Empty mass is defined as the mass of the spacecraft without fuel or payload. This is usually about a tenth of the mass of the spacecraft. The heaviest components of a spacecraft are the tanks, the easiest way to minimize their mass is to use pumps to boost the pressure of the liquids entering the combustion chamber. The empty mass of a Saturn V class craft is two hundred and fifty thousand kilograms.

In pumped rocket and rocket cost given effective tensile, engine mass, fuel volume ratio, interface mass, mass, oxidizer volume ratio, payload ratio, propellant volume ratio and tank pressure, empty mass can be calculated which is in turn used to calculate empty mass ratio, empty falling speed, initial hours and structure cost.

fixed mass = engine mass + interface mass
fixed payload = payload ratio * fixed mass
relative tank mass = fuel volume ratio + oxidizer volume ratio + propellant volume ratio * tank pressure * 3.0 / effective tensile
tank payload = relative tank mass * ( 1.0 + payload ratio )
remaining mass = mass - fixed mass - fixed payload
fuel mass = remaining mass / ( 1.0 + tank payload )
tank mass = relative tank mass * fuel mass
empty mass = fixed mass + tank mass
 

empty mass ratio = ( mass - payload mass ) / empty mass

empty falling speed = sqrt( empty mass * 9.8 m / s^2 / drag )

initial hours = ten ton craft work * pow( ( empty mass / 10,000 ), labor scale factor )

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 atmospheric spacecraft, multi stage spacecraft and spacecraft cost given mass and empty mass ratio, empty mass can be calculated which is in turn used to calculate initial structure, launch hours and payload mass.

empty mass = mass / empty mass ratio

initial structure = structure price multiplier * ten ton structure price * pow( ( empty mass / 10000 ), structure mass scale ) * pow( ( exhaust velocity / 3330 ), structure exhaust scale )

launch hours = pow( ( empty mass / 10000 ), labor scale factor ) * ten ton craft work

payload mass = payload ratio * empty mass
 
 

Feedback   Free Electronic Nation Home    Rocket   Spacecraft   GNU Free Documentation License