Question

The minimum number of satellites needed to be placed for world-wide communication between any two locations on earth’s surface is:
A) $6$
B) $4$
C) $3$
D) $5$

Answer 1

This question is linked to the property of triangles. Here, we need three points to construct a triangle (a closed figure), the points can be shown as satellites. Hence by constructing a triangle out of the $3$ satellites, we can cover the whole earth.

Complete step by step answer:
A satellite is an object in space that orbits or circles around a bigger object. There are two kinds of satellites: natural (such as the moon orbiting the Earth) or artificial (such as the International Space Station orbiting the Earth). There are dozens upon dozens of natural satellites in the solar system, with almost every planet having at least one moon. Saturn, for example, has at least $53$ natural satellites, and between $2004$ and $2017$ , it also had an artificial one — the Cassini spacecraft, which explored the ringed planet and its moons. Today, a growing number of satellites orbit around the Earth, making various Earth observation, communication, navigation and science applications possible. While we may not always realize or acknowledge their existence, the important role these systems play in our daily lives cannot be underestimated. They contribute considerably to our well-being and enable us to achieve our objectives in new and innovative ways. As technology advances, the potential of satellites will undoubtedly continue to grow. New markets will emerge along with new opportunities to push the boundaries of what space technology currently offers.
In this question, the satellites will act as three vertices of a triangle. For a world-wide communication between any two locations of the earth, minimum $3$ satellites must be placed such that each pair of the satellites subtend angle of ${120^ \circ }$ at the centre of earth.
So, the correct answer is C) $3$ .

Additional Information:
Artificial satellites, however, did not become a reality until the mid- $20th$ century. The first artificial satellite was Sputnik, a Russian beach-ball-size space probe that lifted off on Oct. $4,1957$ . That act shocked much of the western world, as it was believed the Soviets did not have the capability to send satellites into space.

Note:
Here we need to understand that the minimum number of satellites required to be placed for world-wide communication between any two points on the earth’s surface is more dependent on the geometry than science. Further in this question we need to have a good understanding of the concept of triangle.