For example, some of the US Navy's Transit satellites in the early 1960s were powered by non-containerized SNAP RTG's (plutonium) destroyed when they de-orbited, releasing Pu-238 into the atmosphere.

The Cassini Mission was launched in 1997 with 72+ pounds of Pu aboard. NASA calculated the risks of 'inadvertent reentry' beforehand.

[https://web.archive.org/web/20030505132905/http://www.icsu-s...] [https://www.space4peace.org/articles/morenukesinspace.htm]