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The Space Shuttle and the Starship need tiles for termal Protection while reentry.

Why Falcon 9 doesnt need them?

Joe Jobs
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2 Answers2

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The Falcon 9 booster never goes to orbit, so it is muuuuuuuuuuuch slower. It doesn't even go to space. (I.e. it doesn't cross the Kármán line.) If the Falcon 9 upper stage were to reenter, it would need some form of heat shield.

In fact, the complexities of having the upper stage survive reentry is precisely why SpaceX gave up on the idea of reusing the upper stage.

Jörg W Mittag
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    Isnt it possible to fire the engines to slow down the 2nd stage? Would it consume too much fuel? – Joe Jobs Oct 13 '20 at 20:16
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    You need as much fuel to slow down as you need to speed up. Except you need much more because you also need to carry extra fuel to speed up the extra fuel you carry to slow down. Plus, a significant amount of the acceleration is provided by the first stage, so you also need to carry fuel to cancel out the velocity that the first stage provided. And you need to carry extra fuel to accelerate that extra fuel you carry. The heat shield is also heavy, so you need to add extra fuel to accelerate the heat shield. And extra fuel to accelerate the extra fuel for the heat shield. – Jörg W Mittag Oct 13 '20 at 20:19
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It is the first stage of Falcon 9 returning from a suborbital flight with much less than orbital speed, about 2.8 km/s and 80 km altitude.

The Space Shuttle returned from a real orbit at much higher speed, about 8 km/s and 400 km high.

2.8 times the speed means 8 times the kinetic energy.

Uwe
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