It’s interesting and odd to me that Beidou requires two-way communication, as opposed to other satellite tracking systems where the receivers are purely passive and satellites only transmit, not receive. Is there an explanation for why this was done?
I suspect this is either a misunderstanding or just copy-pasted from descriptions of a different earlier system.
It doesn't make any sense to have the ground station transmit to figure out its location. To give a baseline, that's how the original analogue COSPAS SARSAT worked last century, using doppler measurements to get a location over time - and its accuracy was appalling, a human operator has to use equipment to narrow down where the signal is, it takes significant time to get a 1 nautical mile search area. Which is much better than "I dunno, in the sea?" for a lost ship or plane, but you're still going to need a serious search-and-rescue operation to find anybody.
A modern digital COSPAS SARSAT system you may have seen if you're a serious hiker or outback flyer just does GPS, it uses GPS to figure out where it is, then sends a digital signal that says "I need help, here are my GPS co-ordinates" hence the slogan "Taking the search out of search and rescue".
I am highly skeptical of this claim, it's either for higher accuracy of military stuff, or an internet connexion to get a key or the ephemerides or something. But nobody is sending signal to a satellite 21000km from the surface straight from a watch-sized device.
I agree with the thrust of your post, but Um Actually...
The current Breitling Emergency (a bulky men's watch, but it wouldn't look out of place on some big out-of-doors type guy's wrist) is a working PLB transmitter.
So that means signals from it can be received not just 21000km up, but 36000km up where Geostationary birds live.
If you activate it, that watch will transmit the digital signal with its unique ID in it, and assuming you filled all the paperwork out soon after somebody from the relevant local emergency response (maybe a coastguard, mountain rescue, that sort of thing) will be phoning your emergency contacts
"Hi, do you know nraynaud? They went flying today? OK, do you know where they were headed? We have an emergency transmission from their beacon so we're going to send somebody to take a look and check they're OK. We'll let you know, thanks".
A "real" beacon would be better, more robust, better battery life, easier and more obvious for random strangers to operate if you're unconscious, not to mention much cheaper. But the Emergency has the advantage that you'll actually have it when shit goes wrong, because it's your watch.
Unavoidable collection of user location data is the obvious reason. I would absolutely stay away from any device that has support for this positioning technology.
That what was said to the populace. In reality, first gen beidou sats already had functionality to provide atomic clock signal and advanced station keeping. The accuracy was quite lower than from leo GPS sats, but still.
The explanation that beidou 1 was a glorified, super expensive satellite pager, with navigation functionality as an afterthought does not hold water. This "explanation" came much later than the commencement of beidou 1 project.
Looks like some misunderstanding here. No one ever claimed Beidou I was developed as a satellite pager.
The reason Beidou I needs two way transmission is they wanted add pager functionality to its navigation functionality. The party wants more control has nothing to do with Beidou I's two way transmission mechanism. When Beidou I was developed, it's mostly used by military. The party doesn't need "more control" there.
Military use??? You understand what two way transmission means during a conflict? An enemy tunes an antiradiation missile on your frequency, and voila...
China already had military digital satellite coms working by late nineties. For them, it was of even lesser utility.
Perhaps some background info can help. Beidou I was developed in early 2000s. And at that time Chinese military satellite wasn’t advanced at all. Even though beidou I is vulnerable to anti radiation missles, it’s the best they have and at least it worked well for purposes such as border patrol and terrain survey.
My point is that many things in China may be explained by the party wanting more control, but two way transmission of beidou I is not one of them.
The article talks about how it can be used to send messages but my first thought is that it could allow tracking of receivers. A scary thought if it does achieve widespread adoption.
There are two different and independent beidou systems. One is passive and cannot track receivers, and the other is similar to a simple satellite internet.
