What satellites do

Television, internet, navigation, weather, farming, disasters and science — from orbit.

1. How does satellite TV reach your home? — A broadcaster beams channels up to a geostationary satellite, which sends them back down to millions of small dishes that point at one fixed spot in the sky.
2. What is a transponder on a satellite? — A transponder is the satellite's relay: it receives a signal from the ground, shifts it to a different frequency, amplifies it and sends it back down.
3. How do satellite phones and VSAT terminals work? — They skip mobile towers and cables: the phone or small dish talks straight to a satellite, which links it to the rest of the network.
4. How does satellite internet work? — Your dish sends data to a satellite, which relays it to a ground station connected to the internet; replies come back the same way.
5. What Is Starlink? — Starlink is a satellite internet constellation operated by SpaceX.
6. How does GPS find your position? — Your phone times radio signals from several satellites, turns each travel time into a distance, and works out the one point that fits all those distances.
7. Why does GPS need four satellites? — Three satellites fix your position in space, but your phone's clock is not perfect, so a fourth is needed to solve for the clock error too.
8. How is NavIC different from GPS? — GPS covers the whole world from about 20,200 km up; NavIC is India's own regional system, covering India and about 1,500 km beyond from geosynchronous orbit.
9. What is GAGAN? — GAGAN is India's system that corrects GPS errors for aircraft, broadcasting corrections from geostationary satellites so planes can navigate more accurately and safely.
10. Does your phone use NavIC? — Many newer phones can receive NavIC alongside GPS and other systems, but only inside NavIC's coverage area of India and about 1,500 km around it.
11. Why do navigation satellites use two frequencies like L1 and L5? — The ionosphere slows radio signals by an amount that depends on frequency, so comparing two frequencies lets a receiver measure and remove that error.
12. How do weather satellites see clouds? — They photograph sunlight reflected by clouds in daytime and measure the heat clouds give off at all hours, using several wavelengths at once.
13. What is the difference between an imager and a sounder? — An imager takes pictures of clouds and the surface; a sounder measures how temperature and moisture change with height, layer by layer through the atmosphere.
14. How do satellites track cyclones? — Weather satellites watch a cyclone's clouds day and night, and forecasters read the cloud pattern and cloud-top temperatures to estimate its position and strength.
15. How do satellites help watch the monsoon? — Satellites measure clouds, moisture, temperature and winds over the land and oceans around India, filling the gaps between ground stations that forecasts depend on.
16. What is the difference between optical and radar satellites? — Optical satellites photograph sunlight reflected from the ground; radar satellites send out their own microwave pulses, so they can see at night and through clouds.
17. What does satellite image resolution mean? — Spatial resolution is the size of the smallest patch of ground one pixel represents; a 5.8 m camera shows far more detail than a 56 m one.
18. What are swath and revisit time? — Swath is the width of the strip a satellite images as it passes; revisit time is how long it takes to image the same place again.
19. How does radar (SAR) see through clouds? — Synthetic aperture radar sends long-wavelength microwaves that pass through clouds, and combines echoes along its path to act like a giant antenna.
20. How do satellites help farmers? — Satellites map which crops are growing where, how healthy they are and how dry the land is, so India can forecast harvests and respond early to drought.
21. How do satellites help during disasters? — Satellites warn of storms before they hit, map floods and damage afterwards, and keep communication working when ground networks fail.
22. How do satellites help fishermen find fish? — Satellites measure sea temperature and ocean colour; INCOIS uses these to mark likely fishing zones and sends daily advisories to India's coastal communities.
23. How do satellites measure the ocean? — Satellites bounce radar off the sea to measure its height, read its temperature and colour, and gauge surface winds, covering oceans that ships rarely visit.
24. Why put telescopes in orbit? — Earth's atmosphere blurs starlight and blocks X-rays completely, so telescopes above it see sharper images and light that never reaches the ground.