The SLS block 2 is planned to have advanced boosters. What type of boosters are these and how much thrust will those produce?

  • $\begingroup$ Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. $\endgroup$
    – Community Bot
    Dec 9, 2023 at 10:30
  • 2
    $\begingroup$ I'm voting to reopen--though the OP could've done a better job, the planned SRBs for SLS Block 2 are the BOLE upgrade, as seen in this Space SE answer. You have to drill a little to realize it, but I think the question's actually 100% unambiguous, and the details requested aren't actually present in the answer I linked to. $\endgroup$
    – Erin Anne
    Dec 9, 2023 at 20:51

1 Answer 1


The SLS Block 2 booster upgrade is the Booster Obsolescence and Life Extension (BOLE) for Space Launch System (SLS) (Tobias, Griffin, McMillin, Haws, Fuller, 2019), which

  • introduces new composite casings
  • upgrades the propellant to HTPB from PBAN
  • changes the nozzle and insulation for these upgrades
  • electric thrust vector control
  • a simplified systems tunnel, among other structural simplifications like combining the nosecone and frustum

Per section 6 of the linked document, the BOLE upgrade is predicted to add three metric tons of additional TLI performance. Unfortunately, the thrust profile in that document is limited to a badly-compressed graph with poorly-labeled axes they use as their Figure 4. Figure 4 from the linked document, showing improved Vacuum Thrust versus Burn Time for the BOLEs versus the current SLS Shuttle-derived boosters, with a broadly similar profile except for upward-ramping thrust for an early portion of the flight where the current SLS booster's thrust is flat

This since-404'd SLS Overview from NASA indicates a vehicle takeoff thrust of 9.5 million lbf; it's a little unclear to me how much of that is provided by the RS-25s in the core stage, but it seems likely to be either the 109% or 113% power levels as summarized by Wikipedia. For the sake of approximation we'll use the 109% power level (420,000 lbf) times four engines: $$ (9.5*10^6 \text{lbf}- 4*4.2*10^5 \text{lbf}) / 2 \approx 3.9*10^6 \text{lbf per booster} $$

That result compares favorably to the 3.28 million lbf sea-level thrust per current SLS booster quoted by Wikipedia, though I don't see that figure in any of the nearby sources.

Being SRBs, there's significant variation in thrust through the burn profile (see the figure reproduced from the first link) so it's not clear to me what the maximum thrust from the BOLE SRBs will be, or if that's actually intended to occur post-liftoff (I can't imagine why that would be! the stack is heaviest at liftoff!), but that's at least a preliminary number to work from.


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