On 26/03/14 01:50, Ed LeBouthillier wrote: > So, the whole issue of Ve = g Isp is, I think a product of the units > that I decided to express Isp in. > > > > Is Isp to be expressed in units of seconds or in meters/second? I > chose units of seconds. > I think of it as a choice between weight-specific impulse, with dimensions of impulse per unit force (weight), i.e., time, and mass-specific impulse, with dimensions of impulse per unit mass, i.e., velocity. To me, specific impulse is, by convention, weight-specific impulse. I enjoyed the book, thanks very much. If I may point out one spot where I think there is a bit of a units issue, it's in the discussion of pressure-vessel performance factors on page 76. Two versions of the definition of performance factor have crept in. In the first, it's defined as p*V/mass, which has dimensions of energy per unit mass and in the second as p*V/weight, which has dimensions of length. The numerical examples seem to have been calculated with the weight-based version of the equation assuming g=10 m/s2, but that factor of g does not appear in the numerical example. Why not just use the mass-based version and express PFs in J/kg? Nels Anderson