How does propulsion work?

Why does DS1 have two types of propulsion?

DS1 carries two different propulsion systems:

DS1 systems serve different purposes. The ion propulsion engine serves to push DS1 forward more quickly so that DS1 can get to where it needs to go in time to meet the objects in space it is supposed to meet. The hydrazine thrusters are used to control the spacecraft's attitude (the direction it is pointing in 3 dimensions). Once the spacecraft is pointed in a different direction, the main thruster can push it in that new direction.

DS1 cannot do both jobs with one kind of thruster. It is not possible to change the direction of the Solar Ion Propulsion thrust so it cannot be used for changing the ship's attitude. The hydrazine thrusters are not strong enough to be the main thruster. They will not increase DS1's speed enough to get it to where it is going.

How did DS1 get into space?
How does DS1's ion engine work?
How does solar electric propulsion (ion propulsion) work?
Why ion Propulsion?
How do scientists know what the path of an object in space will be?
How do objects in space travel?

What is attitude control?
What kind of fuel do DS1's attitude thrusters use, and how much of it do they use?
How fast does DS1 go?

What is hydrazine?