Q.Explain in detail the geostationary and polar satellites.

Step 1. Deriving the geostationary height. Setting the orbital period $T$ equal to 24 hours (86400 s) in $T^2=(4\pi^2/GM_e)(R_e+h)^3$ and solving for $h$ gives an altitude of about 36,000 km above the equator.

Step 2. Why it appears stationary. A satellite placed there, orbiting in the plane of the equator, completes exactly one orbit in the same time the Earth completes one rotation about its own axis -- so, viewed from a fixed point on the ground, the satellite never appears to move across the sky; it hangs "stationary" overhead.

Step 3. Geostationary use case. This makes such satellites ideal for continuous communication links and broadcasting to a fixed ground antenna, since the antenna never needs to track a moving satellite; India's INSAT group of satellites are geostationary satellites of exactly this kind.

Step 4. Polar satellites. These orbit at a much lower altitude, typically 500-800 km, with their orbital plane passing over the North and South poles rather than the equator, giving a much shorter period of roughly 100 minutes -- many orbits per day. …

Derive the geostationary height from T = 24 hours, then contrast it with the lower, faster polar …

• Mixing up which orbit is higher (geostationary) versus lower (polar). …