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I know... Elon Musk calls the redesign of the BFR "unintuitive". I'm just trying to get ahead of the Starship introduction and hop test presumably in March/April timeline.

But isn't it better to use proven retro-propulsive entry burn technique to get rid of excess speed and to keep the second stage from direct heat transfer with the atmosphere, rather than using the old idea of a heat shield and its horrendous track-record of causing catastrophes (I'm pointing out the space shuttle in particular)? Not to mention its awfully hard process of repairing and refurbishing the shuttle after each flight.

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    $\begingroup$ In over 300 crewed orbital flights, a heat shield failure has caused catastrophe exactly once, and as @NathanTuggy points out, Starship’s heat shield will be very unlike shuttle’s. $\endgroup$ – Russell Borogove Dec 25 '18 at 9:07
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    $\begingroup$ It will be capable of landing the same way as the Falcon 9 boosters - if it is used for sub-orbital flights. But that is a very unlikely scenario. $\endgroup$ – Everyday Astronaut Jan 25 at 22:02
  • $\begingroup$ Aren't heatshields a proven technique? $\endgroup$ – Sean Feb 4 at 6:14
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Falcon 9 reentry is only designed for first stages, with a reentry burn that is pretty minor - on the order of a few hundred meters/second. A second stage, reentering with far more velocity than a first stage, can't shed the extra velocity with a cheap burn, because the total delta-v necessary for that would be about as much as the second stage was capable of to begin with (4000-5000 m/s). Thanks to the rocket equation, that means the second stage would then have to be not merely twice as large, but much larger, probably at least five times the size than it would have been otherwise. And that in turn means the first stage needs to be that much larger.

In short, while propulsive reentry for a low-velocity suborbital stage is proven, propulsive reentry from orbit is known to not be a good idea.

Materials science has advanced quite a bit since the Shuttle was designed, and in particular, SpaceX has been experimenting with better, more robust heat shield designs for years. What's more, the Starship will have a much more favorable ballistic coefficient than the Shuttle did (since it will be much closer to empty), as well as a less demanding aerodynamic shape, making it easier to reenter with lower heat loads. So making the heat shielding reliably reusable without significant maintenance is likely to be quite achievable.

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  • $\begingroup$ In a recent video, Scott Manley noted that SpaceX appears to be switching to an entirely steel, regeneratively-cooled heatshield. He posits that the heatsink will be the (substantial) remaining onboard fuel. $\endgroup$ – Alex Hajnal Dec 26 '18 at 8:20

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