Written primarily to define the area of the earth covered by a narrow-beam antenna carried on a synchronous satellite in circular, near equatorial orbits, a computer program has been developed that computes the locus of intersection of a quadric cone and a sphere. The program, which outputs a list of the longitude and latitude coordinates of the locus of intersection and a plot of the locus, is presented and described in several sections in this paper: first, a mathematical analysis of the problem is offered; next, a section on usage describes inputs and outputs; and finally, some typical examples are presented. A program listing is appended. See also EM 010 450. (Author/SH)