Payload mass is the mass of the payload carried by the craft. In a multistage spacecraft the payload mass of the last stage is the mass of the payload and the payload masses of the other stages are considered to be the gross masses of the next stages. For a rocket stage, the payload mass is usually close to the empty mass. A Saturn V class rocket has a typical payload mass of 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, payload mass is calculated which is in turn used to calculate final velocity, fuel flow 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
payload mass = fixed payload + tank mass * payload ratio

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

In atmospheric spacecraft, multi stage spacecraft, and spacecraft cost given empty mass and payload ratio, payload mass is calculated which is in turn used to calculate orbital payload.

payload mass = payload ratio * empty mass

orbital payload = fuel * empty mass + payload mass
 
 

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