Timeline for answer to Are side boosters sometimes angled even if they are symmetrically arranged? by Anthony X
Current License: CC BY-SA 4.0
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| when toggle format | what | by | license | comment | |
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| Aug 19, 2021 at 5:08 | comment | added | Russell Borogove | 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. | |
| Nov 27, 2019 at 23:43 | comment | added | David Hammen | @Erik - I agree. It's much more likely that this is something else entirely, such as reducing plume-plume interactions. | |
| Nov 27, 2019 at 7:22 | comment | added | Erik | I can't refute this speculative answer, but it seems like an expensive precaution for a likely catastrophic problem. Seems like the cosine loses would be significant. | |
| Oct 25, 2018 at 17:11 | vote | accept | CommunityBot | moved from User.Id=12102 by developer User.Id=47211 | |
| Sep 17, 2018 at 23:03 | comment | added | Russell Borogove | @WayneConrad The question is about Long March 3, which uses liquid-fuel boosters (an early failure would leave you carrying propellant you couldn't burn, which would likely endanger the mission; a late failure might not, especially if upper stages had performance margin available). As for solids, you're probably right for 99% of cases -- but I can conceive of cases where a defective solid loses significant power without immediately exploding. In no case, however, would adding a big pitch/yaw moment to the situation improve things :) | |
| Sep 17, 2018 at 22:49 | comment | added | Wayne Conrad | @RussellBorogove If you lose an engine in a multi-engine liquid stage, the remaining engines can continue to burn the fuel intended for the lost engine: you lose thrust, but you don't lose delta-V (I think). But if you lose a strap-on solid motor, you're not getting anything out of its fuel anymore. Now it's just weight. Plus, how do you lose a strap-on solid motor in a benign way? Don't they tend to burn until they either burn out more or less normally, or stop in some way that ruins your day? | |
| Sep 17, 2018 at 21:59 | comment | added | Russell Borogove | @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. | |
| Sep 17, 2018 at 20:55 | comment | added | Wayne Conrad | 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. | |
| Sep 17, 2018 at 19:45 | comment | added | Russell Borogove | @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. | |
| Sep 17, 2018 at 19:35 | comment | added | Magic Octopus Urn | 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? | |
| Sep 17, 2018 at 19:24 | history | answered | Anthony X | CC BY-SA 4.0 |