Oxidizer density is the density of the oxidizer, commonly expressed in kilograms per cubic meter. The greater the oxidizer density, the greater the amount of oxidizer that can be stored in a given tank and the greater the mass of oxidizer than can be pumped for a given pump. Oxidizer density generally increases with increasing molecular weight of the oxidizer molecules. Oxidizer density also generally increases with increasing molecular weight of the component atoms of the oxidizer molecules.

All else being equal, an increase in density increases the overall performance of rockets, especially pressure fed ones, because tanks are heavy compared to pumps. Hydrogen peroxide has the highest density and molecular weight of any oxidizer in common use. Oxidizer density is used to calculate oxidizer volume ratio, which is in turn used to calculate the tank mass.

oxidizer volume ratio = oxidizer mass ratio / oxidizer density

tank mass = tank pressure * 3.0 / effective tensile * ( fuel volume ratio + oxidizer volume ratio + propellant volume ratio )
 
 

This is used in astropolis, pumped rocket and rocket cost.
 
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