1. Good response.
2. So expendable SSME will be cheap? Cheapest core stage engine in the world?
Cheap compared with RS-25D, yes. Compared with Merlin 1D, probably not. But it's a very high-performance engine. Its cost should be roughly similar to that of a hypothetical regeneratively-cooled RS-68, and there should be a lot of commonality between the RS-25, RL-10 and J-2X lines.
As I recall, the cost of RL-10s shot way up when the Shuttle program closed down...
I think it's a waste of time and money to design SLS for 2 boosters just so you can use the old solids. Vehicles with more than 2 boosters are much more flexible. Maybe there's a reason why you can't have more if there is I don't know.
The rule is to use what you have. What we have is the nearly-finished 5-seg SRB. I'd personally have preferred AJAX (we also have the Atlas V CCB, even though they use Russian engines), but oh well. As I recall, Downix had an idea for using multiple boosters on a single attach point using a rack mount - bit of a waste of mass IMO, but for boosters that's less important, and I'm not sure how big the mass hit would actually be...
3. Going to Mars? Keep the dream alive I guess but not for a long long time after the law says the SLS needs to carry 130mt.
The law doesn't say anything about when
the 130 ton capability is supposed to be available. It just says that SLS has to be designed so that it can reach that number at some point. The only actual date given is for the 70-ton version.
4. Only launched manned on SLS? It is a manned capsule isn't it?
Yes, but now you've added a word. I said technically
, didn't I?
...Be aware that I have a totally baseless aversion to using smileys. It's a matter of honour...
Besides, what would you do with it on a different launcher? Send it to the ISS? Given that you already have SLS for BEO exploration and thus have to pay the fixed costs anyway, adding a core-only flight is cheaper than buying an EELV Heavy (as far as I can tell from currently-available numbers). And the hope is that we won't have to do that.
5. Yes this was for multiple launches 3-4 possibly. 1-2 makes for a more expensive SLS.
By my calculations, based on the Budget Integration document, the SLS program cost for one flight per year should be between $1.5B and $2B in modern dollars. That's the 130-ton version.
Adding a flight of the 70-ton version with iCPS (EDIT: iCPS inclusion has been questioned and is not positively certain) every year raises the price by $270M or so. Including the 21CGS costs (which are for more than just SLS) adds a little over $400M. (These costs don't all seem to inflate at the same rate; it's a bit of a confusing document.) The whole shebang, including Orion and its fixed costs, is under $4B in 2023 dollars, or between $2.4B and $3B in 2012 dollars.
Where are you getting your numbers?