The Space Transportation System (STS) could bring a fully loaded shuttle orbiter of 109 tons to orbit (or maybe empty+payload 68+25=93 tons). The Space Launch System (SLS) Block I is based on STS, but is said to be able to lift only two thirds to three quarters of that, 70 tons, to LEO. I would have thought that the SLS instead would be more powerful than the shuttle's launch stack.
SLS has an added fifth segment in its solid boosters and four instead of three of the same main engines. Also, it will have an upper stage with 26 tons of fuel compared with the smaller orbital maneuvering system of the shuttle. The thrust is greater for the SLS on each of the stages. So what does all the extra power go to? If the vague mass-to-LEO measure is useless here, what would a good comparative bottom line measure of their capabilities be? Could SLS Block I carry a fully loaded shuttle orbiter if it could be attached to it?
Solid booster (same isp 269 sec):
STS 15,000 kN
SLS 16,000 kN (+6%)
First stage (same isp 452 sec vacuum):
STS 5,250 kN
SLS 7,440 kN (+40%)
Upper stages OMS versus ICPS:
STS 2x27 kN and isp 316 sec
SLS 110 kN and isp 462 sec