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My question is

How long is a Falcon 9 suicide burn?

I assume the answer might vary between rides, depending on the payload lifted and its destination orbit so the time might not be the same for a drone ship land or a landing on the start. But I am just looking for an orientative figure. If it varies one or two seconds its not important for me.

In addition, How many engines are used in the suicide burn?

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  • $\begingroup$ The payload is irrelevant as it's no longer attached. I believe the orbit is also irrelevant as that velocity has been shed in the reentry burn. $\endgroup$ – Loren Pechtel Feb 5 at 2:13
  • $\begingroup$ The payload might not be irrelevant, since the initial propellant loaded might vary and the one consumed in the ascent will surely vary. All in all, the rocket to land and its initial data when starting the landing burn (mass or velocity) might vary susbtancially between missions. $\endgroup$ – Tintin Feb 5 at 9:17
  • $\begingroup$ I'd argue that the F9 technically does not do a suicide burn because there is still throttling in the engine. A proper suicide burn is maximally efficient and thus only uses its engines for the minimum time at maximum thrust, which F9 does not do. "Hoverslam" is more appropriate imo $\endgroup$ – Dragongeek Feb 6 at 0:28
  • $\begingroup$ @Tintin All of that is long passed by the time of the landing burn. There's no point in bringing extra fuel back to Earth, they will have on board only what they need for landing plus a suitable safety margin. $\endgroup$ – Loren Pechtel Feb 6 at 1:13
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I think their preferred term is "Hover slam" not suicide burn.

This is somewhat answered in a different question:Boostback, reentry, and landing burn times and it is about 32 seconds.

We saw on the NRO mission, where they asked SpaceX not to show fairing deploy or any video from the second stage (Spooks, whatcha gonna do?) that they played the reentry as the main view and showed the altitude/speed gauges for the landing first stage.

From memory, the atmospheric drag slowed the booster down to about 2000Km/h and then the landing burn took care of the rest. Was very interesting to watch how much the reentry and landing burns accomplished in terms of speed.

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  • $\begingroup$ 32 seconds? Wow, so it really depends on launchs. I have been searching on the videos and its seems that some landings only need a 17 secs burn. You can see here that the ones from Falcon heavy are 17 secs youtu.be/l5I8jaMsHYk?t=86 Even Falcon 9 can have 17 seconds: in todays video we can see a light on the ocean around 17 secs before landing, also agreeing with the commentator youtu.be/fe6HBw1y6bA?t=1322 $\endgroup$ – Tintin Feb 4 at 14:49
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    $\begingroup$ I think you are correct it really depends on the mission and parameters. We know that while a Cargo Dragon to ISS can RTLS, they cannot on the Crew missions due to different launch profiles and staging points. $\endgroup$ – geoffc Feb 4 at 15:13
  • $\begingroup$ @geoffc: Cargo Dragon cannot RTLS. Dragon could, but the last flight of the original Dragon was CRS-20. Starting from CRS-21, they are only flying the Crew Dragon derived Cargo Dragon, which is too heavy for an RTLS landing. $\endgroup$ – Jörg W Mittag Feb 5 at 7:15
  • $\begingroup$ @JörgWMittag Fair point. I meant the original Dragon missions with Cargo. We need better naming for this stuff. $\endgroup$ – geoffc Feb 5 at 11:42
  • $\begingroup$ I tried to look up what SpaceX calls it, but the original Dragon seems to have vanished from their website. They only talk about Cargo Dragon, which is the Crew Dragon derived-one, Crew Dragon, and Dragon by which they sometimes mean Crew Dragon, and sometimes the family consisting of both Crew and Cargo Dragon. $\endgroup$ – Jörg W Mittag Feb 5 at 19:38

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