TUKWILA, Wash. — Thirty years after the first flight of a pioneering reusable rocket ship known as the Delta Clipper Experimental, or DC-X, a commercial venture is aiming to bring its legacy to life in the Seattle area. Even its name — New Frontier Aerospace — is a callback to the earlier days of America’s space effort, going back to John F. Kennedy references to outer space as part of his “New Frontier.” “We’re sort of like the grandson of DC-X,” New Frontier’s co-founder and CEO, Bill “Burners