The structure exhaust scale is the rate at which the cost of the structure changes relative to the rate at which the exhaust velocity changes. A value of zero means that the structure cost is independant of the exhaust velocity, higher values mean that the structure becomes more expensive as the exhaust velocity increases.

Higher exhaust velocities generally cost more, partly because the rocket engines have to run hotter and partly because the fuel tanks have to made of more expensive materials and have more insulation to contain colder propellants, which have higher exhaust velocities. The baseline exhaust velocity is three thousand three hundred and thirty meters per second, which is the value for an engine burning oxygen and kerosene.

In rocket cost the structure exhaust scale is used along with empty mass, exhaust velocity, structure mass scale, structure tensile scale, tensile energy and ten ton structure price to calculate the structure cost.

structure cost = pow( ( empty mass / 10,000 ), structure mass scale ) * pow( ( tensile energy / 205,000 ), structure tensile scale ) * pow( ( exhaust velocity / 3,330 ), structure exhaust scale ) * ten ton structure price
 

In spacecraft cost the structure exhaust scale is used along with the empty mass, exhaust velocity, structure price multiplier, structure mass scale and ten ton structure price to calculate the initial structure cost.

initial structure = structure price multiplier * ten ton structure price * pow( ( empty mass / 10,000 ), structure mass scale ) * pow( ( exhaust velocity / 3,330 ), structure exhaust scale )
 
 

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