Theysen

Robocraft? You already have a huge advantage as KSP veteran when it comes to building at least I guess

Right click the Boosters in VAB and set a thrust limit, which will reduce the acceleration and gives you even more delta V!

Thank you very much Jesrad, I simply forgot to lock the tanks and ended up with less fuel to be burnt by the rocket, didnt check that the small hardpoints don't lock the fuel crossfeed! Got it into orbit now and I am kind of hooked with more designs like this. Tyvm!

Can you give some flight instructions? Tested the exact first layout and didnt make it to orbit at all.. Do you go vertical at some point like the current spaceplanes design during ascent? I really would love to know as I like this approach of a crew shuttle!

Besides solar panels also lose their effectiveness over the years e.g. by radiation (just to name one factor among the others) in space environment. It's an decreasing exponential function. Due to this fact RTGs are the go to in the real world so I don't see a problem by making them infinite power sources.