Not to mention that the giant flying fuel tank (er... 'rocket') is _substantially_ lighter now that you've burned most of the fuel off.
Re:SpaceX Grasshopper Flies High
by InclinedPlane on Tuesday April 23, 2013 @12:28PM
(#5596121)
And separated from the 2nd stage and the payload, of course.
Two other points to consider:
Atmosphere is slowing you down as you go up as well, so lift off requires fighting that as well. Therefore the energy you've expended is not entirely stored in potential energy. (Fun fact: If it weren't for the atmosphere, rockets would actually take off almost horizontally. They go up at first to get out of the thickest air before going sideways.)
The craft is much lighter, because it no longer has the payload, and also has used almost all of its fuel.
Re:SpaceX Grasshopper Flies High
by Florin_Andrei on Tuesday April 23, 2013 @05:50PM
(#5598223)
> I imagine there's a lot less fuel required to land than is required to take off.
Right.
At take off, the delta vee is the escape velocity PLUS all the losses due to friction, which are tremendous.
At landing, the delta vee is only equal to terminal velocity. EDIT: Okay, plus some flying time on top of the landing point.
Upon landing, the atmosphere does most of the slowing-down for you, so you only need enough fuel to reduce the speed from terminal velocity (not sure what this would be for a rocket, probably several hundred miles an hour, at least) to 0. So, I'm sure it's not an insubstantial amount of fuel, but maybe less than you'd think?