Calculating Satellite Aperture Radius

[k3r0]

Homework Statement

Estimate (in the order of magnitude) the size of a satellite lens (aperture radius) required to resolve a human face at the surface of the Earth if the satellite is orbiting at an altitude of 100km. Assume λ to be 600nm.

Homework Equations

θ = 1.22 (λ/D)

The Attempt at a Solution

I feel like this should be a really simple problem but I've been struggling with it for a while now. I want to find D, but I don't have the angular resolution, θ, either. Should I estimate it? There's another equation, θ = (h/D)k but it still has D in it. I also can't figure out how to take into account the altitude distance. If someone could help me out it'd be much appreciated.

 

[gneill]

You'll have to estimate the required angular resolution given the satellite distance and a typical head