TLDR: US relies solely on GPS satellites for broadcasting time and navigation data, which are increasingly vulnerable to militarization of space. The US decomm

TLDR: US relies solely on GPS satellites for broadcasting time and navigation data, which are increasingly vulnerable to militarization of space. The US decommissioned its backup ground radio-based LORAN system in 2010 and has no replacement or alternative. China by comparison has Beidou satellite GPS, a national LORAN system, and is building an underground fiber-optic system, for doubly-redundant backups to Beidou.