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:
In security sense, it seems that the situation virtually rules out the possibility of selectively denying some party GNSS access. So if you want to make your adversary location-blind, you'll have to accept losing location data yourself, right?
Anyone can block the signal given how weak it is, and there are news reports of people doing so (and being charged for it). You can supposedly buy jammers online for not a lot of money.
> ... (I think it was done on the Gulf War) or disable the unencrypted GPS signal (only the US military can decode them).
What you are probably referring to is "Selective Availability" and is the purposeful degrading of the signal to make it less accuracy. The DoD said it will not do so, and has given assurances to the FAA (because planes are now highly dependent on it). The newest GPS III satellites no longer have the S/A hardware:
By 2000 people had figured out to get quite accurate results even with the S/A enabled, so the whole thing not as useful:
If there's a war on it's probably cheaper to just jam in the area of operations.
The GPS system does not have any area denial capability. If the US wants to block it in a certain area they have to deploy terrestrial jammers just like anyone else.
Allies get decryption keys for the military high-accuracy signal.
Military depends on an encrypted signal. If you have the encryption key, you can decode it even with a very high level of interference.
Disadvantage is the key is shared for all users, and if it leaks to the adversary, then they can jam the signal.
straight out of the "having two kidneys is a waste of energy" school of thought
so you must have your own if you don't want US to have a Damocles sword over you
> 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.
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.
Beidou-1 used a two-way link, because it used two satellites in the same orbit. This means the satellite can track all users.
But Beidou-2 supports a one-way link - the same operating principle as GPS, GLONASS and Galileo - where the satellites can't track users. The downside to this design is it needs a lot more satellites, and they have to be in different orbits.
Beidou-2 retains some backwards-compatibility with the two-way link, but if your cell phone's GPS chip supports Beidou, it'll be the one-way link. You'd notice the 20cm antenna and poor battery life if you had the two-way link!
However, this does not seem to be how the deployed version of Beidou works, and this does not seem required with Galileo either.
I also note that Qualcomm produces Beidou receiver chips so these are under American control.
Overall I have the feeling that the article is trying hard to whip up fears over Beidou...
Sure these systems have military applications, but why not talk about those dangers directly instead of trying to portray civilian use as problematic?
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.
> The Chinese feel that they were badly used and partly humiliated by Europe. They were brought into the Galileo consortium as partners, and they paid the EU for the privilege, only to see themselves shut out of Galileo’s controlling bodies...China would have had less influence over Galileo than Japan and India have over GPS, and those two nations have not paid the US a single dime for their cooperation in the signal augmentation systems they are now building .
Take a look at the orbits here : https://www.researchgate.net/figure/Ground-tracks-of-the-Bei...
Though this result is also because BeiDou has intentionally uneven coverage via satellites with inclined orbits that result in much better coverage (and better signal angles, high off the horizon) in asia.
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.
> It seems ridiculous that the US would rely on the fact they can control GPS satellites as form of missile defense
The US most certainly would not entirely rely on that. It would only be one tool in the toolbox. Nuclear ICBM attacks are so dangerous, that the defense by necessity uses a multi-pronged approach. It starts from diplomatic pressure, and technology export controls (see for example the Wassenaar arrangement  that lists the controls for inertial and celestial navigation in chapter 7. The limits on the GPS receivers exist as well, unfortunately I can't point you to the exact source). The actual physical defense options against a moving missile are listed in , such as the Ground Based Interceptors, the Aegis system and the THAAD system. It's all but certain that in case of credible intelligence of an imminent hostile ICBM launch, the US has pre-launch options as well (the current NK ICBM used liquid fuel, and the launch facilities are known and monitored; you will notice that one or two days before any NK missile test the press already writes articles about the likely launch).
Considering all this, would the US neglect the possibility of altering the GPS signal in case it detects a hostile ICBM launch? For example, the reentry vehicle travels at many km/s. Early detonation by only half a second can reduce the impact of the bomb by a factor of 10 easily. If the missile has not GPS signal and only relies on less-than-state-of-the-art inertial and celestial navigation (which may be ok for horizontal coordinates, but not that great of altitude) that may make a huge difference. So my bet is not only that the US will promptly alter its GPS signal, but will have means to spoof the signal from the Russian and Chinese systems as well, and agreements in place with the European Galileo system too. However, as I said before, the problem is more complicated: the Russian and Chinese are not dumb, they most likely have their counter-counter-measures too.
That correction requires data, which needs to come from a third party because the satellites don't transmit it.
In which areas?
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 purpose but now controlled by civilian authorities), locations can be free off selfish national interests.
Pretty significant indicator that the intention is for military applications
Seems like that's the next goal of the big nations.
How can they have more control over the space
While impressive, "how many satellites you can see over a major city" is not an accurate way to judge a GPS satellite network.
To understand why, you have to understand how GPS works. Basically, each GPS has a super accurate clock on board. These are all synced up. These satellites transmit a signal regularly on predetermined schedules.
Your phone or car or whatever else is using GPS listens for these signals. Your device knows when exactly all the satellites sent their signal. It listens and counts how long it takes to receive each signal. With the length of time it takes to receive each signal from each satellite, it can pinpoint your location.
For basic operations you require three satellites for an approximate location.
For precise operations you need line of sight to four satellites, as the fourth enables you to calculate your altitude.
At no point do you need more than 4 in sight.
Why this is important is because the U.S. satellite constellation has 32 currently operating GPS satellites. In addition to those, we have 8 that are currently in space, ready to turn on, but they aren't because there's no reason to have them on.
There's no doubt in my mind these satellites have additional secret reasons for being up there. That's the only reason they'd need that many.
TL;DR:While they do have more active satellites, it's pointless for navigation purposes. Additionally, counting the backup satellites the U.S. Has operational but currently turned off in "standby" mode, we still have more.
EDIT: Not everything I stated is completely accurate. See comments below for some clarifications. Make sure to upvote them if you found them helpful.
Unless you are measuring something with high precision over long periods of time. Like dam flexing or ground shifts.
The more sats you have, the better you'll be at eliminating the signal noise (due to the ionosphere transition and what not).
Also, regarding this -
> "how many satellites you can see over a major city" is not an accurate way to judge a GPS satellite network.
You are completely missing their point - you are in the _city_, a place with tall buildings that give you just a slice of the sky. So the more satellites you have above, the better you chances you will see _enough_ from where you are standing.