I assume that the Gravitational Force Equation isn't Pe = M g Δh then because when I type "gravitational potential energy" into a search engine that's what appears! And that always assumes constant g.
To do this I'm given a graph showing gravity reducing non-linearly from 3.7 N/kg at the surface to 0.7 N/kg at 8 x 10^6m. I believe that the equation for a fixed gravitaional pull is E = M x G x H - however with changing gravity as the object rises - how do you calculate this?