Link here. This is a long (4 parts) and detailed overview of the changing state of the SLS system and its future missions. As it notes right at the start,
NASA has started updating plans and schedules for additional SLS Block 1 launches in the early 2020s after Washington added federal budget money for a second Mobile Launcher (ML) platform and umbilical tower in late March.
Construction of a new Mobile Launcher frees the first ML from a three-year long downtime for teardown and reassembly after the first SLS launch of Exploration Mission-1 (EM-1), currently projected for mid-2020. Instead of being retired after one launch, the Block 1 configuration could fly multiple times.
With two mobile launches (costing almost a billion to build), NASA has more flexibility (assuming it gets full funding). It can now fly both the smaller Block 1 configuration of SLS multiple times without delaying the first launch of the planned more powerful Block 2 version expected to come later.
The article discusses in great detail the possible variations in design and scheduling for the first unmanned mission, the Europa mission, the first manned mission, and possible missions beyond, all of which are based on Congress’s continued blank check support for this very expensive and very questionable program.
Sadly, it increasingly appears that Congress is going to throw a lot of money at this program. SLS looks like it is going to fly several times, and maybe more. It will likely send Europa Clipper to Jupiter, and later astronauts on a stunt mission around the Moon. Later, the Washington cartel of big aerospace companies, NASA, Congress, and our international partners in Europe and Russia are gearing up to get LOP-G funded as well, with SLS the vehicle to launch and supply it.
All of this will cost a lot, take forever, and not make the future exploration of the solar system possible in the slightest. None of that matters however. Congress wants it, and Congress being corrupt and irresponsible is going to get it.