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Message: <blockquote data-quote="chornedsnorkack" data-source="post: 44629" data-attributes="member: 2148"><blockquote data-quote="Just call me Ray"><blockquote data-quote="chornedsnorkack"><blockquote data-quote="KJ_Lesnick">Plus if that thing crashes...</blockquote>Kosmos satellites routinely do, by design.</blockquote>If anything, this only highlights the concern, though RTGs (Radioisotope Thermoelectric Generators) are fairly common for interplanetary probes and possibly some satellites. Rather than a full-blown nuclear reactor, these devices merely convert the natural radioactive emissions of radioisotopes such as Pu-238 or Sr-90 into electrical power. Though these devices do not generate significant electrical output, they have the advantage of having a long "battery life," especially if a radioisotope with a very long half-life is used (hence why Pu-238 and Sr-90 are the most popular RTG fuel sources).</blockquote>RTG is useless unless the radioisotope has a short half-life. And Pu-238 is nasty stuff. Half-life under 90 years makes it a powerful alpha-ray source - far more dangerous than Pu-239 (half-life 24 000 years) let alone highly enriched U-235 (over 700 millions of years). You cannot scram a RTG! It keeps radiating at the same intensity when the heat is no longer needed, when the isotopes have been scattered to four winds and incorporated in human tissues. Whereas a neutron chain reaction nuclear reactor stops chain reacting when the critical conditions are disrupted and when the contents are scattered, their total activity is very low because of the huge lifetime of U-235...<blockquote data-quote="Just call me Ray">Besides, even a modern "compact" nuclear reactor is going to be huge. The only payload the NB-36 was able to carry was the reactor itself.</blockquote>A RORSAT reactor without shielding weights 130 kg. Not too much to carry on a small general aviation piston plane (when not running, of course!)<blockquote data-quote="Just call me Ray">Never mind the 6 tons of lead shielding it carried just behind the crew compartment, protecting only the crew (the amount of shielding needed for a passenger plane would make said plane more suitable as a submarine)</blockquote>Note that the MTOW of a NB-36 was just 162 t. Airbus 380 or An-225 could carry much bigger payloads.</blockquote>

Verification: What year was Concorde's first flight? (answer has 4 numbers)