Ken’s posterous

My brother made an excellent point that an EMP is not the only event that could take out a ship full of GPSs. A solar storm (it would have to be one much larger than anything on record) could take out multiple satellites.

I once studied the "Bastille Day Geo magnetic Storm" when I worked on upper-atmosphere physics and Sun-Earth interactions at the Laboratory for Atmosphere and Space Physics. An anecdote about this storm is that on Bastille day the British and French fly homing pigeons across the English Channel. These birds navigate, as many animals do, using the magnetic field lines of Earth. Very few of the birds arrived at their destination the year of the severe storm.

I therefore presume a large storm could take out both satellites and compasses, leaving us fully dependent on a sextant.