Specific impulse

Our topic for today is another rocketry concept: Specific impulse (usually abbreviated I_sp).  Basically, it's how efficient your rocket engine is.  It's defined by how far each unit of fuel moves your rocket.
Here's the formula:
  Where:

• is the specific impulse in meters per second
• the thrust in newtons
• the fuel consumption in kg/s

So, Isp is how much thrust you get per unit of fuel.

If your Isp is higher, then you can get more Delta-V with the same rocket.  In the rocket equation,  is used instead of Isp, but the concepts are the same.