I didn't really get a lot of
work done at work today, but I drew more big dumb rockets!
Two things had bothered me. First, these are
all huge vehicles. If you can't scale down to less than 150% of a Delta IV Heavy, you're probably not going to end up flying many vehicles. Second, it wasn't obvious how the 34MT variant could use the same launch facilities as the other single-bore variants. Shuttle did all hold-down through the solid motors, and our solids are too damn small. If you can't share facilities, what's the point? But if you get rid of the 34MT, then things get even sillier.
No, what we REALLY need, clearly, is a half-brother family using as much of the same technology and facilities as possible. I wondered about Ares I, and what similar solution we might explore here. Two Shuttle-derived solids of various lengths, with a liquid stage on top. For no particular reason I elected to go with 6.5m diameter, which it turns out is the Saturn V third stage. This certainly aided calculations.
A single J-2X was selected, in lieu of more TR-106, because the Isp is great and it's already certified for vacuum start/restart.
We end up with a pleasing family of launchers that could use all of the same facilities as the 8.4m reusable set I posted previously, all with a single throwaway liquid engine and recoverable solid first stage. The set spans the range of 18MT (about 20% bigger than the smallest common Delta IV variant) to 34MT (about 20% bigger than a D-IV-Heavy, and big enough to launch HL-42). If desired, we could probably launch entire without ullage thrusters, since the space directly beneath the J-2X is clear and open, but that's left as an exercise for the reader.