I'm currently reading "The Space Shuttle Decision" by T.A. Heppenheimer, which discusses the planning in the late 1960s for a reusable successor to the Saturn r

I'm currently reading "The Space Shuttle Decision" by T.A. Heppenheimer, which discusses the planning in the late 1960s for a reusable successor to the Saturn rockets. One interesting thing is that they then envisioned this to happen in phases: a "type I" partially reusable vehicle (with expendable fuel tanks and maybe expendable boosters), then a type II fully-reusable rocket-propelled vehicle (probably two winged stages which both fly back), and finally a type III air-breathing vehicle (Skylon-style air liquefaction was talked about already then). The more advanced concepts cost a lot of money to develop, but reduce the per-launch cost. So the hope was to start with a type I vehicle (the eventual Space Shuttle) to reduce launch cost and grow the market, until there are plans for so many launches that it makes sense to fund the advanced types. In hindsight, the Space Shuttle unfortunately kind of botched the reuseablity. But with SpaceX we finally seem to be on track to having a working partially resuable launch vehicle. Maybe this will "unfreeze the future"---with a bigger launch market and commercial pressure people might be tempted to go for something like Skylon rather than more of the same in follow-up Arianes...