A split infinitive, as we generally understand the term, is a “to [verb]” construction with an adverb stuck in the middle of it. In the Star Trek example, then, an unsplit infinitive version would be “Boldly to go where no man has gone before” or “To go boldly where no man has gone before.” If either of those sounds better to you, be my guest. To me they sound as if they were translated from the Vulcan.
