Comment Wrong! (Score 2, Informative) 283
I do not know what kind of efficiency you mean, but in terms of energy efficiency rockets are actually very good. A rocket engine transforms about 90% of the chemical energy of the propellants to kinetic energy. This is excellent.
The total energy efficiency of an orbital rocket can be defined as the potential energy of the empty rocket in orbit divided by the chemical energy in the propellants. Even here rockets are not that bad.
If you have a hydrogen powered rocket with a specific impulse of 4300m/s and a total delta-v of 9000m/s, your mass ratio is 8.109, so the propellant weighs 7.109 times as much as the empty rocket. But the empty rocket has a specific kinetic energy of about 30 MJ/kg, whereas the propellants only have a specific chemical energy of 11MJ/kg. The total efficiency is thus 30/(7.109*11)=0.38. Not too bad, eh?
The reason rockets are still so expensive is that most current rockets are direct descendants of ballistic missiles where cost was not important. And the shuttle is a f***ing joke.
regards,
tuttle
The total energy efficiency of an orbital rocket can be defined as the potential energy of the empty rocket in orbit divided by the chemical energy in the propellants. Even here rockets are not that bad.
If you have a hydrogen powered rocket with a specific impulse of 4300m/s and a total delta-v of 9000m/s, your mass ratio is 8.109, so the propellant weighs 7.109 times as much as the empty rocket. But the empty rocket has a specific kinetic energy of about 30 MJ/kg, whereas the propellants only have a specific chemical energy of 11MJ/kg. The total efficiency is thus 30/(7.109*11)=0.38. Not too bad, eh?
The reason rockets are still so expensive is that most current rockets are direct descendants of ballistic missiles where cost was not important. And the shuttle is a f***ing joke.
regards,
tuttle
