Why GPS Needs Einstein: Satellite Clocks Run Fast #Shorts
Pack: 05 - Why GPS Needs Einstein Satellite Clocks Run Fast
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Every GPS fix on your phone depends on Einstein's relativity.
- GPS satellites fly about 20,200 km (12,550 miles) up and circle Earth twice a day (GPS.gov).
- In weaker gravity, their atomic clocks gain about 45 microseconds a day; their orbital speed slows them by about 7. Net: about 38 microseconds a day fast (NIST).
- Left uncorrected, position errors would build up by roughly 10 km a day (Richard Pogge, Ohio State University).
- The fix: satellite clocks get a "factory frequency offset" on the ground so they tick slightly slow before launch. NTS-2, launched in 1977 with the first cesium clock in orbit, measured the effect within about 1% of the prediction (Neil Ashby, Living Reviews in Relativity, 2003).
Did you know your phone depends on relativity?
Sources
- NIST, "Putting Einstein to the Test"
- N. Ashby, "Relativity in the Global Positioning System," Living Reviews in Relativity (2003)
- R. Pogge, Ohio State University, "Real-World Relativity: The GPS Navigation System"
- GPS.gov, "Space Segment"
- NASA Science, "10 Things Einstein Got Right"
Images
- "GPS-IIRM.jpg", U.S. government, public domain
- "Einstein 1921 by F Schmutzer - restoration.jpg", Ferdinand Schmutzer (restoration by Adam Cuerden), public domain
- Clock diagram: drawn by USASIHQ from NIST and Ashby (2003) figures.
- "Global Navigation Satellite System (GNSS) Satellite Fleet (SVS5627 - gnss 02 usa 00001).jpg", NASA Scientific Visualization Studio, public domain
- "Navigation Technology Satellite – II.jpg", U.S. Naval Research Laboratory, public domain
_Satellite_Fleet_(SVS5627_-_gnss_02_usa_00001).jpg){kind=link}
