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How long is the first stage of a landing Falcon 9 remain hypersonic, and under control of its grid fins? Specifically the hypersonic component is of interest.

(Future second question will be, based on 6 attempts so far with grid fins, has SpaceX exceeded the record for controlled hypersonic flight yet?)

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Addressing the "has SpaceX exceeded the record" part of the question:

This graph shows that a Space Shuttle reentry was in the hypersonic flight regime for approximately 25 minutes. (I took 1.7 km/s ~ Mach 5 ~ end of hypersonic regime).

enter image description here

I'm pretty sure that's longer than the entire flight time for a recovered Falcon 9 first stage.

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The F9 first stage remains hypersonic until only shortly before landing - this is evidenced by the sonic boom emitted shortly before landing as it transitions to subsonic speed probably less than 10 seconds before landing.

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    $\begingroup$ This may or may not be true (I don't know), but keep in mind that there is something in between subsonic and hypersonic, namely non-hypersonic supersonic. Borrowing from Wikipedia: In aerodynamics, a hypersonic speed is one that is highly supersonic. Since the 1970s, the term has generally been assumed to refer to speeds of Mach 5 and above. en.wikipedia.org/wiki/Hypersonic_speed $\endgroup$
    – user
    Commented Jan 8, 2017 at 12:10

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