Comment on If a mysterious force secretly changed EVERY clock worldwide one minute forward, how long would it take until people notice, and how would people/governments react?

• Rivalarrival@lemmy.today ⁨1⁩ ⁨day⁩ ago

  The GPS almanac is a table of the exact orbital information of every satellite. Every receiver needs a copy of the almanac to understand where the satellites are supposed to be, so that it can determine where it is in relation to those satellites.

  When their clocks all shift one minute simultaneously, the almanac isn’t updated. Every satellite is 60 seconds away from where the almanac says it should be.

  If the satellites were geostationary, receivers would still work, they’d just be off by 0.25 degrees of longitude as the entire constellation would be shifted the same amount. But the GPS constellation consists of satellites in a variety of inclined orbits. Nothing is where the almanac thinks it is, and nothing is where it is supposed to be in relation to anything else.

  Parent comment is correct: GPS will immediately fail, and remain down until an updated almanac is published and distributed.

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  • lordnikon@lemmy.world ⁨23⁩ ⁨hours⁩ ago

    Interesting so I guess they update the almanac when a leep second is preformed

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    • DankOfAmerica@reddthat.com ⁨22⁩ ⁨hours⁩ ago

      No, the almanac accounts for the leap second since it was created. It doesn’t need to be updated.

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    • davidgro@lemmy.world ⁨20⁩ ⁨hours⁩ ago

      The GPS ‘time zone’ does not account for leap seconds at all and is currently 18 seconds ahead of UTC. The GPS navigation messages from the satellites do however include the current offset.

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• Deceptichum@quokk.au ⁨23⁩ ⁨hours⁩ ago

  Satellites aren’t world wide, they’re world orbiting.

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