I haven\'t made any huge rockets in a while, so I recreated one from a previous version, complete with TMI/Slowdown stage and Lander/Return stage. Here it is on the pad; And here it is in orbit, boosted horizontally solely by its evidentially-not-useless second stage. First stage apogee-88KM Looking it this, it seems you need; -Relatively large first stage, but too large-diminishing returns (and make sure it has enough thrust) -Smaller second stage-but still quite big -relatively small later stages.