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IOTL, the Hercules ASRM was a new design of solid rocket booster designed to completely replace the Morton Thiokol RSRM (the redesigned solid rocket motor, ie. the post-Challenger SRB design) for the Space Shuttle program. (details) It was canceled in 1993 after around a billion dollars were spent on the program, even though it offered higher ISP (about 10 seconds--a big deal!) and significantly higher (15,000 kN vs. 11,000 kN) thrust then the RSRM, and so would have allowed the Shuttle to carry larger payloads especially to the high-inclination orbits of Mir and the ISS. In the end, the Shuttle tank needed to be redesigned (the so-called Super LightWeight Tank, or SLWT) to allow the Shuttle to carry a useful payload to space station orbits.
So, suppose instead the ASRM is accepted for service, replacing the RSRM from some point in the mid/late-90s onward. What happens?