What's the difference between reaction mass and fuel?

Question

I read an article on space travel that said you need to factor in reaction mass AND fuel. Are these not the same thing?

Answer 1

Hi. Earl D is correct. The ion engine is a good example. It uses electric fields to cause xenon gas to be pushed in one direction while the engine (and any attached ship) moves in the opposite direction. Xenon is the reaction mass, the fuel is whatever makes the electric field. http://www.answers.com/main/ntquery?s=ion+engine&gwp=13 In a chemical rocket the fuel and reaction mass are one and the same.

Answer 2

Fuel is what makes it have an action, which is what causes a reaction. Fuel has mass. The action (and resulting reaction) must have more than enough action to move the mass.

Action is backwards energy or thrust caused by the fuel. It must have enough reaction (momentum, causing movement in the opposite direction from the energy action) to move the mass of fuel.

You have gravity which is an attraction on the mass (fuel) pulling it downward. You have energy action (burning of the fuel towards the ground) this must be strong enough to move the fuel upwards (countering gravity).

If gravity is 7 feet of travel per second downwards and energey action is only 6 feet per second you will not move upwards. For this to happen the energy must be 7.1 feet or more of upwards motion to counter the pull downwards.