Expert: Philip Stahl - 9/5/2009

Question
what is the escape velocity of a space ship from earth going to outer space? and what is the terminal velocity of space ship from outer space going to down to earth?

Answer
Hello,

Technically speaking, there is no single escape velocity, since it will differ according to the altitude from which the ship sets off. (In future space missions, this will become extremely critical, and it is virtually a foregone conclusion that no manned craft will be leaving from the surface of Earth-  but rather from a platform already in space - for which v_e will be much less.)

Anyway, you are probably referring to the *surface escape velocity* which is just under 7 miles per second, or about 25,000 mph. This is the velocity a ship would need to escape the full Earth's gravity.


As for "terminal velocity" there is no specific value I know of, in terms of a space ship arriving at or near Earth. Again, terminal velocity will depend on the specific altitude for which one is terminating a mission. (E.g. it may be a docking hookup at a space station or platform)

In addition, IF the ship is actually to land on the *surface* of Earth, then it is clear that the aimed for terminal velocity will simply be 0 m/s! In practice, this will probably vary from around 1- 4 m/s depending on the retro-thrusting rocket effects etc.

Bear in mind here that a space craft is presumed to be under powered flight, at least for a major segment of its re-entry. It is not going to simply drop like a falling object (e.g. rock) for which the term "terminal velocity" is really applicable, since it includes the effects of atmospheric drag as counterbalancing a "free fall" under gravity.