clear; close all
%
%  Time to orbit earth as a function of altitude
%
%  Principles from physics:
%       Angular acceleration must = grav accel
%       Angular accel = omega^2 * r
%       Grav accel is a function of altitude
%
r_earth = 6000;     %% Radius of earth, km
alt = 600;          %% altitude, km
g_surf = 9.81;      %% accel of gravity at surface
r_alt = r_earth + alt;
g_alt = g_surf*(r_earth/r_alt)^2;
r_altm = 1000*r_alt; %% change km to m
%
%  Solve omega^2 * r = g
%
omega = sqrt(g_alt/r_altm); %% rad per sec
rpsec = omega/(2*pi);       %% rev per sec
rphr = rpsec*3600;          %% rev per hr
trev = 1/rphr               %% hr per rev
v = omega*r_alt             %% speed, km/sec