Are there any NASA engineers that can explain to me why the SLS program is a good idea (from a financial standpoint) It doesn't seem feasible to spend more money on refurbishing an engine than designing/building a new one. For example it costs around $35 mil to refurbish 1 rs-25 engine in order to be flown on the SLS (and will only be flown once) Whereas spacex' raptor engine costs less than $1mil to manufacture and theoretically will be flown up to 1000 times. I've been puzzled by this for years.