People are sometimes confused about what to call the “whoosh generators” that we use in our hobby rockets. Estes, the largest manufacturer, calls them “rocket engines” (though they have some exceptions), while other manufacturers, like Aerotech and Quest, call them “rocket motors”. Dictionary definitions are not as definitive as we would like, so here’s the best guide:

Rocket “motor” has been used forever. An “engine” is a type of “motor.” Based on that, the long accepted use in professional rocketry is that solid-fuel rockets are “motors,” while liquid-fuel rockets that use moving parts like pumps are called “engines.” Wernher Von Braun himself interchangeably used both “motor” and “engine” when talking about the projects he worked on. When Orville Carlisle created the model rocket, he called his devices “boosters” or “charges,” borrowing from his fireworks background. G. Harry Stine decided to call them motors, based on what the people at White Sands Missile Range called their rockets. So the first units Vern Estes made for Model Missiles were called “motors.” Later, Vern changed to “engines” based on what he thought he heard from Harry in a discussion about the two terms. And that stuck. Years later, he and Harry were reminiscing and Harry asked why did he change to “engines”? So either Vern misheard, or Harry misspoke all those years ago. And here we are!

The bottom line suggestion is to use “motors” when talking about any solid-fuel rocket unit, except when you’re talking about Estes, where it’s OK to use “engines!”

Here’s MIT’s take on the difference between the two words.