function x = plotpath3d( lat, long, tt, vt )
	Rearth = 6378.137e3;
	Rsat = Rearth + 850e3;
    
	dt = 0.1;
	T = 6117.7;
    
	[xb, yb, zb] = sph2cart( long*pi/180, lat*pi/180, Rearth );
	[xs, ys, zs] = sph2cart( -76*pi/180, 0, Rsat );
	
	phi = 0;
	
	for i=1:9001
		phi = phi + (dt/T) * (2*pi);
		xx(i) = sqrt( (xb-xs)^2 + (yb-ys)^2 + (zb-zs)^2 );
		[xs, ys, zs] = sph2cart( -76*pi/180, phi, Rsat );
	end
	
	% return the slope of the TCA
    x = (myslope(diff(xx).*(-10), 4380, 25)) - myslope(vt, 4380, 25);
