Definition of Specific Impulse

Extract

Two recent contributors to Technical Notes have expressed the view that, in rocketry, specific impulse should be defined as thrust/mass of propellants consumed per second, rather than as thrust/ weight of propellants consumed per second. The only reason given in support of this view is that the weight of a given mass varies with location. Our purpose here is to give reasons for taking the opposite view, namely that the second definition is preferable.