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The term suicide burn occasionally comes up in answers and comments, usually without any real explanation or definition.

What is meant by the term "suicide burn"?

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For a powered descent to the surface of a massive body like the Moon, it turns out to be most fuel efficient to do all your deceleration at the very end of the trajectory, right before impact.

(This is because if you decelerate sooner than that, you will be in flight longer; the longer you're up, the more fuel you need to spend counteracting gravity accelerating you toward the surface.)

So the fuel-optimum landing involves falling faster and faster toward the surface before doing your deceleration burn, which looks suicidal (and will be, if you don't leave sufficient margin for error).

Hence: suicide burn.

SpaceX's first-stage recovery is another example. In that case, suicide burn is a requirement, because even at minimum stable throttle, the engine produces more thrust than the weight of the stage, so it can't hold a constant low downward speed for any length of time; it has to time the burn so that it hits altitude zero just before it reaches velocity zero. SpaceX calls this maneuver "hover-slam".

I'm not sure of the origins of the term "suicide burn"; it's extremely popular in the Kerbal Space Program community. It doesn't appear in the Google books nGram viewer at all. It comes up in some SpaceX discussions but a lot of that looks like bleed from KSP.

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  • $\begingroup$ If you've seen Interstellar, I'm pretty sure they do a dramatic version of this when they land on Miller's planet. $\endgroup$
    – Ricky
    Commented Jul 28, 2015 at 23:54
  • $\begingroup$ The proper stackexchange term is suicide by-design. $\endgroup$
    – uhoh
    Commented May 2, 2017 at 20:02
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    $\begingroup$ Tidbit: Your most fuel efficient landing isn't falling like that, but rather you set your periapsis very, very low (the more thrust your engine puts out the lower your desired periapsis) and do your landing burn from orbit, a gravity turn in reverse. It's still a suicide burn, though. $\endgroup$
    – Loren Pechtel
    Commented Jun 24, 2017 at 20:45
  • $\begingroup$ @LorenPechtel It's the same thing: because you can't do the entire deceleration instantaneously, your near-horizontal initial approach turns into a near-vertical final. $\endgroup$
    – Russell Borogove
    Commented Nov 10, 2018 at 1:27
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    $\begingroup$ At least from my experience in KSP, no matter how efficiently you deorbit (which is certainly important as suggested), the principle remains that burning inside the atmosphere to decelerate when the craft is still moving faster than terminal velocity is wasteful if it is done any time other than the very last possible second. $\endgroup$
    – Darren
    Commented Oct 31, 2019 at 13:15

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