I would love to see how they would squeeze the antennae in there for a start. One with a semi decent SNR. How you are supposed to fit a decent atomic clock, transponder, processor and the rest of the gubbins in something smaller than a packet of rice crispies, only the gubnermint can explain.

Surely Britain's security relies on NATO which presumably relies on the US GPS? Is it planned to switch to Galileo or somehow incorporate it as as a substitute? If not, then I presume this is more about losing future work-share and the benefits of the what has already been invested?

Or are other there other 'security' concerns that most aren't generally aware of?

Which we brought upon ourselves of course - people were warned what would happen but they preferred Blue Passports and £ 350 mm a week for the NHS - or maybe a new plane for Boris................

Plus an annual customs bill to business that is alone 4 billion more than the cost of membership.

Is there really a need for more Sat Nav systems?
I can understand that some satellites may reach their life expectancy or orbit decay, but what we have now isn't instantly up to date for every new road, either in the UK, Europe or elsewhere....
as for in car systems, you usually pay through the nose for "updates" which aren't current, simply the latest possibly months old) updates.

Currently, there are several manufacturers each with a range of models, some with better clarity, size of screen or specialised for HGV's motor bikes etc....

Do they get their mapping from different satellites?

As for the Brexit comments, I'll just say that I believe democracy to be the will of the majority. We can all speculate but it ought to be concomitant that a majority decision should then be supported by the minority to make it work in the easiest way possible for the good of the Country, not snipe and obfuscate every step of the way.. 'nuff said.

More or less my point: the urge to forge ahead, and above all not to be painted as somehow undemocratic has prevented any meaningful debate of either what the meaning of the referendum result was, or what our future options are.

I cannot imagine history treating this period of British politics kindly.

However, if this results in a long overdue wake up call to the UK government of the importance of preserving domestic strengths, and capabilities which have been allowed to wither because apparently the market will always be infallible in knowing best, then maybe something good might come of it.

This whole shambles makes losing the American Colonies look like a master stroke IMHO - as for cutting off your nose to spite your face you'd have to go back to Troy I think for as bad an example of lunacy..................

drustsonorerp - agreed - most MPs knew it was a crap result but felt they had to honour their less well informed constituents views. Lack of moral courage.

There is a good appraisal of the issues in the current Aerospace

It depends a LOT on the nature of the "democracy". What you say is true of a pure democracy. The majority rules. But that can be very very bad if the majority decide to do something stupid or something evil. In the US we have a Constitutional Republic, with the people's representatives democratically elected and bound/limited by the Constitution. There's a vast difference.

I agree, as evidenced by the way in which everyone, in particular reactionary Tories and the right-wing media, got behind the democratic will of the people to join the precursor to the European Union in 1975, and how since then they have all worked together in a selfless spirit of national unity for the good of the country. Oh, wait...

Parliament voted for a referendum and agreed to be bound by the result. Parliament voted, overwhelmingly, to send the article 50 letter.
Now, can we please resume the GPS discussion?

What a load of bollocks.

Indeed <insert Mel Gibson meme here> the fallout for NOT following the majority vote will make Brexit look like a piece of cake....

The mapping does NOT come from the satellites. The satellites, and the local receiver, give a position in space--latitude and longitude, and height above some calculated datum. The maps that translate that into a position on the road, or wherever, are held on the device, and the frequency of their updating (and their accuracy) depends on the map supplier. This is why, on the whole, Google maps wins, because you download a map pretty much every time you use it, and they keep their maps up to date.

Another set of satellites won't affect this situation, nor is it being proposed for the convenience of motorists.

ORAC talks of Galileo becoming obsolete.

We hear a lot of the Russians and Chinese developing anti-satellite weaponry. Is this what really makes Galileo obsolete and are all three current GPSs equally vulnerable ?

Can our successor system be designed to defeat or avoid this threat ? – or must off-the-shelf technology and low orbit leave our proposed system as vulnerable as the others ?

We do? Sorry I didn't realise it was 1969 again. Russian ASAT program dates back at least that far. The Americans have one which launches off a F-15 following a zoom climb, the Russian one launches from a site like an ICBM.

This thing about these cubesats replacing Galileo or dedicated satellites is just BS.

(Listen in now sis 'cos I like you, we've got a lot in common.)

To pick up a signal on the ground using a nondirectional antenna mandates a directional antenna on the satellite _or_ a very very porky transmitter. The current GPS signals go out at 25w and a directional antenna is used. The antenna gain gives a directed power equivalence of about 300w. (That means, if you had no directional antenna you'd need to transmit with 300w to achieve the same signal strength at any given receiver.) A cubesat can generate about 20w max. So the generated power budget doesn't even cover the required transmit power, let alone the much greater input power needed into the transmitter and then the power for all the other electronics, computer, clock, stabilisation etc.

There's also a very real question as to whether all the required components would physically fit into a cubesat.

The altitude of a cubesat is also very low which results in an orbital period of only a couple of hours. Assuming a 45 degree orbital inclination and an observer on the equator any cubesat will be visible for approximately 10 minutes per orbit. The current system results in a Doppler shift at the receiver of +/- 10KHz changing over a ~6h satellite visibility window. Cubesat altitudes make that +/- 80KHz over 8 minutes. So compared with 'standard GPS' the signal must be found in a frequency range 8x the size and within 1.25% of the time (= 80x faster). For a modern receiver that's trivial but it's just one example of how changing the satellite configuration can make a problem 8x80 = 640x harder.

In addition, cubesat LEO orbits are unstable - air drag is significant. Altitude losses of up to 10m per orbit have been measured. A 2m satellite altitude loss between entering and leaving a ground receiver's field of view is feasible. The ephemeris would have a usable lifespan of minutes. You would need a ground tracking/control facility in each sector where people would be using the system - because ephemeris data for a satellite that's just come over the horizon would almost certainly be outdated. With the satellites being so low the ground visibility radius would be ~1700km - so your ground station would have to be at least that close to your forces in order to be able to update at least 50% of the satellites they'd have in sight with one good ephemeris value.

The only thing that makes it objectively impossible is the power requirement. If we handwave that away - nuclear cubesats! - okay so then our GPScubes dont need orientation (a prereq for directional antennas) as they'll just belt out 10kw in all directions. The satellite's working parts then have to fit... And not melt... And the receivers have to be full of Xilinx's FPGA wonderfulness and able to apply a 500hz bin FFT to a 160khz range in five microseconds... And it's still all for nothing because the satellites themselves have unstable orbits. And our best case location is the sum of the best case orbital variance for each satellite we're using, factored for receiver aspect.... So each satellite could lose up to 10m alt per period, which of course means a reduced orbital speed... Starting at 450.01km altitude a 10m drop to 450.00 would mean the orbital speed would decrease by 0.559 cm/sec... Final orbital period would be 01h33m35.2s. Assume the ephemeris was updated one period before we gain sight of it, then during that period say it'll lose 10m alt and 0.559cm/sec orbital speed... so our average speed variance during that period will be half that so it'll have not-travelled 5615.2s x 0.2795cm/sec = 15.7m retrograde mean anomaly position error... then 10m altitude position error... So worst case pseudorange error...Satellite rises coming basically straight at you fudge the cosine error to zero for both terms so 15.7m error. You need 4 for a location so worst case = 4 satellites coming straight at you = position uncertainty a circle radius 15.7m = 31.4m. Then add all the errors that affect GPS. Splendid system. Solid gold.

Dunno why you can't figure this stuff out for yourself really it's not rocket science, just a bit of trig and some light reading.

Sorry I asked