Usually thrust vectoring for the whole rocket is done by changing the orientation of individual engine(s) by hydraulic/electric actuators. So in this system the engine simply moves and with it the trust vector moves too in the exactly same direction.

I wonder whether a solid state thrust vectoring could be used where the engines would not move at all (be static) and instead the thrust of individual engines would be changed to provide a final 3D thrust vector by vector addition of thrusts of individual engines. Of course such setup would only work for a configuration of multiple engines (at least 3 engines for 3D vector) since the vector of single engine would still remain the same (only thrust would change).

I have not found such "solid state thrust vectoring" system in commercial usage. Are there any problems with this solution? Such system would have fewer parts any may be more reliable. I am interested in classical bell nozzle engines mainly.

As a side note I found a company that is developing a 3D printed aerospike rocket engine with solid state thrust vectoring (video, site) where the single engine has its chamber split into 3 parts to provide 3D thrust vector so it looks like solid state vectoring with aerospike may be doable but the system has not flown yet.

Edit: I just learnt there is a term called "differential thrusting" which is what I meant by "solid state thrust vectoring" (nice question). For additional small engines there are the Vernier thrusters and sometimes RCS is mentioned to also work for attitude control.

  • $\begingroup$ @uhoh I have reworded the question for better clarity. I mean a system where engines do not move themselves. "open valves that squirt chemicals in the sides of the nozzles" - yes this looks like "solid state" for me - is this system used somewhere? $\endgroup$ – Kozuch Feb 19 at 11:38
  • $\begingroup$ There is at least any satellite interceptor that used an array of solid motors for terminal guidance but google is failing me on finding a good source $\endgroup$ – GremlinWranger Feb 19 at 11:40
  • $\begingroup$ @uhoh With single gimbaled (mechanically actuated) engine there is no vector addition. It only has a single vector that changes it's orientation and results alone in final thrust vector. $\endgroup$ – Kozuch Feb 19 at 12:33
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    $\begingroup$ It may be quite inefficient for a long rocket where center of mass is very far away from center of thrust. However for a compact configuration such as Perseverance landing stage, differential thrust is a great way to get rid of actuated engines. $\endgroup$ – qq jkztd Feb 19 at 12:41
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    $\begingroup$ in addition, a minimum of 4 engines (not 3) pointing away from resultant thrust vector would be required to provide full attitude control. (allowing roll control) $\endgroup$ – qq jkztd Feb 19 at 13:12

Some solid rocket motors provide thrust vector control by injecting fluid into ports around the nozzle. In this system, neither the nozzle nor engine is gimbaled.

Vehicles that utilize(d) this system include later Titans and the PSLV.

My answer to this question includes a description of the Titan system with schematics: What was the purpose of the small red tank attached to the Titan-Centaur launcher?

Ohsin's answer to this question describes the PSLV system with photos: How does a single SRB control attitude?


I don't know of any source that would give a comprehensive survey to this kind of question, so answers are probably going to come from people who remember specific examples. If they remember which ones to look up and verify. I've seen some but can't remember which ones, so I haven't said anything.

But I just read about the Japanese Mu-3 family of rockets, which have their own variation of the fluid injection approach. Organic Marble referenced the Titan II, which injects dinitrogen tetroxide in the nozzle, and a post which discussed ISRO's Polar Satellite Launch Vehicle, which injected strontium perchlorate.

The Japanese Mu-3 family were three- and four-stage solid rockets, plus boosters, in use from 1975 to 1984. The Mu-3C and Mu-3H used fluid injection in the second and third stages; a combination of freon to suppress combustion and hydrogen peroxide to enhance it. The Mu-3S used the same in the first stage, but hydrazine instead of hydrogen peroxide in the second stage. The Mu-3SII had the same first stage, used only freon in the second stage, and freon and hydrazine in the third.

I got that from Bernd Leitenberger's Raketenlexikon Band 2: Internationale Trägerraketen (2009), pp. 303-314.

A quick check online found an article about the Mu-3S. It seems that the 3S first stage only had freon, not hydrogen peroxide. It also mentions "sidejets" in the second stage of the 3C and 3S, by which they seem to mean a reaction control system (the little rockets that control attitude) powered by hdyrogen peroxide. I didn't notice that Leitenberger mentioned those.

Anyway, discrepancies aside, you can either enhance combustion or suppress it by injecting various chemicals, and it doesn't have to be exactly the same in each stage.


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