i found that a really effective way to get into "the occasional peek into the hero's mental state" is to ask yourself what the hero wants at a particular moment. If you know what he wants, then the drama can unfold.

Several years ago, I discovered someone's technique to analyze and build scenes. The technique closely mimics real life: Establish what the hero wants; Present the obstacles; Allow the hero to fail -- that is, an obstacle bring temporary disaster; the Hero recoils defeated, unsure what to do; the Hero then weights new alternatives, none of them perfect; the Hero implements an alternative (a new "Want") and the cycle continues. Several of the stages in the cycle present opportunities to explain scientific alternatives that the hero is mulling over.

When I write a scene now, I find it fun and exciting to use this technique, which usually yields a lot of new insights and enriches the writing.