## Wednesday, September 2, 2015

### Specific impulse

Our topic for today is another rocketry concept: Specific impulse (usually abbreviated Isp).  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:
$Isp equation$  Where:
• $I_{{sp}}$ is the specific impulse in meters per second
• $F_{T}$ the thrust in newtons
• ${\dot m}$ 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, $v_\text{e}$ is used instead of Isp, but the concepts are the same.