Does anyone know why the first stage used kerosene rather than liquid hydrogen & oxygen in the way that shuttle does given that the latter has a higher specific impulse so less fuel would have been required? Presumably the rocket would just have been too large or were there other reasons?
The Saturn V was
really pushing the state of the art - and the F1 first stage engines were several times more powerful than anything previously attempted (1.5+ million pounds of thrust). While H2 engines have a huge specific impulse advantage, kerosene is much easier to deal with since it's not cryogenic and H2 is far less dense that kerosene of the same impulse, so the first stage would have gotten even bigger. Also, the first stage is, as noted, only there for the first 80 seconds. It basically was cheaper, easier, and
safer to simply make the first stage heavier and use kerosene, rather than 'optimize' it by using H2. The upper stages, being far more weight critical, used H2 (I don't recall the specific number, but one additional pound on the third stage added something like 20 lbs. of propellant needed to the first stage).
It's basically the same reason they used the Solid Rocket Boosters on the shuttle (solid boosters have worse specific impulse than kerosene).
BTW, my understanding was not only was the failure of an SRB to light catastrophic, they needed to light within a few milliseconds of each other to avoid catastrophic loads on the shuttle stack. Given how hard it is to light ammonium perchlorate (AP) based propellant, I always thought that a bit scary (we use a very similar AP based propellant in hobby rockets, and 'misfires' (failure to light) are not uncommon).
