If you check the ship's Imperial Registry Number or IRN, you see NS-U1 at the beginning. NS is the ship type, Naval Scout. The U1 is the fleet type. The Heartbreaker, Seisenkyo and all of the various shuttles comprise the First Uesu (Recovery? Expeditionary? Exploratory? Investigative?) Fleet. They report back to the people in charge of Gemini Star Fortress that we left from originally. Technically they could just be another Expeditionary/X labeled fleet, but I thought it would be cooler to give them a new type of registry for their secret mission. And, if we ever find Uesu or something just as important, the fleet might be made public and have more ships assigned to it to deal with whatever is found.