Q.Write a short note on polar satellites.

Since a satellite's orbital period depends only on its orbital height (via Kepler's third law), choosing the height carefully lets engineers design satellites for very different purposes.

Geostationary satellites. Setting the orbital period to exactly $24$ hours and solving $T^2=(4\pi^2/GM_e)(R_e+h)^3$ for $h$ gives an altitude of about $36{,}000\ \text{km}$ above the equator. A satellite placed there, orbiting in the plane of the equator, completes one orbit in exactly the time it takes the Earth to complete one rotation -- so, as seen from the ground, it appears to hang motionless over one fixed spot on Earth. This makes geostationary satellites ideal for continuous telecommunication and broadcast links to a fixed ground station; India's INSAT series are geostationary satellites of exactly this kind. …