[flipflipper]

>However, the power supply uses a more complicated design to provide electrical isolation between the spacecraft and the clock. I'm not sure, though, why isolation was necessary.

I believe this is to maintain a single point ground, usually the chassis on a spacecraft. The chassis of the clock is probably connected to the isolated side's ground, which avoids ground loops when the clock is integrated into the S/C.

More detail on grounding and isolation in S/C is covered here: https://standards.nasa.gov/standard/nasa/nasa-hdbk-4001

[analog31]

I wonder if there would be a fair amount of current flowing through the "ground" of the craft as it went through the ionosphere and then into whatever ion flux the sun is spitting out. They might have to be really careful about treating the whole chassis as a circuit.