Why GPS Needs 4 Satellites: India's Missing Fourth Clock

Why GPS needs 4 satellites, and why three can put your dot in a river. This 3D explainer shows how GPS works, why the fourth satellite isn't a spare or just for height, and how a cheap clock inside your phone's GPS chip gets caught. It also tells the story of India's NavIC: designed with seven satellites, down to three that could help find a position, and the launch of NVS-03 on 30 October 2026. In this video: How a GPS satellite turns time into distance Why three satellites should work on paper How a satellite can be alive but useless for finding you Why clocks in orbit tick at a different rate, and the 1977 test The four unknowns: across, along, up and time What NavIC was missing Chapters: 0:00 The dot in the river 0:20 Meera stops: your first guess 0:45 Late means far: how GPS measures distance 1:23 Why three satellites should be enough 2:03 NavIC and the dead clocks 3:02 Why clocks in orbit run fast 3:40 The 1977 measurement 4:15 The liar in your pocket 5:06 The fourth satellite: four unknowns 5:53 What NavIC was missing Status when published (1 November 2026): NVS-03 has launched and is raising its orbit. It isn't in service yet, and no service date has been given. Meera and the river are a fictional illustration, not a real NavIC event. Maps, satellites and scenes are illustrations, not to scale. Sources: GPS space segment: https://www.gps.gov/space-segment How GPS works (MathWorks): https://www.mathworks.com/help/satcom... Relativity and GPS (Ashby, Physics Today, 2002): https://physicstoday.aip.org/features... Error analysis for GPS: https://en.wikipedia.org/wiki/Error_a... NavIC standalone gap (Business Today, 30 Jul 2026): https://www.businesstoday.in/india/st... NVS-03 launch (Business Today, 31 Oct 2026): https://www.businesstoday.in/india/st... NVS-03 first orbit raising (Deccan Chronicle): https://deccanchronicle.com/southern-... The launch (The Week, 30 Oct 2026): https://www.theweek.in/news/sci-tech/... IRNSS-1F clock (Inside GNSS): https://insidegnss.com/?p=196593 IRNSS-1A: https://en.wikipedia.org/wiki/IRNSS-1A NavIC: https://en.wikipedia.org/wiki/Indian_... If this helped, like, share it with a curious friend, and subscribe for more animated science. Narration: AI voice. Animation: made in code. #GPS #NavIC #ISRO #NVS03 #HowGPSWorks #Satellites #AtomicClock #Relativity #Science #India