For complete details on how the Apollo ground stations stayed synchronized, see "Apollo Precision Frequency Source and Time Standard" [1]. Stations stayed synch

For complete details on how the Apollo ground stations stayed synchronized, see "Apollo Precision Frequency Source and Time Standard" [1]. Stations stayed synchronized to one part in 10^10. Each had two rubidium frequency standards and two crystal frequency standards. Each frequency standard had its own power supply and battery pack for redundancy. The sites were synchronized to the WWV time radio station and VLF signals. The specification for Apollo was to maintain the frequency within 5x10^-11 for a one year period. The VLF system had 1 microsecond resolution. Jitter in the WWV pulse was +/- 0.5 milliseconds. They calculated and measured the propagation time from the transmitting station so they could account for that, within about 1 millisecond. It's amazing how much redundancy and complexity there was for everything in Apollo. Even something like ground station time synchronization that nobody thinks about (except for supernova87a), had teams of people, a bunch of research, and racks of equipment. [1] PDF page 135 in https://ntrs.nasa.gov/api/citations/19650025875/downloads/19650025875.pdf https://ntrs.nasa.gov/api/citations/19650025875/downloads/19...