Hi everyone, I’m trying to predict the maximum height of my rocket flying straight up in the kerbin atmosphere and am stuck.
My ship is one flea booster with a Mk1 pod and a Mk16 chute flown by a kerbal. It weighs 2.44t full and 1.39t empty. The flea has an ISP of 140 asl - 165vac. Using the asl ISP I got 772.0166 delta v. From here I used some kinematics equations and figured that the speed at the end of the burn should be 685.16m/s and the maximum height of the flight would be 23926.72m
When I tested it out in the sandbox with drag turned off I ended up going 29606m high and the speed at the end of the burn was 704m/s
So I think the numbers were off because as the rocket flys up the ISP improves meaning I actually had more delta v than calculated. Another thing I thought might have affected it was the force of gravity changing the further away from kerbin I got (I used a constant 9.81).
How do I improve my calculations to account for changing ISP and gravity? Or was I missing something else? If anyone is feeling ambitious I would also really appreciate an explanation of how to add drag in as well because the formulas on the atmosphere wiki are not making any sense to me.