Spaceship Design: What makes sense, and what's nonsense?

[thrash]

Originally Posted by Anthony

For example, Cassini is mostly symmetrical but has a single long rod off to one side (not sure what it's for... possibly the RTG).

Magnetometer arm, which was sensitive enough that it had to be away from the other electronic components. The RTGs were used to balance the arm, however, since it was light but long and they were dense but close in.