Typing "rocket motor" into google returns a page full of links mostly about rocket engines. It seems that The Google has AI-synonymized them.
Question: Can "engine" and "motor" be used interchangeably in spaceflight? Are there any cases where they can't be (apart from proper nouns; the names of specific engines or motors).
Asking The Google's ngram viewer instead of The Google's search:
British English:
American English
"Motor" by convention refers to a solid rocket, "engine" by convention to a liquid rocket. There can be exceptions.
...the word "motor" is as common to solid rockets as the word "engine" is to liquid rockets...
Rocket Propulsion Elements, Sutton, 4th edition, p. 354
Anecdotally, at least on shuttle you could get away with calling a liquid engine a "motor" more than calling a solid motor an "engine". Anyone referring to the "solid rocket engines" would have gotten funny looks.
And then there are "jets" and "thrusters". It all depends on the cultural jargon of the program you are working on.
According to Wikipedia, they are effectively interchangable:
Motor and engine are interchangeable in standard English. In some engineering jargons, the two words have different meanings, in which engine is a device that burns or otherwise consumes fuel, changing its chemical composition, and a motor is a device driven by electricity, air, or hydraulic pressure, which does not change the chemical composition of its energy source. However, rocketry uses the term rocket motor, even though they consume fuel.
However, despite the technical interchangability, it seems to be vastly more common to refer to solid rocket motors and liquid rocket engines.
While the "rocket engine" vs "rocket motor" angle is already adequately covered, I would like to note that the question as asked contains an additional nuance:
Can "engine" and "motor" be used interchangeably in spaceflight?
It's not uncommon to cut the "rocket-" part, using just "engine" and "motor" alone. But this introduces ambiguity with other on-board equipment. While no other propulsion than rockets is used, you can find plenty of other uses for powered equipment on a spacecraft. These are not completely interchangeable.
Consider for instance: "The docking attempt failed due to the failure of a small motor." This "motor" could plausibly be both a little RCS rocket engine, or some electric actuator in a docking mechanism. The second interpretation goes away if "engine" is used.
Non-rocket meanings of "engine" and "motor" still exist in the spaceflight namespace.
additional supporting evidence of a distinction dound in CNN's Pentagon tracked failed Iranian satellite launch and new images reveal Tehran is set to try again:
While the US defense officials did not identify the rocket that was used in the launch earlier this month, Jeffrey Lewis, a professor at the Middlebury Institute of International Studies, said it was likely the Simorgh rocket, a two-state space launch vehicle using engines based on a North Korean design.
Nevertheless, Lewis suggested Iran would develop a different rocket if it pursued ICBMs, saying, "The Simorgh is huge and uses engines that are basically super-sized Scud engines, which are pretty inefficient. If Iran wanted to build an ICBM, it would follow North Korea's path and build an ICBM with a better engine or motor and small enough to be transported by a truck."
