India completes its GPS alternative, for the second time India has successfully conducted the satellite launch needed to re-construct its Indian Regional Navigation Satellite System (IRNSS). The Indian Space Research Organisation’s Polar Satellite Launch Vehicle PSLV-C41 ascended on Thursday, April 12th. Atop the craft was a satellite designated IRNSS-1L, the last of seven …
That's definately the case of the American ones, where the designers assumed that in case of nuclear war things might not work properly, so the missiles take star fixes while in orbit to ensure that they land "near enough".
Ultimately, maybe a handful of people know if competing missile systems have comparable functionality and the only way the general public would find out is practical demonstration, so let's hope that we remain in the dark. ;/
For some reason I can't help thinking of the Great Trigonometrical Survey when reading about India's GPS, if only because it would have made the whole process much easier.
https://en.wikipedia.org/wiki/Great_Trigonometrical_Survey
Although the book 'The Great Arc' by John Keay is a much better read.
I suspect it is much less about guiding neuks to terminal global warming and much more about mitigating the major economic costs of the loss of precision navigation and timing. Few folk realise how much we take for granted would go TITSUP in the event of prolonged GPS outage (like mobile phone networks and digital TV, etc, and the services that rely upon them) to other things that do have fall-back options but less efficient/safe (like ship navigation and air traffic control).
What requires precision timing in mobile phone networks or digital TV ?
Stable data timing (within 1 part per million) I can understand but what is the requirement for high precision absolute timing ? As the clocks on mobile phones and digital TVs are low precision devices, they already adjust to whatever the timing is on the transmissions from the phone or DTV masts.
If you have a big, national TV network then it has multiple transmitters. There are two ways to do that:
1) allocate 4-6x as many radio channels, and put adjacent transmitters on different channels so they don't interfere with each other. This is simple, but wastes a lot of expensive radio bandwidth.
2) put all the transmitters on the same channel and ensure they broadcast the exact same signal at the exact same time. The "exact same time" part requires incredibly good absolute precision, which is usually done by having a good GPS receiver built in to every transmitter. This is called a "Single Frequency Network" (SFN) because it uses one radio frequency.
They need pretty good reference clocks for SFN. They use GPS to save money at install time. It's an economic bean-counter decision, not an engineering decision.
Timing could also be distributed by fibre or microwave links when the distance/latency is known, but local clocks are the best solution. A GPS receiver is very cheap.
I understand what you said - however that still leaves some questions.
1) With digital TV transmissions - if there is a local station in the multiplex from one transmitter that is not in another then the transmitted signals will be different even if they are on the same frequency.
2) As mobile phone mast are NOT transmitting the same signal (as they are talking to different phones), why do they need the precision timing ?
I am just trying to understand the reasons that require the precision timing.
"As mobile phone mast are NOT transmitting the same signal (as they are talking to different phones), why do they need the precision timing ?"
Presumably to allow triangulation of the mobile's location. Maybe also so that base stations on the same frequency which overlap in coverage area can interleave their transmissions.
Yes, with a SFN you can’t do regional TV as easily. That’s probably one of the reasons we don’t do much SFN in the UK. (The main reason being it would have required lots of old analog TV aerials to be replaced. At analog switch-off in the UK, the main digital channels were moved to the old BBC2 analog TV frequency from each transmitter, which meant the old aerials worked, but ruled out SFN).
But if your regions are big enough, you can do a SFN covering a single region. I believe there’s at least one of those in the UK.
"Stable data timing (within 1 part per million) I can understand but what is the requirement for high precision absolute timing ?"
An *absolute* time capability of 1 part per million would allow a GPS to locate itself *somewhere* within a sphere with a radius of something more than 300 meters, exact size depending on other sources of error.
Since the GPS measures the distance to the satellites by calculating the time the signal took to get to it, it determine the absolute time of arrival of the signal.
Indeed, the power drain and radiation exposure of your phone 'talking' to a satellite would not make most users happy at all.
Devices which do talk to the satellites are much bulkier than phones and come with big batteries. In NZ you can hire them when going bush, you cannot rely on mobile coverage in the back of beyond. Get into trouble and you activate your beacon and it talks to the satellite giving your position and continuing to broadcast it so the rescue helicopter can locate you easily and quickly.
They published a picture of a hunter in broken forest recently, he was VERY hard to spot but because he had activated his beacon the helicopter crew focussed down and spotted him. No chance if they were just relying on a visual scan. Marine ones which are activated by water are also pretty much essential.
But your cellphone, not yet.
Look at USA spending on Military vs Education and Healthcare, both of which are very poor for the average US citizen compared to OECD / GDP per head.
You're not looking at that US discretionary spending pie chart that's going around, are you? The one that shows US military spending as 54% of the federal budget? The USA's defense & security spending is about 18% of its total federal budget, while two of its welfare departments - Health & Human Services, and Social Security - are individually larger than the Department of Defense. I mean, that's a huge amount of military spending, but it's not dwarfing or draining other departments' budgets.
Regarding US educational spending, including state and local budgets, that's larger than the OECD average both as a percentage of its GDP (7.3% vs 6.3% OECD average) and per capita ($15,171 vs $9,313 OECD average). Not that the results are better, but the US spends more on its students than the OECD average.
Overall welfare / social services spending by the US is below the OECD average, but it's 19.3% isn't vastly lower than the 21% average.
Given that the Indian Mars mission was cheaper than the film 'The Martian' I think you might protest too much. And it hasn't cost billions, the hole IRNSS system has cost about 400 million US$.
But in any case it's not as if they loaded the cash onto the rocket and blasted it off. The cost is salaries and buying stuff from, mainly Indian, contractors. So the money supports wage earners, who go to shops and buy stuff, that's made by other people, who thus earn a living, and can afford to buy stuff etc.
Less flippantly, and reducing your argument to it's basics, why are you applying nationality to this issue.?Surely it is equally immoral that you squandered money on a skinny latte/artisan ale/avocado smoothie or whatever yesterday? You could have drunk tap water and spent the saving on alleviating poverty and deprivation in your own community?
However their requirement was for local coverage - not whole world so they could use fewer satellites in geostationary or inclined geostationary orbits rather than a large number in low earth orbit. There is also a military advantage to using GSO rather than LEO in that there is far less chance of a satellite in GSO being taken out by an opponent in the event of a war. The IRNSS also has a feature that could be useful for civilian use - text messages can be sent to a region to warn of problems like a cyclone.
"From what I remember, IRNSS is not compatible with the other GPS systems"
The only systems that are compatible are Galileo and GPS block-III, which hasn't actually launched yet. If you want to use multiple different satnav systems, you need a different receiver for each one. India is no different from all the others in this regard.
"Without arguing about the techy element of how compatibility, is actually delivered in hardware, many modern devices , from phones to smart watches, include GLONASS compatibility and the latest Huawei smartphones, unsurprisingly, integrate Beidou compatibility."
The "techy element" is the only relevant thing about compatibility. Many modern devices can use multiple different satnav systems because they include multiple different receivers, along with different software to interpret the signal. Doing this costs more money, takes up more space, uses more battery, and so on, which is why most devices don't do this, and even those that do generally only cover a couple of the more regionally relevant systems. From a consumer point of view it doesn't make much difference, but when it comes to criticising India for "not being compatible", as the OP did, noting that it's possible to include lots of different hardware to cover different systems is utterly irrelevant.
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