Liquid Fuel Engines
•Liquid Fuel is by far safer and can be switched off and on at will. Liquid fuel engines can also be fully throttled by controlling the amount of liquid fuel, oxidizer and pressure in the reaction chamber. •A scenario where liquid fuel is advantage over solid fuel is for a rocket flight or trajectory requiring multiple burns during the course of launch. Liquid fuel is ideal for dealing with what’s called Max-Q. •A disadvantage of liquid fuel is the refrigeration and time/complexity required to load and pressurize such volatile and dangerous fuels into a spacecraft prior to launch.
http://cdn.arstechnica.net/wp-content/uploads/2013/03/eande-f1-testfire.jpg
F1 Engine used on Apollo/Saturn V Rocket
Remember to explain MAX Q to the crowd. Metioned “Go for throttle UP”.
Talk about chill down of the fuel, lines and tanks and continual top off all the way up to launch.