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@DavidHammen's answer to Engine failure: how to detect? mentions thruster sensors.

This intrigued me and so I thought I'd ask about how this is done.

Thrust is a critical parameter to know in real time, and when there are more than three engines you can't even unambiguously infer each engine's thrust from z-acceleration, pitch and yaw.

Instead you'd like to have a direct measurement.

Question: What are the various ways that rockets measure the instantaneous thrust of each engine? Is it as easy as slapping a standard strain gauge on each strut or mount holding the engine and feeding the numbers into a formula that corrects for geometry? Are there different or perhaps unusual ways this measurement has been made?

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    $\begingroup$ I mentioned thruster sensors. Thrust sensors (aka accelerometers) may not be a good idea. $\endgroup$ May 31 at 12:50
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    $\begingroup$ No one does this that I know of in flight - attempt to directly measure thrust. It's all based on Pc. $\endgroup$ May 31 at 12:59
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    $\begingroup$ @OrganicMarble Mini AERCam did exactly this, and it worked, easily. A puff or two from that vehicle's orthogonal cold gas thrusters made the vehicle respond very nicely. This motivated the managers of X38 to do the same with that vehicle, and I'm sure it would have worked (that may be biased; I wrote the software). NASA/JSC had NASA/Ames look into the problem and develop an alternative frequentist approach to my Bayesian approach. So they paid for my time plus NASA/Ames personnel time plus oversight time. As expensive as chamber pressure sensors are, those sensors would have been cheaper. $\endgroup$ May 31 at 13:10
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    $\begingroup$ @OrganicMarble for completness, please explain what "Pc" is here $\endgroup$ Jun 1 at 17:46
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    $\begingroup$ They right-click on the engine and look for the thrust readout. $\endgroup$
    – Vikki
    Jun 1 at 22:20

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