In other words, what caused SpaceX to miscalculate the amount of propellant required to safely land the booster. They had landed successfully on the drone ship in April. So what went wrong here? What was different?
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5$\begingroup$ If this is the mishap I'm thinking of, they miscalculated how much TEA-TEB the rocket would need to restart the engines during reentry and landing. There was enough propellant, but not enough of this pyrophoric chemical they use to start the engines. Not making this an answer because my memory is so bad that this might be entirely made up. $\endgroup$– Wayne ConradMar 15 at 21:13
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2$\begingroup$ It seems to be that they actually ran out of propellant popularmechanics.com/space/rockets/a21389/… @WayneConrad $\endgroup$– Starship - On StrikeMar 15 at 21:47
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1$\begingroup$ I'm glad I added that disclaimer then. $\endgroup$– Wayne ConradMar 15 at 21:56
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5$\begingroup$ "liquid oxygen fuel", ugh $\endgroup$– Organic MarbleMar 15 at 21:59
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7$\begingroup$ @OrganicMarble "liquid oxygen fuel" is a special kind of LOX that you have to use with "RP1 oxidizer". $\endgroup$– Wayne ConradMar 15 at 22:05
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When performing a propulsive landing, the harder you accelerate, the less speed you pick up from gravity, and the less fuel you need.
Falcon 9 flight 26 was intended to perform a three-engine landing burn. According to an Elon Musk tweet, one of the engines wasn't operating at the intended power level. This reduced the acceleration and increased the fuel needed: although the booster had enough fuel to perform a three-engine landing, it didn't have enough for a two-and-a-half-engine landing.
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$\begingroup$ @OrganicMarble, "fuel" translates as "things that make the engines run". $\endgroup$– MarkMay 23 at 0:29
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$\begingroup$ Ah, so fuel is also "electricity". Got it. $\endgroup$ May 23 at 0:30
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$\begingroup$ @OrganicMarble, for something like Rocket Lab's Electron rockets, yes. I'm fairly sure that the Falcon 9 uses a gas-generator turbopump instead. $\endgroup$– MarkMay 23 at 0:59
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1$\begingroup$ Your Elon Musk tweet is from a day before the one that says it ran out of oxygen. I think his opinions changed as SpaceX investigated the crash. $\endgroup$ May 23 at 11:42
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3$\begingroup$ I, for one, find the pedantry and associated refusal to accommodate very entertaining. $\endgroup$ May 23 at 12:03