Post Galileo
Ecce Homo! Loquitur...
Thread Starter
ion-Berkeley
Block III GPS May be the bees knees, though the program seems well behind schedule and over budget, but it’s not something the UK could ever afford. If there is an alternative it would seem to be LEO based.
https://pdfs.semanticscholar.org/487...20a948ec23.pdf
Navigation from LEO: Current capability and future promise : GPS World
Satelles shows improved PNT accuracy from LEO constellation : GPS World
VinRouge, who needs them all? The idea is to leverage the existence of the LEO constellation, not build mini GPS satellites each providing a service.
Block III GPS May be the bees knees, though the program seems well behind schedule and over budget, but it’s not something the UK could ever afford. If there is an alternative it would seem to be LEO based.
https://pdfs.semanticscholar.org/487...20a948ec23.pdf
Navigation from LEO: Current capability and future promise : GPS World
Satelles shows improved PNT accuracy from LEO constellation : GPS World
VinRouge, who needs them all? The idea is to leverage the existence of the LEO constellation, not build mini GPS satellites each providing a service.
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?
Or are other there other 'security' concerns that most aren't generally aware of?
Ecce Homo! Loquitur...
Thread Starter
The Times:
”......Britain is ready to go it alone or team up with another power to set up a competing military satellite system if the European Union excludes it from Galileo, Philip Hammond said this morning.
The chancellor, who is due to meet other finance ministers in Brussels, said that Britain needed full military access to a satellite positioning system in the national interest.
“We need access to a satellite system of this kind. A plan has always been to work as a core member of the Galileo project, contributing financially and technically to the project,” he said. “If that proves impossible then Britain will have to go it alone, possibly with other partners outside Europe and the US, to build a third competing system. But for national security strategic reasons we need access to a system and will ensure that we get it.”......
”......Britain is ready to go it alone or team up with another power to set up a competing military satellite system if the European Union excludes it from Galileo, Philip Hammond said this morning.
The chancellor, who is due to meet other finance ministers in Brussels, said that Britain needed full military access to a satellite positioning system in the national interest.
“We need access to a satellite system of this kind. A plan has always been to work as a core member of the Galileo project, contributing financially and technically to the project,” he said. “If that proves impossible then Britain will have to go it alone, possibly with other partners outside Europe and the US, to build a third competing system. But for national security strategic reasons we need access to a system and will ensure that we get it.”......
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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.
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.
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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.
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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.
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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.
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.
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?
Now, can we please resume the GPS discussion?
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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?
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?
Another set of satellites won't affect this situation, nor is it being proposed for the convenience of motorists.
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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 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 ?
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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.
Ecce Homo! Loquitur...
Thread Starter
LascIlle, I refer you to the first link in my post #22.
It isn’t necessary to duplicate GPS/GLONASS/Galileo; simply leverage their existence to support a more robust LEO constellation to provide the equivalent of their precision service.
It isn’t necessary to duplicate GPS/GLONASS/Galileo; simply leverage their existence to support a more robust LEO constellation to provide the equivalent of their precision service.