Not sure actually - maybe we would have arrived at what SpaceX is doing (reusable rockets and space capsules) earlier? As for the RS-25, it's used in the SLS m

Not sure actually - maybe we would have arrived at what SpaceX is doing (reusable rockets and space capsules) earlier? As for the RS-25, it's used in the SLS mostly because NASA still has left-over engines from the Shuttle program in storage, otherwise it wouldn't make sense to use an engine designed for reusability on a single-use rocket. According to https://en.wikipedia.org/wiki/RS-25#Space_Launch_System https://en.wikipedia.org/wiki/RS-25#Space_Launch_System, "Once the remaining RS-25Ds are exhausted, they are to be replaced with a cheaper, expendable version designated the RS-25E".