What's the smallest kerolox engine that is/was used for spaceflight?

Question

This comment linked in this answer to the question How does the camera make the exhaust of the Electron's RP-1/LOX exhaust transparent? says

Some quick calculation suggests the thickness of the exhaust plume from a Rutherford is about 1/6 that of a Merlin 1D, 1/18 that of an F-1.

This led me to wonder if the Rutherford is the smallest RP-1/LOX engine to be used in spaceflight.

Is it the smallest for orbital launches?
Have smaller ones been used for suborbital spaceflight for scientific purposes?

@RussellBorogove 470 Newton "rocket engine"! http://www.astronautix.com/p/p4-1sustainer.html this one stands out in a quick check, but I'm not sure it can go to space. "The P4-1 (a.k.a. LR64) engine was also manufactured for the AQM-37A target drone." so I guess not. — uhoh, Feb 03 '19 at 01:32
perhaps http://www.astronautix.com/r/rs-36sustainer.html at 9.21 kN. — uhoh, Feb 03 '19 at 01:39
To make your question a little more granular, does it matter if it's used singly or in multiples? — Snoopy, Feb 03 '19 at 05:34
@Snoopy to me it doesn't matter, no. As long as it is involved in getting to space or being used in space. — uhoh, Feb 03 '19 at 05:46

Organic Marble · Accepted Answer · 2019-02-03T14:42:01.477

5

I'll start off with a guess - the early Atlas LR-101 vernier engines, originally 669 lbf (as low as 526 lbf in some configurations), later upgraded to 1000 lbf.

Visible in this picture firing to left and right.

Beautiful image from here

Schematic from, and good information, here

Cool picture of this little engine mounted on its pitch/yaw gimbal. It looks like a spotting scope. from here

edited Feb 03 '19 at 14:42

answered Feb 03 '19 at 14:32

Organic Marble

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these aren't as small and didn't go to space, but they are kind-of cute https://youtu.be/pqCatb2oApU – uhoh Feb 24 '19 at 07:37

What's the smallest kerolox engine that is/was used for spaceflight?

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