why is atmosphere reentry such an issue? If it is just because of speed hitting the atmosphere why can’t the spacecraft just slow down before and synchronise with earth rotation?
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Heat is kinetic energy; hitting air fast enough is indistinguishable from hitting hot air. And hitting the atmosphere *is* how it slows down.
> can’t the spacecraft just slow down before [hitting the atmosphere]
By burning fuel? The exponential nature of the rocket equation; it would take about 10x as much fuel to reach a speed and then get back to zero (if you can’t refuel inbetween) as just reaching that speed. Rockets are already 90+ percent fuel, [almost all of which goes towards accelerating to the ludicrously fast speeds involved](https://what-if.xkcd.com/58/).
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