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China's version of GPS now has more satellites than US original

asia.nikkei.com

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Re: China's version of GPS now has more satellites than US original

#41

Post by dragonelite »

Maakuth wrote: post #19

Isn't the proliferation of multiple GNSS constellations actually quite positive thing? The smartphone geolocation chips seem to have no problem receiving signals from all constellations. So effectively this competition between the systems allows for denser coverage of location satellites. This in turn should enable more accuracy and faster location acquisition even with limited sky visibility. In security sense, it s…

In a perfect world yeah, but given the geopolitical and geoeconomical changes going on. The tradewar to seperate the Chimerica relationship, you probably want to own your own navigation systems.

Re: China's version of GPS now has more satellites than US original

#42

Post by onethought »

credit_guy wrote: post #38

So, if North Korea wants to develop an ICBM, the main challenges are 4: take off (which they appear to have mastered), miniaturization of the bomb, navigation and reentry vehicle. All the remaining 3 are quite difficult, and navigation in particular was traditionally done by a mix of inertial (i.e. based on gyroscopes) and celestial (i.e. based on the observation of stars). GPS makes all this unnecessary. If NK uses…

Is this just conjecture? It seems ridiculous that the US would rely on the fact they can control GPS satellites as form of missile defence... So shooting down their GPS satellites would also hamper there ability to launch ICBMs? Seems equally unbelievable.

Re: China's version of GPS now has more satellites than US original

#43

Post by willis936 »

londons_explore wrote: post #33
willis936 wrote: post #9

Earlier quoted context omitted.

With military receivers (or codeless phase tracking) the current constellation is good down to centimeters.

This isn't possible without third party data. Things like the refractive index of the atmosphere (which depends on weather patterns), and the fact orbits are slightly warped due to varying gravitational fields and radiation pressure from the sun, all add up to location innacuracies unless you can correct for these effects. That correction requires data, which needs to come from a third party because the satellites do…

Correct, if only L1 is used. However as GPS exists today receivers can track phase variations between L1 and L2 without the codes necessary to decode the signal on L2.

Re: China's version of GPS now has more satellites than US original

#44

Post by dragonelite »

vinay427 wrote: post #36
ddalex wrote: post #32

Earlier quoted context omitted.

the problem with just one is that US will insist having a deadswitch on it, just like it did with Galileo. so you must have your own if you don't want US to have a Damocles sword over you

Newer GPS satellites apparently don't support selective availability, so they would have no way of preventing access to only civilian devices. Of course, any of these systems can be jammed or shot down but that would affect anyone using it. > In September 2007, the U.S. government announced its decision to procure the future generation of GPS satellites, known as GPS III, without the SA feature. Doing this will make…

Why would a reformist country like China and Russia trust such a thing. We were also told that mass surveillance was a conspiracy/nutjob story, but the Snowden leaks has shown us a different world.

Re: China's version of GPS now has more satellites than US original

#45

Post by raihansaputra »

dragonsh wrote: post #28
ksec wrote: post #17

Earlier quoted context omitted.

Something SpaceX could consider? Given their ambition with Satellite Internet backbone.

Yeah hopefully there can be a consortium of Automobile manufacturers, internet companies and academia which can launch such a constellation of open source satellites for location services. Hopefully that can be combined with terrestrial peer to peer network to make sure it works even if military or specific nation wants to block it.

IATA would also be a suitable member. All civilian aircraft still rely on the unencrypted part of these GNSS systems AFAIK.

Re: China's version of GPS now has more satellites than US original

#46

Post by Spare_account »

vinay427 wrote: post #36
ddalex wrote: post #32

Earlier quoted context omitted.

the problem with just one is that US will insist having a deadswitch on it, just like it did with Galileo. so you must have your own if you don't want US to have a Damocles sword over you

Newer GPS satellites apparently don't support selective availability, so they would have no way of preventing access to only civilian devices. Of course, any of these systems can be jammed or shot down but that would affect anyone using it. > In September 2007, the U.S. government announced its decision to procure the future generation of GPS satellites, known as GPS III, without the SA feature. Doing this will make…

If I wanted my neighbours to trust my GPS system more, I'd tell them I don't have selective availability.

Re: China's version of GPS now has more satellites than US original

#48

Post by raihansaputra »

credit_guy wrote: post #38

So, if North Korea wants to develop an ICBM, the main challenges are 4: take off (which they appear to have mastered), miniaturization of the bomb, navigation and reentry vehicle. All the remaining 3 are quite difficult, and navigation in particular was traditionally done by a mix of inertial (i.e. based on gyroscopes) and celestial (i.e. based on the observation of stars). GPS makes all this unnecessary. If NK uses…

The unencrypted GPS automatically disables themselves when they detect speeds of a missile to prevent exactly this.

Re: China's version of GPS now has more satellites than US original

#50

Post by dragonelite »

londons_explore wrote: post #33
willis936 wrote: post #9

Earlier quoted context omitted.

With military receivers (or codeless phase tracking) the current constellation is good down to centimeters.

This isn't possible without third party data. Things like the refractive index of the atmosphere (which depends on weather patterns), and the fact orbits are slightly warped due to varying gravitational fields and radiation pressure from the sun, all add up to location innacuracies unless you can correct for these effects. That correction requires data, which needs to come from a third party because the satellites do…

Groundbased gps transmitters might help to increase accuracy.
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