Question: Mechanics. Trajectory Plot

I am fairly new to Maple and trying to understand the dsolve command for numerical solutions and plotting graphs of radial distances and trajectory plots.
This is my code below. All of it successfully brings up a solution apart from the very last command and I don't understand why it is not working. 
I believe the last plot is plotting a trajectory plot but I am not sure. I am meant to use the solution to plot the trajectory plot (X(t),Y9t))=(r(t)cos(theta(t)),r(t)sin(theta(t))) in the (XY) plane and plot the function H(t)=1/2 (dr/dt)^2+1/2 r(t)^2 (dtheta/dt)^2-k/r(t) against t. :S

DifferentialSystem := {r(t)*(diff(theta(t), `$`(t, 2)))+2*(diff(r(t), t))*(diff(theta(t), t)) = 0, diff(r(t), `$`(t, 2))-r(t)*(diff(theta(t), t))^2 = -1000/r(t)^2, r(0) = sqrt(65), theta(0) = arccos(1/(sqrt(65))), (D(r))(0) = 4*sqrt(65)*(1/13), (D(theta))(0) = -6/13};


nops(soln(0)); op(2,soln(0)); nops(op(2,soln(0))); op(2,op(2,soln(0))); op(2,op(3,soln(0))); op(2,op(4,soln(0))); op(2, op(5,soln(0)));

for k from 0 to 1000 do X[k]:=op(2,op(2,soln(k*0.01))) od:

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