Galileo: Europe's version of GPS reaches key phase

[dipsydoodle]

The third and fourth spacecraft in Europe's satellite navigation system have gone into orbit.

The pair were launched on a Russian Soyuz rocket from French Guiana.

It is an important milestone for the multi-billion-euro project to create a European version of the US Global Positioning System (GPS).

With four satellites now in orbit - the first and second spacecraft were launched in 2011 - it becomes possible to test Galileo end-to-end.

http://www.bbc.co.uk/news/science-environment-19933989

[Judi Lynn]

1. Interesting! Thanks. Rec. n/t

[Silent3]

2. I think a great job-creating infrastructure project would be...

...a completely ground-based GPS back-up system. We've grown very dependent on GPS, but it's very likely that someday a major solar storm will severely damage the satellite-based GPS system.

In a related matter, we should be beefing up the ability of our power grid to withstand a major solar storm as well.

[DetlefK]

3. Establishing multiple lines-of-sight would be a problem.

GPS measures your position by triangulation. That's easy with satellites, because you always have the half-sphere of sky above you which means, you can be seen from multiple positions in space.

On earth, the horizon is the problem: A "satellite" further than 50km away (depends on its height) will slip behind the horizon, because of the curvature of earth, causing problems with precision and signal strength.

[Silent3]

4. I'm well aware of the many problems

But a back-up system doesn't need to be as thorough or as accurate as satellite-based GPS, just better than nothing at all.

We can already do rough geolocation via cell phone signals, measuring timing and phase differences between multiple cell phone towers. Improved geolocation based on, or overlapping with, that same technology is the sort of thing I have in mind, at least for land-based applications.

While flying over land, aircraft might be able to use the land-based back-up system. Aircraft flying over water, and ships at sea, would need something different. Balloon- and buoy-based transmitters? Not sure. It's probably something that would require a fair amount of expense to deploy and maintain -- but hey, I was aiming not just for the end-result of a good GPS back-up, but a job-creating infrastructure project too.

[DetlefK]

5. Number-crunching

Earth has a radius of 6371km.
Let's say, the transmitter is atop a 100m-high building (that's 25 to 30 floors).
That means, the transmitter could reach objects up to a distance of
sqrt(6371.1² - 6371²) = 35.7km (line of sight; distance on ground would be slightly larger)
before they slip behind the curvature of earth.

Earth has a surface of 5.1*10^8 km², which means you would have to install approx 400,211 transmitters of this type.
Everywhere.
From the midst of the pacific ocean to the Sahara to the Antarctic.

If you make the towers twice as tall (Eiffel-tower is 195m), you get a range of a whooping 50.5km, and you will only need 200,122 transmitters.

[Silent3]

6. I've heard about the possibility of using balloon- and blimp-based transceivers for cellular signals

...which, while they come with their own messy problems, can cover much larger areas than completely ground-based systems.

While a balloon won't hold a very stable position, it would be high enough to easily "see" multiple widely-spaced ground-based transmitters. The balloon could compute its own position, then end users "seeing" that balloon, and other balloons, could in turn use those computed positions to compute their own positions.

There's no way in the course of a few message board replies I can work out all the kinks and complications, but I don't get the feeling that this is an insoluble engineering problem. It's complicated, probably more expensive than arrays of satellites (which are already expensive enough), but I think we've reached a point where a huge amount of global commerce and productivity, not to mention human safety, has become reliant on GPS, enough so that even an expensive insurance policy may well be worth the cost.

[DetlefK]

7. Helium is getting more and more expensive. Blimps would be hot-air or hydrogen.

[Silent3]

8. Such a Debbie Downer! :) n/t