Wired: China's Beidou satnav system, 35th bird in orbit. Tired: America's GPS. Expired: Britain's dreams of its own

The delayed launch of China's 35th and final third-gen Beidou satellite today gives the Middle Kingdom a completed advanced global positioning network. The so-called BDS is now the fourth global satnav system up in space; the others being the United States' GPS, the somewhat incomplete Russian GLONASS network, and Europe’s …

[GreenJimll]

And next: commercial positioning

I wouldn't be at all surprised to hear that Elon's Starlink that SpaceX are launching at a rapid rate of knots contains some kind of positioning subsystem. The Chinese have put their 35th Beidou satellite in orbit after 20 years of effort. SpaceX launch 50-60 Starlink birds on each Falcon 9 launch. Even if current Starlink birds don't to positioning, that rate of deployment and tech iteration means they possibly soon could.

[MatthewSt]

Re: And next: commercial positioning

My (very rough) understanding is that they probably will, as all they need is a very accurate clock (to 40ns) and to know where they are. That and the ability to broadcast both of those things. The rest is just maths calculated by the receiver

[Malcolm Weir]

Re: And next: commercial positioning

I'm not sure that Starlink _is_ compatible with a GNSS application. I think there are three main issues:

-- As I understand it, the individual Starlink spacecraft have some degree of autonomy in order to avoid each other. So a given article may not actually know, precisely, where it is! Maybe it will be good enough, but...

-- I also doubt they have a highly accurate clock, because that adds cost, and as the whole point of the constellation is to maintain low-latency connections, whatever timing information a given spacecraft might need would be amply addressed by an IEEE1588 clock synchronization system.

-- The terrestrial RF links are narrow, with the system working like a cell system handing off "calls" to different access points/satellites and beam-forming used to solve the power problem. This means that the footprint of a beam may be tiny, e.g. a 10km circle.

So a classic GNSS is probably not on the cards. But if a Stalink satellite "knows" enough about a ground-station's location to steer a beam to it, that would presumably make it theoretically possible to get the position of that 10km circle. And successive spacecraft could, over time, improve on that ... but this is all assuming that the system doesn't already depend on GPS to steer the beams to the ground stations (which may or may not be the case, but I wouldn't rule it out!).

What I do think is very plausible is that, if there's a good business case, that there may be a GNSS variant of the Starlink spacecraft. One very specific business case that I know SpaceX has put thought into is... how do you locate yourself on Mars? If the answer to that is a Martian GNSS, an Earth variant is an incremental and useful addition, and Starlink proves they have the technology to launch and manage such a constellation...

[Anonymous Coward]

Re: And next: commercial positioning

They must have a low-drift clock on board: The relative speeds in orbit are so huge that one is practically mandated to be able to predict with any confidence where in space it would be relative to another body a revolution or two ahead in order to not collide with it. Of course it could be trained to another system like NAVSTAR but if that were to stop working in the future for any reason, it could be catastrophic.

PTP as you mentioned only works in a static environment. Even then it's not considered good enough for some terrestrial enterprises, let alone something more mission critical.

If the satellite locally knows its ephemerisis and the time, it can function as a positioning beacon. And if it should decide to deviate from its course, it will simply stop broadcasting for a while and let the others in the constellation provide the fix. (It's all maths at the receiving end.)

[TDog]

Re Low Drift Clock

Purely as a thought experiment, I wonder if a ground based clock could be used. Broadcasting a synchronised signal regularly these could be picked up and echoed back to the transmitter. The lag would give an indication of the straight line distance plus an internal delay time (signal processing etc.)

On it's own this would probably not provide sufficient information for the ground based system to provide clock rectification but if each recipient also broadcast to it's neighbours (as must happen already to allow chaining of the signal beyond the visual horizon) then they too could rebroadcast that signal with an individual identifier.

Analysing these signals would allow the creation of an exact image of the net with different time delays due to the differing distances. It would now be possible to transmit individual time sequences such that each receiver would receive the time signal simultaneously (OK - general relativity sort of negates that but it is also calculable if necessary) so that the clocks on the satellites could be reset every whatever time interval to ensure they were all withing 40 ns of a specified target time.

Slightly complex but should be doable and retaining the time source on the ground would make the individual satellites a lot cheaper - multiple ground stations would also obviate a single point of failure.

[Anonymous Coward]

Re: Re Low Drift Clock

It seems rather obvious that if a ground based transmitter were used, it'd be quite easy to jam it, even if it's sufficiently encrypted to avoid spoofing.

Enough smart people all over the world have spent enough time thinking about the problem during the last decades, it's unlikely a big EUREKA discovery will happen on a comment thread, even one as sophisticated as ElReg's.

[Anonymous Coward]

Re: And next: commercial positioning

Upvoted for ephimerisis.

Made me look it up.

Shoehorning into conversation tomorrow

[Brangdon]

Re: and the ability to broadcast both of those things

That's the bit which would need extra hardware, a lot more power, and a licence from FCC (or whoever). If they had, or were applying for, a licence to broadcast GPS signals, we'd surely know about it.

If it happens at all, it'll surely be after Starship comes into operation. They may take advantage of its larger lift capacity to make the satellites bigger and have more capabilities. Or they may just make a separate satellite type. GPS doesn't care about round-trip latency, so doesn't need to be a low orbit.

[S4qFBxkFFg]

Re: And next: commercial positioning

While noting the other replies, a problem would be that I think the ground receivers are too large for use in phones, and apparently depend on things like phased arrays. Fine for buildings, ships, and large aircraft; probably doable for smaller vehicles down to car size; but impractical for anything held or even carried.

[Brangdon]

Re:ground receivers are too large

The current Starlink receivers are for receiving and sending internet. A positioning system aerial would have a different purpose and size. It wouldn't need to transmit at all, so it wouldn't need to aim a beam. There's no reason for it to be bigger than a normal GPS aerial.

[c1ue]

Re: And next: commercial positioning

In theory, any satellite can be used for positioning.

In reality, unlikely. Among the issues:

1) Positioning systems all require at least 1 ground station connect. There is more than enough variable atmospheric interference that it has to be accounted for.

2) Power requirements are fairly significant. While the signal at Earth surface isn't strong, the satellite is broadcasting over a very wide area (line of sight Earth coverage). The GPS block 3 satellites are 2 tons in oribit and have 1.9 kilowatt in solar capacity with comparable storage.

3) Ledger info - you can't just throw up a positioning satellite, the users have to have a lexicon to find and handshake to its very weak radio signal.

A microsatellite system that is constantly repositioning, relaunching etc just doesn't seem like a good fit for the above, even if the power requirements are reduced because of closer proximity to the ground - because that closer proximity also makes the ground station atmospheric compensation extremely difficult.

[NeilPost]

Re: And next: commercial positioning

But when HMG get stuck with bankrupt OneWeb’s infrastructure they will retask NHSx and leaky data Empress Dido to develop a ‘World Class’ location tracing app.

Job done. They can Life for Rent it too.

Heath Robinson will be so proud.

[Anonymous Coward]

Re: And next: commercial positioning

'We've bought the wrong satellites': UK tech gamble baffles experts

https://www.theguardian.com/science/2020/jun/26/satellite-experts-oneweb-investment-uk-galileo-brexit

[John Brown (no body)]

Re: And next: commercial positioning

"A microsatellite system that is constantly repositioning, relaunching etc just doesn't seem like a good fit for the above, even if the power requirements are reduced because of closer proximity to the ground - because that closer proximity also makes the ground station atmospheric compensation extremely difficult."

Do you think it might be possible if you can see many dozens of sats at the same time rather just the 3-10(ish) with current systems? Would the required levels of accuracy per satellite drop in proportion to the number of data points the receiver is able to work with?

[Anonymous Coward]

OT competing organizations, bureaucracy, and lack of accountability

no matter how much I like the EU and lament brexit, that EU bureaucracy, and lack of accountability seem to be an underlying problem for them. Arguably, you can say that it's an underlying issue with any government, national or local, or any large organization. I wonder how the Chinese are doing, with their bureaucracy, and lack of accountability? Perhaps the selective accountability, i.e. "you can be arrested and turned into a 100% organ donor" keeps inefficiency in check? :(

[EnviableOne]

Re: OT competing organizations, bureaucracy, and lack of accountability

Acountability is an issue, but ESA is full of them, its leadership is fighting with itself, and its not a particularly well functioning organisation.

The Chinese and Russian Systems have probably suffered with less issues due to the Single nation state involved and the more authoritarian structures from the top down, along with the National Spotlight and Political will to get the systems operational

[Dr Scrum Master]

Convenient

"BDS, we note, has more birds in orbit than Uncle Sam's GPS, and has extra coverage over south-east Asia."

How convenient for the PLA Navy in the South China Sea

[Yet Another Anonymous coward]

Re: Convenient

So China has military coverage for the water around its coast and the USA has coverage world wide - proves Chinese hegemony

[Anonymous Coward]

Re: Convenient

The official release actually says Asia-Pacific, it's a bit odd ElReg wrote South-East Asia, unlike other news outlets.

http://en.beidou.gov.cn/SYSTEMS/System/201806/t20180614_15002.html

http://en.beidou.gov.cn/WHATSNEWS/201812/t20181227_16837.html

[PaulVD]

There is no such country as Taiwan ...

... and yet Taiwan is one of the first customers for a Chinese satellite positioning system. Gotta love the hypocrisy of today's Middle Kingdom.

[Malcolm Weir]

Re: There is no such country as Taiwan ...

That shows the basic misunderstanding of PRC/ROC relations. The PRC position is that ROC (Taiwan) is a bit like Hong Kong and Macau (or at least how Hong King was a few of years ago): It's got an autonomous government that sometimes/often does things Beijing doesn't much like... but that's an internal matter, and other countries had better not interfere with Beijing/Taipei disagreements (or Beijing/Hong Kong ones).

Taiwan thinks itself independent. But that's "just" another of those Beijing/Taipei disagreements.

So from Beijing's standpoint, of course Taiwan should be a customer of Beidou... they're just another part of China. Slightly odder is that Taipei decided to send their cash to Beijing, but its obviously the better value for money given the coverage.

[W.S.Gosset]

Drones (related)

Not many people realise but drones all auto-selfstabilise.

Originally with gyroscopes but they're heavy, bulky, and expensive.

All modern non-specialist drones use GPS. Sub-second sampling, comparison of position, comparison with received control signal, auto adjustment.

Hardware and cost: a startlingly tiny GPS chip (smaller than a microSD) and less than A$1.

It occurs to me:

Given that DJI make the vast bulk of retail drones, is it possible that standard retail drones could become increasingly difficult to control, unless you buy the premium edition, which uses the Chinese GPS, with the existing standard software once more returned to full accuracy. Just a thought. I've seen far more cynical under-the-hood stuff done just in Western commercial software with no larger incentive than P&L.

[W.S.Gosset]

Re: Drones (related)

Whoops. Sorry. To be clear: DJI is a Chinese company.

[Malcolm Weir]

Re: Drones (related)

Not sure what the point would be? Many/most GNSS commodity receiver silicon works with all 4 systems, and so why would DJI degrade their product by using worse signals? What's in it for them?

[W.S.Gosset]

Re: Drones (related)

See immediately above