Why do spacecraft have to undergo such high temperatures during reentry? Is that basically to save on fuel? For example - to take the ridiculous extreme, suppose you performed a reentry burn of the same magnitude used to place the craft in orbit in the first place? As in you use something the size of the Saturn V, with it's attending appetite for fuel, to drop the craft's orbital speed from tens of thousands of miles per hour, down to hundreds of miles per hour, before it has the chance to drop into the atmosphere. Is that possible? Is it as fuel intensive as I'm making it out to be?