The optional RX-1 Thruster could be added for supersonic flight attempts and was purchased separately. It consisted of a specially-prepared F100-0 motor and a set of Nova fins that were to be attached to the casing with epoxy. It functioned as a CHAD-style booster stage for the Dart and was usually not recovered. With the addition of the thruster, the combined length was 24". The actual kit name was the Dart, and when it was combined with the RX-1 Thruster the result was called the "Mach-1 System.". It was commonly known, though, as the "Mach-1 Dart." Even FSI called it by that name in its price lists. I used a body tube and a set of fins to simulate the thruster; my version can be flown with an Estes D12-0 booster motor inside the "thruster." Of course, my clone will never reach a velocity anywhere near the speed of sound.