I was just reading an article on the Space Shuttle Columbia tragedy and I began to wonder, why do they need to re-enter the atmosphere at roughly 17,000mph? Why not slow down to a less “burn up on re-entry” speed?
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With space being a vacuum there are very few molecules for the shuttle to pass by and therefore virtually no friction, meaning the shuttle can’t slow down on its own the way a car would if you lift off the gas or an aeroplane would if its engines cut out (Newton’s First Law). The only way to actually adjust its speed is through its engines (either forward or reverse) pushing out exhaust gas (Newton’s Third Law).
Because the shuttle uses almost all its fuel to escape Earth’s atmosphere in the first place, it doesn’t have any way of slowing itself down, instead it allows friction to do the job for it on re-entry to the atmosphere. This means, though, that it will still have roughly the same speed with which it left the atmosphere in the first place.
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