SpaceX is swiftly moving toward achieving its ultimate goal of rapid reusability: flying a single booster twice within a 24-hour time period. It’s a goal that Elon Musk says SpaceX will achieve later this year—but in order to make good on that promise, the company must first say goodbye to its hardest-working rocket yet. That would be the full thrust Falcon, known to SpaceX followers as the Block 4.

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