XYZ Coordinates to Earth Plot

Thx tony h.
I've update original post with the assumptions. Maybe I should have left any reference to Satellites out as I think solving this using the Pythagoras theorem and some other calculations in Excel is what 's needed. I could be very, very wrong; as you can tell, I'm lost.
I think it may be basic, what is the XYZ of a line intersecting a sphere; I know the radius of the earth and the total distance from 0,0,0 to the XYZ (of the Satellite). Don't know how to calculate the XYZ of the intersection.
I'm reading the pdf you indicated; trying to figure it out a bit.