How does density affect tank volume?
Density is the amount of space that a certain mass of material takes up. A dense material such as water is heavier than a less dense material such as gasoline for a certain size. A rocket which needs a certain mass of a fuel can use a smaller tank of a denser fuel rather than a bigger tank of a less dense fuel. The smaller tank will cost less to construct and be lighter than the large tank. However, there is a tradeoff by using a denser fuel like RP-1 or UDMH because they are lower performance fuels then LiH which produces a higher specific impulse.
