> Why build a timescale that ONLY works for the Moon? Then, we need atomic clocks on all spacecraft ... or a Martian timescale. Scalability is key here, and we are lucky as we can build a GALACTIC timescale through ... you guessed it .... pulsars! A pulsar-based-timescale using the timing of pulsars around the galaxy, so all locations and receivers can tap into it universally. This also has the benefit of not having to build GNSS on the far side of the Moon, protecting its pristine radio heritage for #astronomy. Here's some further reading: https://academic.oup.com/mnras/article/427/4/2780/971096?log...https://academic.oup.com/mnras/article/491/4/5951/5612203https://www.esa.int/kids/en/news/ESA_test_a_new_pulsar_clock
GNSS could just turn itself off on the far side of the moon? You could even use a mechanical timer to turn the whole satellite back on — Battlestar Galactica style low tech solutions.