Every Halloween we present a familiar horror story: You wake up. Emergency and rescue radios are down. Your location app is offline and planes are grounded worldwide. You attempt to go shopping, but the credit card isn't working. The ATM is down, too. As the day progresses both cell and internet service are lost, stores and restaurants are closed, and you can't even get gas. By the next morning the power is out.

The foundational need to know our location and time is at the heart of position, navigation, and timing (PNT) infrastructure. For the last half century, PNT and GPS (the US Global Positioning System) have been interchangeable; there are 8 billion GPS receivers in the world – one for every person on Earth - and GPS pervades all aspects of our lives: our location on digital maps and ridesharing apps, commercial and airline navigation, the timestamp on ATM, credit card and stock