1. The gravity of the earth on the satellite provides the centripetal force of the satellite's circular motion, and an equation can be established, in which, in general, the gravity can be approximately equal to the gravity of the satellite, the radius of the circular motion is the height above the ground plus radius of the earth, and the period is known and can be solved.
2. The area of the circular corona surrounded by the tangent from the satellite to the earth's surface.
3. Find the arc length corresponding to the longest chord of the circular crown in 2, and then compare it with the circumference of the earth. Like three? The remaining area can be calculated.