Not exactly sure where to put this, but how would I go about calculating the paylad of a given launch vehicle to LEO? I always see people saying things like, "well, this gives you x tons to LEO, add another SRB and you get 2 more" - how do I calculate this? Is there a program I could get hold of?

I don't know of a program to work it out - it's probably a more complex simulation to get accurate figures than Joe Public could manage (although perhaps using something like Orbiter one could simulate a fairly close approx.)

Most of the figures are out there for current or near-future LV's already though...they have to be in a commercial launch context so people can know what they're looking at www.astronautix.com is a great starting point, and hunt for Launch Guidelines or Payload Guides etc as PDF's at various LV manufacturers websites ( Ariane, Starsem, Pegasus, Atlas V, Delta IV, II all out there I think ) which give extensive versbose launch capacity specification.

Doug

But clearly Orbiter has a mathematical basis on which it makes these calculations? Astronautix does have a lot of figures but not for new launch vehicles.

Well - not a set of calculations...it's just a simulation of what goes on.

Best place to start would be to google for 'The Rocket Equation'

Doug

To do an accurate calculation, you need to know the sea-level thrust and specific impulse of first stage engines, second stage vaccuum <more or less> thrust and impulse, third stage etc.. their mass fractions, burn profile, etc etc etc... that's to get a good (maybe 10%) approximation.

The Devil is in the Details.