Multiple low power jammer attacks can cause GPS to lose signal
The government is looking into what technology could be used to protect our gps signals from bad guys buying illegal jammers or spoofers to allow bad guys to take over civilian GPS signals

The GPS signal is very weak, a 30-watt light bulb is 12,000 miles in space, and the smartphone's GPS won't lose lock on such a low-power signal. Interference can come from walking through dense forests, through canyons, inside buildings, driving between skyscrapers, or from GPS jammers. The final effect of GPS jammers is not much different from other causes of interference, they all make you It is more difficult for GPS receivers to identify weak GPS from air signals unless jammers do this by adding noise to the environment
While the actual impact of an outage depends on the cause, an attack using multiple low-power jammers could result in the loss of the ability to monitor and control the system.
Unfortunately, low received power, unencrypted civilian GPS signals have proven vulnerable to jamming and spoofing attacks. Jammers transmit high-power jamming signals at GPS frequencies to prevent GPS signals from being accessed by nearby GPS receivers. Spoofers broadcast fake GPS signals that overwhelm the real signal, thereby manipulating the location, time, or both reported by victim receivers.