Question: Polar plots for two differential equations

Hi,

I have two differential equations describing a solar sail in 2D.

One is my radial direction and one is the tangential direction.

I have plotted r(t) and theta(t) but I want r(theta) so I have assigned my two differential equations and initial conditions, have my two plots for r and theta in terms of t and then I have used the following command to plot in polar coordinates:

and my final result doesn't give the theta values that I want.

Can anyone help?