Q1Satellite Communication
Question
Q.1. What are the different orbits employed in satellite communication and what are their applications?
Answer
Satellite orbits are classified as LEO (160-2000km, low latency, used for imaging/broadband constellations), MEO (2000-35786km, used for GNSS navigation), GEO (35786km, fixed position, used for broadcast/communication/weather), and highly elliptical orbits like Molniya (used for high-latitude coverage).
Satellites are placed in different orbits depending on their intended application, each offering a distinct trade-off between coverage area, signal latency, ground-station complexity, and the number of satellites needed for continuous service.
Low Earth Orbit (LEO): altitude roughly 160-2000 km, characterized by short orbital periods (about 90 minutes to 2 hours) and very low signal propagation delay (a few milliseconds), but each satellite covers only a small ground footprint and remains visible from a given location for only a short period, requiring large constellations (tens to thousands of satellites) for continuous coverage. Applications: earth observation/remote sensing imaging (requiring close proximity for high resolution), low-latency broadband internet constellations (e.g., Starlink, OneWeb), and some scientific/research satellites.
Medium Earth Orbit (MEO): altitude roughly 2,000 km up to just below GEO altitude, offering a balance between coverage area and latency; a constellation of a few dozen MEO satellites can provide global coverage. Applications: Global Navigation Satellite Systems (GPS, GLONASS, Galileo, NavIC), which require precise, continuously available multi-satellite visibility for triangulation-based positioning.
Geostationary Earth Orbit (GEO): altitude 35,786 km directly above the equator, with an orbital period exactly matching Earth's sidereal rotation period, causing the satellite to appear stationary relative to a fixed point on Earth. Applications: television broadcasting, fixed satellite communication services, weather monitoring (continuous observation of the same region), since a fixed-pointing ground antenna can maintain a continuous link without tracking, at the cost of higher signal latency (~240 ms round trip) and reduced coverage of polar regions.
Highly Elliptical Orbit (HEO), e.g., Molniya orbit: a highly eccentric orbit with a low perigee and very high apogee, spending most of its orbital period near apogee over a specific region (typically high-latitude/polar regions poorly served by GEO satellites, which appear low on the horizon or below it at extreme latitudes). Applications: communication and broadcasting services for high-latitude regions (notably used historically by Russia for coverage of its far-northern territories), where GEO satellite visibility/elevation angle would otherwise be too poor for reliable service.