It took 83 engines to get to the moon

Originally published at:


Space pedantry time!

A motor is a device that supplies motion or motive power; typically converting electricity or fuel into directional thrust by way of rotation, but not necessarily. Rockets, linear actuators, and automobile engines are all motors. In fact nearly every engine is a motor!

An engine is a device crafted by the ingenuity of man that harnesses multiple moving parts to achieve a goal. Every Rube Goldberg or Heath Ledger device is an engine, but a shaded pole electric motor is not an engine because it’s too simple - only one moving part. Similarly, the ullage motors of the Saturn V are not engines… too simple.

Liquid fueled rocket motors can be on the fence between engines and motors, as there are grey areas - how simple is too simple? But the Saturn V’s five F1 motors are most definitely engines - even the simplest incarnation has a kerosene/LOX gas generator driving a turbine driving multiple pumps to manage fuel pressure and distribution, and the four outer engines used gimballed nozzles to provide pressurized thrust vector control. The F1 motor is complicated and ingenious, and thus it is clearly an engine.

I’ve spent a lot of time in a rocket motor factory, and my late father was on the team that built the ullage and LES motors Ms. Teitel mentions. I can’t remember a single time anyone called a solid fuel motor an “engine” without being (good naturedly) ridiculed for doing so.


What? Come on, how can any of this be true when the Earth is flat. :yum:

Fake! You can’t know so much about motors and rockets and engines with a name like, ‘Medievalist’! Heresy!

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Pah, he’s just keeping up with the latest developments in familiar technology:


True Story, so help me, although abbreviated for this forum.

As a young man I got a job in a rocket motor factory, and the older guys were very suspicious of me.

They said “Every person who was ever any good at the job you’re supposed to do was noticeably weird, if not completely insane. You appear to be a normal and well adjusted human being. You cannot possibly do this job well.”

I said “For fun, my friends and I do full contact armored medieval combat. This scar in the middle of my forehead is from a helmet failure.”

They smiled at each other with relief and said “Welcome to the team!”


NASA refers to them as “solid rocket engines” (rightly or wrongly). (At Rocketdyne, we – without exception – simply referred to them as “solids”, only).

I wouldn’t say “solid fuel motor”, since the propellant is a combination of fuel and oxidizer.


I’ve always enjoyed the motor vs engine discussion (rocket hobbyist), and I appreciate your descriptions.

I had not heard the term ullage before so headed over to Wiki, and wiki identifies the ullage as both a motor and engine in the first sentence lol!
“Ullage motors are relatively small, independently fueled rocket engines that may be fired to accelerate the rocket prior to main engine ignition”

The discussion continues…


That’s actually a great qualifier!

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@hecep, admittedly my personal knowledge is old; I still have trouble remembering that North American Rockwell’s engine designs are Aerojet Rocketdyne’s now. :slight_smile: Most solid rocket fuels, in my day, were composed of fuel and oxidizer compounds held in a rubber matrix - all materials involved being in the solid phase of matter. We used giant mixers that looked like the cake mixer on a kitchen counter scaled up to titanic size, in spark-free sheds with blowout walls.

@vonbobo, I wouldn’t trust Wikipedia on the intricacies of rocket motor technical jargon (they have film critics rewriting articles on farm equipment over there), but, language does evolve!


Current “heritage” Rocketdyne employees have trouble remembering that, too! No… love… lost.


Absolutely. I simply enjoy how many “definitive” yet different descriptions there are on the topic.

I actually heard the collective rocket nerds groan when the video’s graphic tried to explain the difference.

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Actually, I believe the third stage was crashed into the moon only one time time, so the impact could register with seismographs left on previous flights. Most of the time, they just flew right past into perpetual orbit around the sun.

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The ullage engines on the Saturn V were bi-propellant (the ones on the third stage anyway), so there must have been at least two valves, so I put it to you that these deserve the name “Engine”.
In fact, looking closer, there was dual redundant fuel feeds, therefore at least four valves.

Motor/engine semantics aside, I only counted 70 to get to the moon. The other 13 got them back. So, 70 engines to get to the moon. Not so impressive anymore is it.


Ah, there’s the source of what @vonbobo mentioned before, I think. It appears there are liquid fueled engines as well as solid fuel motors on the Saturn V ullage ring.

The solid fuel motors were no doubt smaller, as they were used only to separate the ring from the upper stage. My father was only involved with the production of those motors, the ullage engines were created by another team.

EDIT: I took a sec to check my memory against the mighty Google. It appears that some of the Saturn Vs used only solids on the ullage ring, others used liquids as well. I don’t have time to do proper research right now, unfortunately.


That one time (assuming it was just one time) was on the Apollo 13 mission.

I endorse this mixing of head battering with lethal cudgeling and rocketry! Carry on!


Things can get confusing when word have both specific and general meanings. Eg. "ship: can mean any largish ocean going vessel, or it can man a sailing vessel that has three masts with (at least) three square sails on the first two and two on the last one. Similarly “missile” can mean ANY projectile (as in "missile weapons). But the word “missile” is often used to mean “guided missile” as opposed to “unguided rockets.”

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I made a point to one of my kids recentlly (we were watching Apollo footage to combat some YouTube conspiracy theory bullshit) -

We not only landed 12 men on the moon, we landed 6 entire launch platforms and rockets there, and managed to launch 6 rockets off of the moon successfully.

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