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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

#31

Post by raihansaputra »

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…

The US is able to block GPS signal to a specific area (I think it was done on the Gulf War) or disable the unencrypted GPS signal (only the US military can decode them). I assume each system has the same capability too. The worst case scenario would be all parties decided to block the unencrypted portion and leaving all civilians to be location-blind, including civilian aircrafts.

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

#32

Post by ddalex »

gandalfian wrote: post #26
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…

Everyone sharing one system is excellent. Everyone sharing four increasingly redundant systems starts to look like a waste of money. We need a carpooling equivalent gps system. Still better than more bombs I guess.

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

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

#33

Post by londons_explore »

willis936 wrote: post #9
Gustomaximus wrote: post #3

Earlier quoted context omitted.

In the article the say accuracy is coming down to 1m vs 3-5 for other GPS

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 don't transmit it.

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

#34

Post by tialaramex »

Gupie wrote: post #21
lolc wrote: post #7

> When using BeiDou for car navigation, the receiver could theoretically transmit the car's location to a satellite in orbit, said Dean Cheng, a senior research fellow at the Heritage Foundation in Washington. Details on this? What does "theoretically" mean? Are there known protocols for this? Implementations? A lot of things could "theoretically" be done but aren't in practice.

Might be referring to their proposed Search and Rescue features, SAR.

COSPAS SARSAT rides along on new GNSS (GPS-like) birds from several nations because it's a good place to put it. They move in the sky (which means a beacon without its own ability to determine location can be triangulated using the doppler effect, not possible from a Geostationary communications satellite), there are lots of them, and they cover the whole Earth (the weather sats used for COSPAS SARSAT today are focused on areas where people care most about the weather, rather than aiming for global coverage...)

The COSPAS SARSAT beacons run at a different frequency to GNSS, they emit bursts of digital data at 406 MHz when active, containing a unique ID for the beacon, optionally (if fitted) its own estimate of its location, and some other data. A global database maps unique IDs to owner/ operators and the nearest rescue agency will try to figure out if this is a genuine alert (e.g. phoning your emergency contact "Hi, is Gupie out on their yacht today? I see, and how many are with them?") and then deploy appropriate resources.

Beacons are entirely passive until you activate them, and then you really want absolutely anybody to know where you are because you want rescuing. "Privacy" feels like a distant problem if you are currently in a leaking raft a hundred miles out to sea or just broke your leg half way up a mountain.

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

#35

Post by Barrin92 »

gandalfian wrote: post #26
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…

Everyone sharing one system is excellent. Everyone sharing four increasingly redundant systems starts to look like a waste of money. We need a carpooling equivalent gps system. Still better than more bombs I guess.

>Everyone sharing four increasingly redundant systems starts to look like a waste of money

straight out of the "having two kidneys is a waste of energy" school of thought

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

#36

Post by vinay427 »

ddalex wrote: post #32
gandalfian wrote: post #26

Earlier quoted context omitted.

Everyone sharing one system is excellent. Everyone sharing four increasingly redundant systems starts to look like a waste of money. We need a carpooling equivalent gps system. Still better than more bombs I guess.

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 the policy decision of 2000 permanent and eliminate a source of uncertainty in GPS performance that had been of concern to civil GPS users worldwide.

https://www.gps.gov/systems/gps/modernization/sa/

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

#37

Post by throw0101a »

Given that BeiDou-3 MEO has a different orbital altitude (21500km) than GPS (20500km) and thus different orbital characteristics, wouldn't a different number of satellites be needed?

I'm not sure that the number of satellites is that significant, and simply reflects design needs/constraints.

Ran across a good lecture series on GNSS a while ago going into more detail than most people care about ("3.3 - From Keplerian parameters to Earth centered Earth fied ECEF frame"). Module 6.7 - BeiDou:

* https://www.youtube.com/watch?v=Rpx1ySCKO3Q

Playlist:

* https://www.youtube.com/playlist?list=PLGvhNIiu1ubyEOJga50LJ...

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

#38

Post by credit_guy »

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 US GPS, there are most likely countermeasures in place, for example if the US detects an NK ICBM launch, then it stops or perturbs the GPS signal.

New providers of GPS complicate this problem.

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

#39

Post by gandalfian »

Barrin92 wrote: post #35
gandalfian wrote: post #26

Earlier quoted context omitted.

Everyone sharing one system is excellent. Everyone sharing four increasingly redundant systems starts to look like a waste of money. We need a carpooling equivalent gps system. Still better than more bombs I guess.

>Everyone sharing four increasingly redundant systems starts to look like a waste of money straight out of the "having two kidneys is a waste of energy" school of thought

You could buy yourself a dialysis machine "just in case" but you will have to give up something else to afford it. There is a trade off.

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

#40

Post by yoz-y »

ksec wrote: post #17
dragonsh wrote: post #15

Wouldn't it be nice instead of countries an open academic agency launch a series of open source satellites for locations. Hopefully likes of apple, Google, Microsoft, alibaba, benz, BMW, Toyota, Amazon, Qualcomm, European space agency can fund it. But I doubt it will happen as it's considered more strategic investment with military implications. But I am still hopeful like internet(which was designed for military pur…

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

I know nothing about satellites but couldn't the Starlink constellation be used for positioning in some way? It already has twice the amount of satellites and will have an order of magnitude more than any other current positioning system.
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