.
Else we will be ceding the moon to China
Musk's Starship and Super Heavy Booster beat the SLS, I understand. Musk is well on the way to mass production of the Starship/Super Heavy Booster. They are expected to reduce the cost of launch to orbit by about 90%, or 99.8% from what it was 20 year ago.
What they need for a moon base is a way to refuel the Starship in orbit, and they are working on it.
StarShip (SS) the lunar version will not be ready until well after 2030.:
1. SS has to prove orbital refueling not just once, but repeatedly;
2. the Starship has to be man-rated ( usually a four year process );
3. the booster has to be man-rated as well; there is no crew escape mechanism for landing;
4. it will take at least 4 refuelings to get to the lunar orbiter - still in design stages;
5. there is no provision to refuel on the way back from the moon, there is no methane on the moon;
6. the delta-V on return from the moon is an order of magnitude higher than from LEO, and so the materials and the heat shield will have to be redesigned. The list goes on.
SLS, on the other hand, can do the job now in the short term with more cargo than lunar SS. If SLS is not fully funded, then there is no immediate replacement. Do you throw out something that works now in the hopes that something else, as yet unproven, will work at some unknown date in the future?
If SLS is cancelled,then the Chinese will be on the moon for years, perhaps a decade, before SS is ready.
More explanation here:
I loathe SLS! But if NASA and Elon Musk cancel it now, China will beat us to the Moon!
https://www.youtube.com/watch?v=nDXAfkdKKSk