The fun when writting this story is, once I grasped the rocket equation I started playing with it - and uncovered some possibilities never thought or never build.
One other example
Takes Dynasoar on a Titan III.
- two solid fuel SRMs
- Titan stage 1 (2*LR-87s)
- Titan stage 2 (1*LR-91)
- Dynasoar on top
Now, blend Dynasoar with the LR-91 stage 2 to get a fat rocketplane.
Put that on top of one SRM. Scrap everything else.
The SRM provides 2 km/s, the rocketplane assumes the rest of the ascent, +7km/s to reach orbit with a small payload (2 mt in a good day).
Well, there is a simple, two-stage system: fully reusable if the SRM is recovered at sea, Shuttle style.
The rocketplane itself can even add a pair of J85s for landing flyaround and still it goes into orbit with a small payload. And it doesn't even burn deep cryogens: a very ordinary kerolox gas-generator (Titan I LR-91 for example) can do the job, perhaps with LOX replaced with N2O.
No drop tanks either.
9.81*270*ln((500+50+1)/(50+50+1))+9.81*316*ln((50+1)/(10+1))
= 9248 m/s ; with 1 mt of payload.
Even with bad isp and bad propellant mass fractions (0.80) it goes into orbit.
