The last two Artemis missions which use the shuttle-era RS-25D engines will fly in 2025 and 2026. Is there ever a possibility that, in the case that Aerojet Rocketdyne delivers their RS-25Es (or at least 4) early, that the RS-25Ds on the SLS will be swapped for the cheaper RS-25Es?

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    $\begingroup$ But isn't the higher cost of the RS-25D engines a sunk cost? If you swap them out, you're not going to use them for something else, so where is the savings? $\endgroup$ Mar 16, 2022 at 15:49
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    $\begingroup$ ... and it's not really clear how much cheaper they are. The original ones are claimed to be 40 million each, the new contract pays 100 million each. But without a date to take inflation into account that can't be compared. $\endgroup$
    – asdfex
    Mar 16, 2022 at 18:43


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