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.

  1. Is it the smallest for orbital launches?

  2. Have smaller ones been used for suborbital spaceflight for scientific purposes?


1 Answer 1


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.

enter image description here

Beautiful image from here

enter image description 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

enter image description here

  • $\begingroup$ these aren't as small and didn't go to space, but they are kind-of cute youtu.be/pqCatb2oApU $\endgroup$
    – uhoh
    Commented Feb 24, 2019 at 7:37

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