What type of IMU does the Falcon 9 use? Is it a stable platform aligned with a global frame by gimbals? Or is it a strapdown system fixed to the body of the rocket and therefore aligned not with a global frame but with the rocket's body frame?

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    $\begingroup$ As with many things SpaceX, you most likely will not get a definitive answer to this question. SpaceX is extremely protective of its intellectual property. That said, I cannot imagine they use a stable platform IMU. But that just might be a lack of imagination on my part. $\endgroup$ – David Hammen Feb 6 at 20:19
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    $\begingroup$ Probably not, @a1ex. SpaceX strongly guards its IP. Very, very strongly. If the information is not released publicly (and I could not find the answer to this with multiple search engines) then SpaceX deems the question and answer central to what it does. The only people who know the answer to many of the SpaceX questions at this site either currently work or have worked for SpaceX, and those people would jeopardize not just their careers but their life savings and their homes by disclosing that information. Like most high tech companies, SpaceX has very strict non-disclosure agreements. $\endgroup$ – David Hammen Feb 6 at 20:37
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    $\begingroup$ That said, what you've read about strap down IMUs is correct: They are less massive, less complex, and less expensive. I cannot imagine SpaceX reverting to tech from a previous millennium, but that might be a lack of imagination on my part. $\endgroup$ – David Hammen Feb 6 at 20:43
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    $\begingroup$ I find it highly unlikely that SpaceX uses gimbal IMUs. SpaceX's core design ideology places a big focus on simplicity and affordability. This means reducing moving parts, using cheaper components, and including redundant systems. Gimbal IMU's are mostly a holdout from the days of yore where a digital IMU was too computationally complex to use (the chip in a modern 15$ IMU has computing power to lap Apollo) and using a system with motors and bearings is pointless when a chip can do the same thing but better in basically every way. Realistically, the F9 has many redundant digital IMUs in it. $\endgroup$ – Dragongeek Feb 6 at 20:46
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    $\begingroup$ @Dragongeek As I wrote, stable platform IMUs are a relic from the previous millennium. The Space Shuttle was the one of the last launch vehicles to use stable platform IMUs. But then again, the Space Shuttle was a relic from the previous millennium. $\endgroup$ – David Hammen Feb 6 at 20:51

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