Pump density scale is the rate at which the cost of the pump changes relative to the rate at which the pump power density changes. A value of zero means that the pump cost is independant of the pump power density, higher values mean that the pump becomes more expensive as the pump power density increases. The baseline power density is one hundred and sixty thousand watts per kilogram, which is the power density of the space shuttle main engine turbopumps.

The pump power density can be increased by opening up its design, operating the pump at higher temperatures, operating its components at higher tip speeds, testing many designs and using light materials like ceramics. Operating a pump at a higher power tends to reduce its service life and decrease its reliability, increasing its effective cost. The pump density scale is used along with the pump power, pump power density, structure mass and ten megawatt price to calculate the pump cost.

pump cost = pow( ( pump power density / 160,000 ), pump density scale ) * pow( ( pump power / 10,000,000 ), structure mass scale ) * ten megawatt price
 
 

This is used in rocket cost.
 
 

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