Why ion propulsion?

What is the difference between an ion engine and a conventional one?

Both kinds of rockets move the ship forward by making thrust. This thrust is made by propelling matter out of the back of the ship. Ion engines are different from chemical engines (engines that work by burning liquid or solid fuel) in where they get their energy and how they produce thrust.

Chemical engines work by combining fuel with an oxidizer. That makes a gas that expands and rushes out the back of the engine, making thrust. Chemical engines are mass-limited engines. What this means is that how much power a chemical engine has depends on is how much fuel and oxidizer the rocket can carry. When the propellant runs out then the rocket cannot go any faster.

However, ion engines work differently than chemical engines. Ion engines take very small amounts of gas and accelerate it to very high speeds, unlike chemical engines which take large amounts of gas and spew it out at a slow speed. This means that an ion engine uses a lot less fuel. Ion engines are limited by energy, not by mass. Therefore "running out of gas" is not a large problem with ion engines. The limit for ion engines is usually where to get all the electricity to feed the ion engine. Ion engines are limited by how much energy (electricity) that a rocket can carry or how much energy the solar panels can collect.

What is a propellant?
Why does DS1 have two types of propulsion?
How does DS1's engine work?
Could NASA use ion propulsion to put a ship into space?
How do conventional rockets work?
Where does DS1 get its electricity?

What are the types of rocket propulsion?
Why is mass important?
What is thrust?
What is a propellant?