How large has to be the diameter of a telescope mounted to a satellite , traveling at an altitude of h=400 km , in order to resolve a tennis ball (d~10cm) ? Is it realistic?
What is approximately the best resolution of google earth?
I want to discuss widely over the problem.

Question

jamesj · Answer

What really matters more than diameter of the telescope is its focal length. The other you need to know is what is the smallest size image you can distinguish (e..g, $ 1 \mu m $ ). You might find this helpful on basic optics of cameras: http://www.youtube.com/watch?v=uhP3jrxraMk#!

jamesj · Answer

In this simple analysis, given 
X = width of object = 0.1 m
Z = distance of object = 400,000 m
x = minimum size of distinguishable object = 1 micrometer, for example,

you can solve for f.