I'm in the middle of a hard-mode career game and I've unlocked turbojets, ram intakes, etc. so I've started investigating plane-based SSTOs, mostly in order to cut costs so I can unlock the next tier of KSC builds sooner. Unfortunately, all the old tricks I knew about building heavy-lift and long-distance SSTOs no longer work. Multiple intakes per engine, turbojet/nuke combos, etc are all off the table. Reading around, the vast majority of SSTOs people are showing off lifting payloads to orbit or visiting minmus, etc. feature RAPIER engines. Since RAPIERs are now at the far end of the tech tree I can't utilise them. Is it possible to build a non-RAPIER SSTO that can do useful work any more? I've managed to get one into orbit running with quad turbojets and dual reliants but with no cargo and barely enough Delta-V to de-orbit, let alone travel elsewhere.