A reader remarked on missile launch systems before the more recent North Korean launch of 5 missiles:
Wild ass guess on liquid fuel rockets: easier to build, more control over thrust amount and direction might make them more accurate and/or easier to direct to location. Solid fuel is light it and forget it — basically a contained explosion until it all burns up. And often, they explode if not made just right — or even during the making.
Clarification on “easier to build”: liquid handling systems, pumps, plumbing, etc. all complicated to build, but are mostly “knowable” problems of managing liquids. If you use relatively stable things like hydrogen peroxide and kerosene, it’s even reasonably safe (liquid oxygen gets harder, hydrazine is probably entertaining). But solid fuel, while conceptually simply is a bugger to get right: stable mixtures which burn at just the right rate without going boom or burning through the shell (see Challenger). Mixing up that glop without it igniting is a challenge, too.
But I’m not a rocket scientist.
I do recall, during the breakup of the Soviet Union, talking to someone who stated that many Soviet Union missiles had gone stale, meaning that their liquid fuel launch systems had actually deteriorated. They consisted of two separate containers of material; launch consisted of mixing them and, I think, standing back. One of the materials had a very limited lifetime, apparently.
