While fire itself may not have mass or density, the materials involved in the fire (fuel and oxygen) do have density.
In the context of a rocket engine, the combustion process involves the ejection of high-speed exhaust gases, which have mass and therefore contribute to the overall density of the vehicle.
While fire itself may not have mass or density, the materials involved in the fire (fuel and oxygen) do have density.
In the context of a rocket engine, the combustion process involves the ejection of high-speed exhaust gases, which have mass and therefore contribute to the overall density of the vehicle.