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I was told that the new SLS that NASA is building is using the same SRBs that the space shuttle used just with one extra segment added. Five instead of the original four.

If the shuttle had used these larger SRBs what would that do for its capabilities?

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Five-segment boosters for shuttle were being actively developed prior to the STS-107 failure.

enter image description here

(personal notes)

The paper Five-Segment RSRB Feasibility Status (1999) predicts an increase in ISS payload capabilty to 40,000 lbm (baseline capability was ~ 35,000 lbm)

That is nice, but by far the best improvement would have been the almost complete elimination of Return to Launch Site (RTLS) aborts for performance problems1. With the use of Space Shuttle Main Engine throttle setting of 109%, the system would have the capability of performing Trans-Atlantic Abort (TAL) off the pad and gaining Abort-to-Orbit capability before SRB separation. With higher throttle settings, ATO could be achieved off the pad.

enter image description here

(the image reproduction was poor, I attempted to restore the color coding)

Space Shuttle Five Segment Booster Short Course (2002)

Achieving Space Shuttle ATO using the Five-Segment Booster (2003)

The STS-107 failure would lead to the end of the shuttle program and the closeout of most shuttle upgrades, including the five segment booster for shuttle. Some of that work would live on for SLS.

Note: The boosters aren't the "same SRBs that the space shuttle used" exactly though even discounting the additional segment:

enter image description here

https://www.nasaspaceflight.com/2021/07/srbs-from-shuttle-to-sls/

1The potential for RTLS's due to system problems as defined in the flight rules would still exist.

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    $\begingroup$ It looks like the tradeoff for (mostly) eliminating the need for RTLS abort would have been several more seconds of SRB burn time, a period when no type of abort was possible. The 2001 (2003?) document states that it would have been 130 seconds, compared to a typical 125 seconds for Shuttle. Although the 1999 document seems to indicate 139 second burn time with five segments, at least as I am able to decipher since page 9 of that document is difficult to read. Presumably in later designs they changed the grain shape for more thrust resulting in less burn time. $\endgroup$ Commented Dec 18, 2023 at 20:04
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    $\begingroup$ @StevePemberton agree on the burn time. Thanks for the correction on the document year, I have an older local copy of what looks like the same basic paper (AIAA-2001-3413) but I linked to the newer one, I'll fix. Unfortunately the repro quality is just as bad. $\endgroup$ Commented Dec 18, 2023 at 20:28
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    $\begingroup$ Thanks for the very detailed answer! It is interesting to know that they were thinking about it over 20 years ago. $\endgroup$
    – Burgi
    Commented Dec 19, 2023 at 9:38
  • $\begingroup$ What unit does "lbm" refer to and how does it differ from "lb"? $\endgroup$
    – Dan Mašek
    Commented Dec 20, 2023 at 13:12
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    $\begingroup$ @DanMašek scienceworld.wolfram.com/physics/Pound-Mass.html $\endgroup$ Commented Dec 20, 2023 at 13:25

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