S.1 Spacecraft Propulsion Systems Chapter 1: Introduction to ...

Thruster-specific Impulse
F
I sp = [Ns/kg]
o
m
Isp = thruster specific impulse [Ns]
F = thrust force [N]
o
m = Propellant mass flow rate [kg/s]
- 8-
Specific impulses are often quoted in units of seconds, corresponding to a modification of the
above definition to that of the impulse delivered per unit of weight of propellant.
The values in seconds then follow from those in Ns/kg by division with the gravitational
acceleration standard, g (=9.82 m/s 2 ).
with:
I sp
o
=
F
o
mg
0
o
m g = w
=
F
o
w
[s]
0 [kp/s] in propellant weight flow unit