GPS has more than 4.5 billion users, including most U.S. military systems and several U.S. critical infrastructure sectors. It is a central element of PNT, but alternative and complementary sources of PNT provide a greater availability of signals, help ensure the integrity of GPS signals, and assure a PNT solution when access to GPS is limited or denied, such as signals over challenging terrain or in contested environments.
![Picture of a deep space landscape](/sites/default/files/styles/cta_brick_small_479x308/public/2019-10/FFRDC-Heroimageweb.jpg?itok=CeZpHuDy)