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I was looking at engine bells, and I was wondering: would it be possible or useful for a diamond shaped engine bell, that would stage sections off, creating a wider bell as the rocket leaves the atmosphere? Would this be any benefit for SSTO vehicles?

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  • $\begingroup$ I'm having a hard time visualizing what you mean. $\endgroup$ – Hobbes Aug 10 '18 at 18:23
  • $\begingroup$ The Vinci engine was at one time intended to have a telescoping nozzle to get the effect you mean (larger nozzle), but that would be extended before firing the engine. spaceflightnow.com/news/n1406/17airbussafran/vinci_400266.jpg $\endgroup$ – Hobbes Aug 10 '18 at 18:24
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    $\begingroup$ @Hobbes - a nozzle expanding from throat to a vacuum-appropriate-diameter, at which point there would be a separation line, beyond which it would narrow back down to a sea-level-appropriate diameter. The question is, would the reconstriction ruin the performance of the engine. $\endgroup$ – Russell Borogove Aug 10 '18 at 19:09
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    $\begingroup$ @OrganicMarble Much less weight in machinery carried in the final high-expansion configuration. $\endgroup$ – Russell Borogove Aug 11 '18 at 16:43
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    $\begingroup$ Ah, so basically adding a 2nd converging section. That would decelerate the exhaust so there would be Isp losses. Cooling the 2nd converging section would be interesting too. I guess the question is, would the performance loss due to exhaust velocity loss be greater than the gain from matching the exit plane pressure. My gut says this isn't a good idea. $\endgroup$ – Organic Marble Aug 11 '18 at 17:18

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