Navigating after the apocalypse
November 15, 2013 4:34 PM Subscribe
If Earth-based command centers ceased functioning tomorrow, how long would the GPS system remain usable?
Imagine that a disaster of unprecedented scale—plague, nuclear holocaust, zombie apocalypse, whatever—has decimated humanity. There is no functioning electrical grid, or central government of any kind—only scattered pockets of survivors who are fending for daily survival. It's the world of Fallout or The Walking Dead.
But there are still handheld GPS devices lying around, and the batteries to power them.
How long would those GPS devices remain functional, with no one to monitor and manage the satellites? How long will it take for their power supplies to run down? Will they maintain a stable orbit on their own? If one of them suffers a system crash, will it reboot itself? If one or more of them does fail, how will that affect GPS users on the ground—will it simply render GPS inoperable for a particular geographic area? Basically, how long can Random Q. Survivor expect his scavenged GPS device to remain useful?
Imagine that a disaster of unprecedented scale—plague, nuclear holocaust, zombie apocalypse, whatever—has decimated humanity. There is no functioning electrical grid, or central government of any kind—only scattered pockets of survivors who are fending for daily survival. It's the world of Fallout or The Walking Dead.
But there are still handheld GPS devices lying around, and the batteries to power them.
How long would those GPS devices remain functional, with no one to monitor and manage the satellites? How long will it take for their power supplies to run down? Will they maintain a stable orbit on their own? If one of them suffers a system crash, will it reboot itself? If one or more of them does fail, how will that affect GPS users on the ground—will it simply render GPS inoperable for a particular geographic area? Basically, how long can Random Q. Survivor expect his scavenged GPS device to remain useful?
Best answer: It depends on your definition of "usable".
The problem is that the earth isn't a perfect sphere (or a perfect oblate spheroid). As satellites rotate, variations in local mass cause the orbits to drift. The control center for GPS issues commands to the satellites regularly to correct their orbits. If this doesn't happen, over time the system would become less and less accurate because the actual location of the satellite and where it says it is would increasingly diverge.
So it really depends on how much accuracy you need. If you can put up with more error, the system would be useful for longer.
posted by Chocolate Pickle at 4:53 PM on November 15, 2013
The problem is that the earth isn't a perfect sphere (or a perfect oblate spheroid). As satellites rotate, variations in local mass cause the orbits to drift. The control center for GPS issues commands to the satellites regularly to correct their orbits. If this doesn't happen, over time the system would become less and less accurate because the actual location of the satellite and where it says it is would increasingly diverge.
So it really depends on how much accuracy you need. If you can put up with more error, the system would be useful for longer.
posted by Chocolate Pickle at 4:53 PM on November 15, 2013
For one thing, if it was a nuclear holocaust the nuclear electromagnetic pulse would immediately disrupt many satellites and other electronic systems. Just casually Googling, this paper quotes a 2005 South Korean Defense Ministry journal saying that even U.S. military GPS and satellite communications capabilities would be disabled.
posted by XMLicious at 5:03 PM on November 15, 2013
posted by XMLicious at 5:03 PM on November 15, 2013
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posted by zsazsa at 4:51 PM on November 15, 2013 [3 favorites]