Hi guys.
I've recentrly crafted, in the hangar and in orbit around Kerbin, my biggest ship. It was intended to beat the Jool-5 challenge. I got him out of Kerbin's orbit with a mainsail, and I had already noticed it was longer than usual. Then around Kerbol's orbit, I did a maneuver node, the delta-v needed was around 350m/s, and my engine was the nuclear one, that thrusts at 60kN. Only, the burn time was over 15 minutes, and it wasn't a display bug from KSP. Is this normal? I thought in space the weight of a ship didn't matter. I precise I have no particular mod. I've already put about 200h into the game and this problem has been so frustrating I signed up here. Anyways, I really need your help, kerbonauts!