[tanzam75]

> I wonder how robust the GPS system is. Could an unexpected space phenomenon bring it down? What would happen if a rogue nation started shooting down the satellites?

GPS is not the only system. We currently have about 2.7 global satellite navigation constellations available for use.

The American GPS and the Russian GLONASS are both complete. The Chinese Beidou system is about 40% complete. The European Galileo system is about 30% complete. Each system also has about 20% redundancy in the form of on-orbit spares.

Dual-system GPS/GLONASS receivers are now nearly everywhere. I was just looking at a phone that has a triple-system GPS/GLONASS/Beidou receiver. In a few years, quad-system receivers will be commonplace.

A rogue nation would have to shoot down about 1.9 constellations, or about 60 satellites, before we drop below full coverage.

The American, Chinese, and European systems have the same orbital inclination. If a gap opened, any satellite from any of these three systems could theoretically fill that gap. It would take some time to reposition the satellites, though.

There is also additional redundancy in the eastern hemisphere. India and Japan have satellites that provide regional coverage. Part of the Chinese system also operates as a regional constellation.

At this point, the rogue state is at war with the US, Russia, China, the EU, India, and Japan. They might as well just surrender.

[spdustin]

It would take only one nuclear device being "detonated" in low orbit, to wipe out nearly all of the satellites in a large area of that space. The resulting EMP may wreck quite a few ground-based systems too, IIRC from a book I read recently. Can't recall the name, though...

In any case, disrupting satellite-based navigation is the simplest kind of rocket science: a missile that just has to go up and then detonate, no aiming required.

[tanzam75]

> It would take only one nuclear device being "detonated" in low orbit, to wipe out nearly all of the satellites in a large area of that space. The resulting EMP may wreck quite a few ground-based systems too, IIRC from a book I read recently. Can't recall the name, though...

A nuclear weapon detonated in low earth orbit would not destroy a single global navigation satellite. They are not in low earth orbit.

A nuclear weapon detonated in medium earth orbit would wipe out between 0 and 1 navigation satellite, depending on how close you get. The satellites just aren't that close together.

An EMP would destroy electronics on the ground, but this will be a systemic effect. Satellite navigation would be collateral damage. When the ground-based electronics are replaced, though, the satellites will still be working.

> In any case, disrupting satellite-based navigation is the simplest kind of rocket science: a missile that just has to go up and then detonate, no aiming required.

Nuclear weapons are powerful, but they still have to obey the laws of physics. If you get far enough away, the inverse-squared law makes even a nuclear explosion look like a firecracker.

A 1 megaton nuclear weapon would have to be detonated within half a kilometer to damage a satellite physically: http://www.projectrho.com/public_html/rocket/spacegunconvent...

The shielding needed to protect a satellite against EMP only adds 5% to the cost of the satellite: http://fas.org/spp/starwars/congress/1997_h/h970716u.htm

So basically, it's going to take one nuclear warhead to destroy one navigation satellite. If a rogue nation has 60 nuclear warheads, it's hardly going to waste them to take out 60 navigation satellites.