[M T]

Just to put jamming strength into perspective, I'm going to paraphrase what someone else said one time:  Receiving a GPS signal is like watching a light bulb that is 50% further away than the diameter of the earth.

(The Russian GLONASS satellites have transmit power around 100W and orbit at an altitude of 11,900 miles.)

As for the miracle of GPS, here's something to recognize (taken from here):
General Relativity affects the positioning info from GPS by about 14 km/day.
Special Relativity affects the position info by about -2 km/day.

Combined they would affect positioning by about 11.5 km/day, or about 38.4 microseconds per day.

[M T]

Just to put jamming strength into perspective, I'm going to paraphrase what someone else said one time:  Receiving a GPS signal is like watching a light bulb that is 50% further away than the diameter of the earth.

(The Russian GLONASS satellites have transmit power around 100W and orbit at an altitude of 11,900 miles.)

As for the miracle of GPS, here's something to recognize (taken from here):
General Relativity affects the positioning info from GPS by about 14 km/day.
Special Relativity affects the position info by about -2 km/day.

Combined they would affect positioning by about 11.5 km/day, or about 38.4 microseconds per day.