An interesting comment here introduced me to the concept of Thrust-augmented Nozzles aka Afterburning Rocket Engines. The pubs I've read on it so far introduce the concept as a way to provide good performance throughout ascent. The nozzle performance is enhanced at low altitudes by engaging the afterburner at ignition, possibly turning it off later at altitude.
This kind of sounds like a good idea, but all the pubs I've see so far are from the originators of the idea, and as far as I know, it's never been adopted. (F-1s dumped the gas generator exhaust into the nozzle - it was fuel-rich so presumably burned, but that's not the same thing at all).
What are the downsides to this concept? (I mean, besides the obvious "the benefit wasn't worth the cost", but why?)
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