thx guys. but in the meantime i figured out the launch problem is related to the remotetech mod, which needs an additional part for unmanned craft to "connect" the probe to the KSC to have control about it, later for sure it is possible to drop this part with the initial stage because it has 500km max range, by this time you need to have at least one comunication part active which is provided with stable electricity support and also an working satelite network already established to leave planet Kerbin far away above 500km (only for unmanned) @all, espacially to Sirine >> this mod is very nice, like most of the mods which dont change the physics behavior or manipulate the basic gameplay at all @tweety, i am very noob with mechjeb, i play classic career science mode, so i havent all mechjeb features yet, and not much knowledge about that tool anyway, i hope a friend can answer my questions about it in my mother tongue but seriously, for now i liked to know what is this TWR, what stands it for and how it influence my vessel.. one more thing which i dont understand is, if i would put those nose from the aerial section on top of my LFO boosters, it decrease my Atmo delta V in this mechjeb deltastats window, but should it not increase this?? and the second question shouldnt have any relations to the initial issue i guess too and about the struts, okay this is exactly what i thought, one is enough, i mean in the tut vids they build always two on each side of one LFO to connect it to the main engine for example, surely symmetrie psychos hehe but i give it a try to connect only one on top (it will probably save x<1% of mass hehe), but definately it is better to make a strut between 2 LFO booster in my experience, but this is a question of design the whole rocket anyway