Looking at that diagram - is that a Beryllium Sphere?
Tech Sgt. Chen would be proud...
A Beryllium containment vessel with domed ends.
MULTI-HUNDRED WATT RADIOISOTOPE THERMOELECTRIC GENERATOR PROGRAM Part I, Annual Report, 1 January 1973 - 31 December 1973
The toughest challenges were to make sure the RTGs didn't break apart if the rocket blew up on the pad, if the rocket failed to make orbit, and if it went into the wrong orbit and crashed back into earth sometime in the future. The RTGs are powered by highly toxic plutonium. There were lots of civil protests against launching the RTGs because of the risk of plutonium poisoning of a lot of people.