Rockets that need higher energy propellants and controllability (throttling or restart capability) often choose liquid propellants. Generally speaking, liquid propellant combinations has higher energy levels (specific impulse) than solid propellant mixtures.

What are liquid propellant rocket used for?

Liquid rocket engines are used on the Space Shuttle to place humans in orbit, on many un-manned missiles to place satellites in orbit, and on several high speed research aircraft following World War II.

What are 2 advantages of liquid rocket fuel?

Advantages of liquid propellant rockets include the highest energy per unit of fuel mass, variable thrust, and a restart capability. Raw materials, such as oxygen and hydrogen are in abundant supply and a relatively easy to manufacture.