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Not long ago, I was researching the scaling of converging-diverging de Laval nozzles to subminiature (1.5 mm throat diameter) dimensions for a non-rocket application, and later on studied the potential for making Cubesats fly around with thousands of m/s dV of hypergolic chemical rocketry. (A man can dream.)

Strangely, I found remarkably little information on either topic. Most high-dV cubesat engines are a variant on ion engines, and there seem to be no "subminiature" chemical rockets either in literature or in vendor portfolios.

There are plenty of full-size and "miniature" rockets meant for RCS jets, and there is a tremendous amount of research on "micro-scale" MEMS-based monopropellant rockets you need a microscope to see with fuel tanks smaller than a milliliter, but I couldn't find any information on a chemical rocket engine around 4 to 10 mm in diameter.

Is there a compelling reason for such a thing to not exist even in discussion? Or, alternatively, is there a clear counterexample?

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    $\begingroup$ Liquid apogee engines are within that regime depending on chamber pressure. Probably not what you want to hear but everyday blackpowder engines and composite engines for High Power Rocketry are also in that area. Hybrid rocket engines build by amateuers and student organisations might be interesting. $\endgroup$
    – Christoph
    Dec 12, 2019 at 9:59
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    $\begingroup$ There's no significant use case for a small-size but high-thrust engine,other than model rocketry & perhaps some Army munitions work. $\endgroup$
    – Carl Witthoft
    Dec 12, 2019 at 15:35
  • $\begingroup$ The Gyrojet gun fired small spin stabilized rocket-propelled projectiles either 12mm or 13mm in diameter. They could accelerate to 380 m/s in about 9 meters. en.wikipedia.org/wiki/Gyrojet $\endgroup$
    – Dan Hanson
    Dec 13, 2019 at 21:22

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Our company (Malin Space Science Systems) is collaborating with Stellar Explorations to develop a very small biprop propulsion system for cubesat missions. There is a definite lack of options in this size range, mostly because cubesats have been prohibited from having significant propulsion systems by launch providers or primary launch customer rules up until very recently. Also, cubesats had not started to be accepted for missions requiring high on board propulsion until recently. Some of the challenges of building a system this small is there are no standard parts built for stuff this tiny, so a lot of things had to be custom designed. Also, the scale makes these engines a bit less efficient than their larger cousins simply because manufacturing tolerances begin to limit the lower end of size for some parts so one ends up overdesigning in some areas.

Our system employs thrusters designed to deliver 3-5 N force each. A datasheet is here: https://static1.squarespace.com/static/5c54e307fd67934e24b27846/t/5caa7ce54785d3baf211b7d8/1554677036302/Datasheet+propulsion+2019+03+31.pdf and there's more info on Stellar's website: https://www.stellar-exploration.com/

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  • $\begingroup$ Very interesting (though possibly slightly larger than what I was thinking about). Interesting that it's targeting biprops. $\endgroup$
    – ikrase
    Dec 13, 2019 at 20:18
  • $\begingroup$ The particular mission we were designing for was to insert a 12U spacecraft into Mars medium orbit, including performing the B-plane maneuver. We needed about 2200 m/s to do this and needed to leave about 1/3 of the spacecraft dry mass to execute the mission so that implied Bi-prop level of Isp performance. $\endgroup$
    – Terrance Yee
    Dec 14, 2019 at 6:50

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