Mich. Comp. Laws § 259.781

Sec. 1. As used in this act: (a) "Model rocket" means an aero-model that ascends into the air without use of aerodynamic lifting forces against gravity and is propelled by means of a model rocket engine. (b) "Model rocket engine" or "engine" means a device or combination of devices which provide the necessary force or motive power to cause the model rocket to move through the air.