This is the U.S.S. Excelsior. This ship first appeared in Star Trek 3: The Search for Spock. It was known as "The Great Experiment." The original idea in the Star Trek arc was to have Kirk find Spock, save the world and then be awarded the Excelsior. Fans weren't thrilled with that idea. So under pressure of the fans, the powers that be decided to give back a Constitution class sharship and number it NCC-1701/A. But the Excelsior went on to become Captian Sulu's ship, a then modified to become the Enterprise B. This ship appeared in the Next Generation and other incarnations of Star Trek.