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Comment by vardump | Hacker News Reader

So my phone can use these satellite navigation systems: U.S. GPS, Russian GLONASS, European Galileo, Chinese BeiDou and Japanese QZSS.

I guess one more doesn't hurt, huh?

It's curious how major powers all want to have their own satellite navigation systems.

Edit: QZSS is a regional system, and not due to start until November 2018, yet my phone detected one of those satellites earlier about 2-3 weeks ago. Interesting, especially considering I'm nowhere near Japan. Unless, of course, it was a bug or some weird error case. Or maybe QZSS was doing some early testing?

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These are essential national security assets, used for military purposes, and which a hostile (or even neutral) owner could turn off in case of war. The civilian use-case is a handy side benefit.

Was a handy side-benefit, then GPS got so cheap and ubiquitous people tag their dogs and hire bikes. Now, location services are an essential civilian service.

But that's not the reason why all these countries feel the need to launch their own. If that was what India cared about they'd happily stick to GPS.

Just because someone tags their dog doesn't make it an essential civilian service.

A number of devices are theorized to use GPS for cryptographic randomness, such as ATMs. In 2007 the US navy accidentally jammed San Diego's GPS signal, but the effect wasn't too huge.

https://fieldlogix.com/news/navy-accidentally-jammed-gps-sys...

I've listened to interviews with the creators of GPS and they were very clear that it was always intended as a dual use military / civilian system.

It's always been that way, I mean, the master gps control station is a very highly guarded USAF base in Colorado.

If you build your missiles to work using gps (as another poster pointed out), then you also want those to work if the US decides to not let you use the gps system.

> ...my phone detected one of those satellites earlier about 2-3 weeks ago. Interesting, especially considering I'm nowhere near Japan.

Could be an error, but you could just be in Australia or just about anywhere on the Eastern hemisphere. The orbits are geosynchronous and thus very high.

https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System#...

Definitely not geosynchronous. It is a Quasi-Zenith Satellite System as per your link.

A lovely animation of three satellites: https://upload.wikimedia.org/wikipedia/commons/b/ba/Qzss-01-...

https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System#...

"QZSS uses three satellites, each 120° apart, in highly inclined, slightly elliptical, geosynchronous orbits. Because of this inclination, they are not geostationary; they do not remain in the same place in the sky. Instead, their ground traces are asymmetrical figure-8 patterns (analemmas), designed to ensure that one is almost directly overhead (elevation 60° or more) over Japan at all times."

Ahhhh: geosynchronous versus geostationary. I hope I wasn't the only confused muppet!

That animation clearly shows they are geosynchronous?

How can you tell which nav systems your phone can see?

Android API provides this:

https://developer.android.com/reference/android/location/Gns...

You can also use apps like GPS Test [0], etc. They can tell it as well. QZSS is represented by square icon(s) in that app.

[0]: https://play.google.com/store/apps/details?id=com.chartcross... (not affiliated with them in any way)

QZSS has been in test phase since 2010, and has had a full constellation of 4 satellites since last year.

I don't think IRNSS covers regions outside South Asia.

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