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As far as I can tell, the terms Suicide burn and Hoverslam have both been invented rather recently (with SpaceX themselves coining Hoverslam and the Kerbal Space Program community loosely credited with Suicide burn) but I'm unsure the exact accepted definition. I've come across two variants/definitions and I'm unsure which is right:

  1. Suicide burn and Hoverslam are synonyms where Hoverslam was coined by SpaceX to prevent PR problems/negative connotations when describing the Falcon 9 landing procedure.
  2. Suicide burn indicates a manuever before vertical landing where the engine is run at 100 percent throttle timed exactly so that the rocket's velocity reaches zero when it reaches the ground (and thus reaches a theoretical max efficiency ) while in a Hoverslam the engine is not throttled to 100 percent and instead operates at a lower power level for a longer time and has the ability to increase or decrease throttle, thus making landing easier (and more inefficient).

Which is right? Are both wrong?

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    $\begingroup$ Neither term was ever introduced with a precise definition, so I don’t feel the question is meaningful. $\endgroup$ Commented Nov 14, 2019 at 16:18
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    $\begingroup$ a hoverslam is a suicide burn with a little bit of wriggle room? $\endgroup$
    – user20636
    Commented Nov 14, 2019 at 18:43
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    $\begingroup$ @RussellBorogove I think the question is meaningful. If the terms were never introduced with precise definition and are approximately equivalent, then that is the answer. $\endgroup$
    – Ingolifs
    Commented Nov 14, 2019 at 19:10
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    $\begingroup$ +1 for effectively citing KSP. $\endgroup$
    – miltonb
    Commented Nov 16, 2019 at 21:16
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    $\begingroup$ I think Suicide Burn can be used to describe maneuvers other than surface landings. For example, a suicide burn could be used to match velocities and get very close before a docking. The definition should be this: a suicide burn is a maneuver that uses maximum thrust with minimal room for error. $\endgroup$ Commented Nov 18, 2019 at 6:13

2 Answers 2

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I would say there's one substantial difference:

Suicide burns are normally a matter of choice, you light your rocket as late as possible to save fuel.

The Falcon 9, however, has no choice in this matter. The rocket is incapable of being throttled low enough to hover. Once the landing burn begins you can play with the thrust a bit to determine the exact point where the rocket will come to zero velocity, but you must get it right on the first try, there is no go around.

I strongly suspect they coined the new term because they didn't like "suicide burn", though.

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Hoverslam is the same thing as Suicide Burn. Just sounds less suicidal.

The engine does not run full throttle during Hoverslam/Suicide Burn. The engine power is adjusted constantly to account for the change of speed vector, distance, etc. However, to save fuel, the engine was burned as close to 100% as possible. It is a very dangerous procedure because at this stage with so little fuel left, the rocket was so light yet the engine was so powerful that even at the lowest output the engine is still powerful enough to send the rocket back into the sky.

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