas is about 120 kWh/lOOOscf, that is, 192 MJ/kg. In addition to this energy, 2.5 to 3 kWh of electrical energy are required to get a liter of liquid hydrogen, which corresponds to 128-154 MJ/kg. Thus the total energy required for the production of liquid hydrogen is about 350 MJ/kg. The energy cost for production of liquid oxygen is one order of magnitude lower than that for the production of liquid hydrogen and so is ignored in this study. So, the production energy of propellants per unit mass of SPS is about 3500 MJ/kg. Current launch vehicles are designed to carry expensive spacecraft completely assembled on Earth. On the other hand, space vehicles which will carry SPS to orbit can be more appropriately compared to ocean-going vehicles than to missiles. So, the industry to build cargo launch vehicles is considered to resemble the shipbuilding and automobile industries, and the energy cost will be better reflected by the industrial statistics of the existing mechanical engineering industry.
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