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  • $\begingroup$ Would you think (also based on speculative reasoning, you have more of a handle on it than me) that this angle would/should be maintained through the entire first stage ascent? Would it make sense to stop the angle after max-Q or at a specific point of ascent? $\endgroup$ Commented Sep 17, 2018 at 19:35
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    $\begingroup$ @MagicOctopusUrn I believe the engines on the Long March 3 boosters are only tangentially gimbaled (as pointed out in comments above), so the outward angle is maintained for the entire booster burn. Ditto any fixed-nozzle solid boosters. Gimbaled booster engines might be mounted so that their neutral position is canted outward like this, but during nominal flight they could steer directly aft to claw back the cosine loss. $\endgroup$ Commented Sep 17, 2018 at 19:45
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    $\begingroup$ Adding some speculation to yours: If you lose a strap-on booster early, the mission is over, catastrophically, so who cares about preventing a yaw moment then? I'll bet that they aim the strap-on's thrust through near where the expected COM is at burnout, because that's where preventing an unexpected yaw moment (from slightly early burnout on one side) could save the mission. $\endgroup$ Commented Sep 17, 2018 at 20:55
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    $\begingroup$ @WayneConrad Loss of a single strap-on booster isn't necessarily a loss-of-vehicle/loss-of-mission situation, particularly with a liquid booster, and particularly if it's not too early in the burn. A number of launches have lost an engine on ascent and continued on to partial or full success (e.g. AS-101, Apollo 6, Apollo 13, Falcon 9 CRS-1). If a booster failure causes a large yaw moment, though, it will be a loss-of-vehicle situation. $\endgroup$ Commented Sep 17, 2018 at 21:59
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    $\begingroup$ I was incorrect about the gimbaling; it's the core engines that swivel tangentially, and the booster engines are fixed-position. The angle looks to be about 5º, which cosine is 0.996 -- implying less than half a percent wasted thrust from the boosters. $\endgroup$ Commented Aug 19, 2021 at 5:08