Notable is that it's not the actual half-life of the Pu238 that causes the majority of the performance regression, but the degradation of the materials that con

Notable is that it's not the actual half-life of the Pu238 that causes the majority of the performance regression, but the degradation of the materials that convert the temperature differential into electricity. In other words, they could have lasted a lot longer. But of course they've outlasted their design life many times over.