Personally, I'd tend to give most credit for something like this to the era that created it. I mean building something that can be reasonably expected to operat

Personally, I'd tend to give most credit for something like this to the era that created it. I mean building something that can be reasonably expected to operate and maintained in some of the most hostile conditions known to man, for half a century? It's just borderline magical. And NASA of that era did everything just perfectly, nailing all the gravity assists (obviously using computational/telemetry tech of the time), and more. And that applies to everything from that era. We hadn't even put a man in orbit in 1962. 7 years later, we would be walking on the Moon!!! The degree of competence and capability of that era of NASA is something that I think is probably unmatched in the entire history of our species.