The Global Positioning System is a global satellite navigation system created and maintained by the United States. The Galileo project is a European Union global satellite navigation system serving the same role.
Questions tagged [gps]
77 questions
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Why does GPS depend on relativity?
I am reading A Brief History of Time by Stephen Hawking, and in it he mentions that without compensating for relativity, GPS devices would be out by miles. Why is this? (I am not sure which relativity he means as I am several chapters ahead now and…
Thomas O
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How was the first atomic clock calibrated?
As we all know, atomic clocks are being used to measure time and the GPS system.
But I was wondering based on what was the first atomic clock calibrated and how accurate this calibration was based on our standards nowadays?
MichaelScott
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Why isn't the GPS location calculated from the Schwarzschild metric?
The GPS uses the flat space light propagation formula to calculate the distance from the source (the satellite) to the receiver (observer on Earth):
$$ d=c \cdot \Delta t$$
where $c$ is the speed of light in Minkowski vacuum, $\Delta t$ is the…
label
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Why don't we put satellites into an orbit where there is (almost) no time dilation/contraction compared to Earth's surface?
Consider:
On this image, if I understand correctly, the time dilation diagram is shown depending on the height for circular orbits. First in low orbit, time slows down relative to the surface due to high speed, but for higher orbits, speed and…
12
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What are the real-life applications of General Relativity?
As we all know, the most famous application of GR and SR is the GPS guidance system, where time dilation can be corrected. But it seemed that everywhere I go, GPS is the only answer to how GR can be used in real life, and to me sounds kind of sad.…
JY _Decipherer_
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Cancelling special & general relativistic effects
We know that for a GPS we need to make a correction for both general and special relativity: general relativity predicts that clocks go slower in a higher gravitational field (the clock aboard a GPS satellite moves faster than a clock down on…
10
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Why do GPS satellites care about Earth clock at all? (relativity)
Many online resources make grandiose claims about how GPS would be useless without relativistic corrections.
Specifically, they outline that satellite clocks runs slower by 7μs/day due to special relativistic effects as the satellites are moving at…
obadz
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How does time dilation affect the synchronization of clocks in different gravitational potentials?
How does time dilation affect the synchronization of clocks in different gravitational potentials, as described by the general theory of relativity?
For example if we consider two clocks, one located at sea level and another at a high altitude…
Michael Yoannou
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Special Relativistic approximation to GR
Some time ago I was talking to a professor in college about some of the fundamental aspects and origin of General Relativity. I was surprised to learn, in fact, that a pretty good approximation to GR can be achieved simply by using Special…
Noldorin
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That 10km/day error predicted if GPS satellite clocks not corrected for relativity
Some authorities have stated publicly and without explanation that if the theories of Special and General Relativity were not taken into account in the design of the GPS (by building the satellite clocks to run 38us/day slower than GPS time before…
surd100
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I don't see that general relativity is really needed for GPS to work correctly
From what I understand, GPS localization is based on the difference in the reception time from the time of emission of a signal from different GPS satellites whose positions are known. For this we need very precisely synchronized clocks in the…
doetoe
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"Earth spinning faster will break GPS and atomic clocks".. Umm, how?
Since it's just come out that Earth is apparently spinning about a milliscecond and a half faster.. I see a bunch of "articles" claiming this will.. somehow.. break atomic clocks and make GPS useless.. (Google "earth spinning faster break atomic…
Jim Witte
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How are GPS corrected for special/general relativity?
I was looking for the equations that are used by the GPS receiver to calculate its position and time correction (bias). By looking at the Navigation Equations on Wikipedia, I don't see any account for special or general relativity in the equations.…
mhmhsh
- 93
6
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4 answers
Why GPS is at LEO?
Why GPS/GLONASS/Galileo satellites are on low earth orbit?
Why geostationary orbit is so bad? Sattelites might be placed there 'statically' and more precise...
The only problem I can see is navigation close to poles, but they have this problem…
BarsMonster
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Gravitational resonances for satellites
I read on the website of European Space Agency that the altitude of Galileo satellites, which is 29600 Km from the center of the Earth, is chosen to avoid gravitational resonances so that station keeping manoeuvres are not needed during the lifetime…
newzad
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