Good point, I didn't think of it that way. Interestingly, the mass of the rocket is about 13,150 kg, which is 128,870 newtons of force on the ground. The thrust of the rocket is 5MN... i'm not sure if that mass includes fuel and i'm also not sure how fast the weight decreases from spent fuel, but interesting, nonetheless. It looks like it would be a differential equation (variables in gravity as it launches, changes in weight as fuel is spent, etc). I'd love to see the math, somewhere.