As for "lithium cracking", this need not refer to lithium being cracked (a process never really called by such a name in reality, as "cracking" is already reserved for a specific petrochemistry process). It might just as well refer to cracking taking place with the help of lithium. Remember that the place was visited by ore transports - and it would make very little sense to haul ore to this remote location from more central ones, but a lot to haul it to that location for refining and the eventual hauling of the end product to the distant civilization. Why haul in lithium ore for cracking, when lithium is actually fairly abundant everywhere (as long as we accept the ubiquity of Earth-like worlds)?
Since this is the 23rd Century with little need for petrochemistry I don't see why "cracking" shouldn't apply. Of course, "tritium breeding station" couldn't have been an alternate choice but then most viewers would have asked
a) What is tritium?
b) What is it good for?
By going for "lithium cracking station" that skipped the first question and just left "What is it good for?".
Furthermore people familiar with nuclear fission would have pointed out that tritium is a waste product of nuclear fission reactors so why even go through the hazzle of devoting a whole planet to the production of this waste product?
Somebody familar with nuclear fusion would have understood that this planet produces nuclear fusion fuel and that dirty nuclear fission is rather outdated by that time (although other TOS screenwriters apparently felt differently, unfortunately).
I see no contradiction that the "ore ships" transport the (rather rare) lithium to Delta Vega where it is converted to fill the "fuel bins" of Delta Vega.
My whole point: Here we have the proof that nuclear fusion (at the good riddance of nuclear fission) is in widespread use during the beginning (!) of TOS. Why deprive ourselves of that opportunity and instead deal with these unconstructive hints towards nuclear fission? If you can master controlled matter-annihilation then controlled nuclear fusion would have been a discovery on that path of a believable technological evolution.
Alternately, of course, we can assume that Delta Vega actually produced antimatter and that "lithium cracking station" was a cover to avoid unnecessary attention.
Also, if impulse drive combines power from fusion and propellant from fusion exhausts, it is likely to consume onboard resources faster than warp drive - a curious fact indicated in "The Doomsday Machine" where sustained impulse maneuvering is a pressing problem for fuel reserves whereas warp maneuvering never ever was. Impulse movement might involve shooting out both waste helium and unfused deuterium, as the latter would be not just an available energy source but also the one available source for propellant mass (unless the ship carries a separate substance for propellant, which would be a bit silly - or unless impulse drive involves no Newtonian propellant exhaustion, which actually sounds rather likely).
Yes, we've seen that "power failure in
the main energizers" leads to loss of deflector shields, instant phaser power and warp power.
DECKER: Mister Spock, status report.
SPOCK: Warp drive and deflectors will be out for a solar day.
Repairs proceeding on transporter and communications.
SULU: It's closing with us again, sir.
DECKER: Maintain speed and distance.
SULU: It's sucking in space rubble from those destroyed planets. Refueling itself.
SPOCK: We can maintain this speed for only seven hours before we exhaust our fuel
, but it can refuel itself indefinitely.
It would indeed appear they had to rely on "battery power" (i.e. pure nuclear fusion energy) for impulse drive where the use of the main energizers might have enabled them to turn that pure nuclear fusion energy into an "exotic" one providing greater thrust.
Interesting: No reported (permanent) damage to the dilithium crystals but merely a temporary failure of the "main energizers" that seem to require one day to cool off and/or to be repaired. I can't help but feel that it looks a lot like what happened in ST II.
However a clear indication that you need the "main energizers" to work with the dilithium crystals to produce warp power!
As for the deeper meaning of "energizer", I'd go for the invigoration aspect.
I concur and there is another hint that "the energizer" (i.e. one energizer!) in "The Alternative Factor" only supplied the crystal regeneration drawers with energy.
Lt. Palmer clearly refers to "main energizers" (i.e. more than one) that are probably those "power plants" Spock mentioned earlier in that episode.
By the time of ST II they have apparently been able to reduce main (and secondary) energizers down to one.
Nevertheless, I concur with blssdwlf's conclusion that dilithium crystals are able to release enormous burst of energy (mabe that's their amplification or oscillating effect?).
In ST II the energizer is "out", yet when Spock removes the casing we see an obvious burst of energy, suggesting that was the energy stored by the crystals.