It's actually really interesting what a relatively tiny amount of Pu-238 is needed to power deep space missions for decades, 36lb (16.3kg) of Pu-238 amounts to

It's actually really interesting what a relatively tiny amount of Pu-238 is needed to power deep space missions for decades, 36lb (16.3kg) of Pu-238 amounts to a sphere with a radius of 5.82cm according to wolfram alpha.