The name "impulse deflection crystal" was not actually used in dialogue during the movie era, or elsewhere. Nor was the comparable blue thingamabob in ENT called "symmetrical warp field governor" in actual dialogue. But these backstage names do make for good tech continuity when combined with the TNG Tech Manual doubletalk.
The Manual speaks of impulse drive being boosted by subspace coils, but also of the Ambassador
class being the first (for a long time?) to do so. Yet the idea of using subspace fields (or "symmetric warp fields") to reduce mass in order to make STL travel easier is a great one - it defeats most of the real-world objections to the magical performance of the Trek STL engines. Every starship would need those fields, then.
Now, we can assume that some ships have those subspace coils as part of their impulse engines (like the Ambassador
), generating a special field for reducing the ship's mass. But others have this blue crystal, which "governs" or "deflects" the warp field of the warp engines in such a way that the (symmetric rather than propulsively asymmetric) warp field reduces the ship's mass. Hence the two backstage names for the crystal...
Coils in impulse engines would be in fashion during TOS and for Ambassador
; crystal deflection of fields generated by the warp coils would be in fashion during ENT and the TOS movies. And the Galaxy
generation of starships might merge the technologies into a compromise of some sort.
Or then the blue glow, which is unique to the Galaxy
and not present in the otherwise similar Nebula
or "BoBW" kitbash ships, is actually warp glow from the saucer's warp engines, vital for the separated flight mode and apparently used at least in "Encounter at Farpoint" to allow the saucer to reach Deneb IV apace with the battle section. In which case the impulse engines would feature their own built-in coils, as the Tech Manual seems to suggest.
IIRC, in TOS, impulse power could be augmented by other power sources (throwing the kitchen sink at it) and vice-versa, impulse power can boost other systems.
...Including warp, in "Corbomite Maneuver". Unless we interpret that as impulse propulsion
being used to boost warp propulsion
, or perhaps just to create a confusing nuance to the propulsion to shake off Balok's tractor beam.
The main difference was that warp power could be regenerated whereas impulse was a fixed fuel quantity.
Was warp power really "regenerated"? The only time we hear of power regenerating, it is with respect to life support power in "Mark of Gideon" - which could simply mean that the fuel supplies of warp drive would last forever when gradually used for recharging the batteries of life support for just two people.
While TOS writers probably had wild ideas about how warp was fueled or how it worked, none of those were so explicit as to contradict the later, more explicit movie or TNG era ideas about antimatter annihilation and hydrogen-antihydrogen tankage and whatnot.