Thanks for all yout comments! I've learned a lot reading this forum. I must admint that i killed two kerbonauts trying to landing mun, and this is the first time y get to Mun and back successfully The lander, as you can see, is small, about 6.5 tons. One T-400 fuel tank and 4 T-100 fuel tanks, which are decoupled after liftoff Mun, to reduce mass. Now i have to learn rendezvous and docking, so i can buil a space station in Kerbin orbit and a base in Mun. Thanks for all your replys and your ideas!!