
So Who Will Build a GPS Backup? - peburns
https://medium.com/@patburns/so-who-will-build-a-gps-backup-337eca7c3b8b
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howard941
Russia, China, the EU, and India. Is this a trick question?

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davismwfl
Those are not a backup to the US GPS. Each of those Countries are building a
positional system that is mostly subjected to the same type of interference
and spoofing as the US GPS system. They may have some military components to
their systems which are more hardened, but the consumer version doubtfully
would. Not to mention I am sure they would have a similar component to reduce
accuracy for non-military in case of an "emergency" as they see it (no
different than the US). The reason there are many combo chips/systems that
support 2-3 of these separate systems is the frequencies are very similar or
identical in some cases, so again, same types of issues could be found.

We used to run the LORAN(-C) in the US for positional accuracy in near shore
waters. Of course it wasn't nearly as good as GPS but it was a nice backup,
but that system was shutdown around 2010.

As for true backups there is a celestial navigation system that has been in
use for a long time in military aviation which is quite accurate. That is not
a system that can be spoofed from what I know, but it is subjected to other
issues which could be hard to overcome for land/sea based navigation.

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peburns
LORAN would be easy but it appears the USG doesn't want to fund it. It's still
unidirectional and could suffer similar spoofing attacks as GPS, though this
seems less likely. This article describes a sort of bi-directional LORAN
alternative that would support encryption and uses inexpensive OTS components.

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davismwfl
Yea, the reference in the article is what made me think of when we used LORAN
out on the ocean. I learned to navigate the ocean using only a compass and
LORAN, which while imperfect was always good enough to get us where we were
going. I think a system like LORAN could be revisited with some encryption and
not take a huge investment, the only problem is I am not sure the cost would
be worth it given the likely limited range to being near coastal only. Doesn't
solve the problem of crossing an ocean and wanting solid, reliable positional
accuracy for emergencies etc.

