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Given the dangers of the massive heat generated during re-entry, why can't spacecraft simply slow down using thrusters (or whatever) and just come in gently?


marked as duplicate by Nathan Tuggy, Hohmannfan, ForgeMonkey, David Hammen, GdD Apr 12 '16 at 9:11

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  • $\begingroup$ The original booster gave the spacecraft its orbital velocity. Wouldn't you need an identical booster to remove that same velocity? $\endgroup$ – DJohnM Apr 12 '16 at 16:20

Because propellant is extremely costly in orbit (as of now). As long as you have to bring up every gram from earths gravity well, you want your tanks to be as empty as possible before re-entry. Aerobraking is currently the only way to get rid of speed without relying on costly propellant.

That being said, things might change if propellant would already exist in-orbit and was relatively cheap to acquire. In that case it might be more sensible to re-fuel (re-propell?) before descent.

  • $\begingroup$ To illustrate how expensive it is to boost propellant to space: Suppose you developed a rocket that could burn money with a performance similar to current space-stable propellants. If NASA could go to the Bank of Space and withdraw piles of dollar bills to stuff in the engine they would do so--it would be cheaper than bringing fuel up from Earth. $\endgroup$ – Loren Pechtel Apr 13 '16 at 1:00

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