Sigh-Fi

I get the feeling that calculating a space shift perfectly for a long enough time jump so that one would appear exactly on the surface of planet Earth (not more that a meter or two above and definitelly not at all below) would probably be extremely hard giving the precision required and how gravitation works: theoretically every single body in the Universe affects the position of planet Earth and each other, and whilst the effect of gravity drops steeply with distance, over enough time the errors of not having calculated using all bodies add up, which for very precise positioning (not merelly "near planet Earth" but actually above but not too high a certain point in its surface) would probably get dangerous fast.

So I bet that if we ever do time travel it will only really work for really small timeframes (forget about going back a couple of million Earth orbits to the time of the dinossaurs) or it will both have a space shift and a time shift with a vehicle capable of at least limited space flight and reentry so that a "near planet Earth" error margin is acceptable in the spacial shifting part.

This is, of course, before we go into the whole time paradox discussion.

PS: I was curious so looked for and found a paper about the influences Earth's orbit. One of the interesting conclusions one can derive from it is having to take in account the collision with the asteroid that killed the dinossaurs if one wanted to travel back in time to the time of the dinossaurs with a suitable space shift to end up on the Earth's surface.