SNAP-9-A was a Radioisotopic Thermoelectric Generator (e.g. a space nuclear generator) launched by NASA in 1964. The Department of Defense weather satellite that carried it failed to achieve orbit and it burned up in the atmosphere over the Indian Ocean. SNAP-9-A's power unit contained about 17,000 Ci of Pu-238, and as it fell from the upper atmosphere the particles (ranging between 5 to 58 um in size) entered the earths air, water, soil, and ultimately (though the food chain and otherwise) you and me. Today ("they say...") every human being contains a little piece of plutonium from SNAP-9-A in his or her lymph nodes (presumably not enough to do any damage).
Something to think about, especially with the prospect of U.S. National Missile Defense (e.g. the militarization of outer space) on the horizon. | 
