RE: satellites carrying atomic reactors

From: Joe (
Date: Fri Aug 24 2001 - 08:12:32 PDT

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    >>After this observation we continued to discuss about
    >>different satellite topics and somehow it came up that
    >>there are satellites with atomic reactors "up there" which
    >>will decay in the atmosphere for sure.
    An experimental nuclear reactor power system, the SNAP 10A which used
    thermoelectric power conversion, was launched by the United States in 1965 and
    worked satisfactorily for 43 days until shut down.  It is now in a very high
    orbit where it will remain for hundreds of years. Except for that one case, the
    use of nuclear sources for powering spacecraft built and launched by the United
    States been limited to very low power (less than 1/2 kW) systems called
    radioisotope thermoelectric generators (RTG). They do not use nuclear reactor
    heat sources. RTGs convert the heat generated by the decay of radioisotopes to
    electricity by using an array of thermocouples. Compared to a 1000-kilowatt
    reactor RTG's are extremely small,simple and safe. The fuel source in all U.S.
    RTGs has been plutonium-238.
    >>Who knows, how many reactors are up there?
    I'm not certain, but at last count I think it was about 48 RTG's.
    >>Embedded in what satellites?
    not sure of them all, I'll have to look it up later.
    >>Any plans to bring them back safely? :-)
    Of the RTGs launched by the US, there have been three mission malfunctions that
    I know of involving spacecraft which carried a total of four RTGs. One of these
    occurred in 1964 before the full fuel containment policy was initiated. This
    was the SNAP 9A RTG aboard a malfunctioning Navy spacecraft and it burned up in
    the upper atmosphere as designed. Since 1964, the design philosophy of full
    fuel containment has performed flawlessly in two mission failures involving
    RTGs. One landed intact in the Pacific Ocean in 1968 after a Nimbus B weather
    satellite failed to reach orbit.  The two generators were recovered and their
    fuel used in a subsequent mission.  In 1970, the Apollo 13 lunar module
    reentered the atmosphere and its RTG was jettisoned and fell intact into the
    Tonga Trench of the Pacific Ocean. In each case air and water samples taken in
    the reentry area indicate there was no release of radioactive material.
    >>How, in general, it was possible to solve the
    >>(veeery heavy) radiation shielding which made
    >>reactor driven aircrafts obsolete
    >>(because they where too heavy to lift off...)?
    No country was ever able to develop a true atomic-powered aircraft. But a
    nuclear plane of sorts did manage to fly, the NB-36H test airplane. Its
    original B-36H airframe had been extensively modified, most notably with a
    12-ton shielded crew capsule in the nose, a 4-ton lead disc shield in the
    middle and a number of large air intake and exhaust holes to cool the reactor
    in the aft section. The reactor was a 1000-kilowatt design weighing 35,000
    pounds. Its operation was observed from the crew capsule by closed circuit
    television. NB-36H flew with its radioactive cargo 47 times between 1955 and
    1957, and, although it did not power the airplane, the reactor provided
    considerable data on the effects of radiation emitted during flight. The test
    plane was eventually decommissioned at Fort Worth in late 1957. 
    Joe Hurley
    42.669575 -073.685737
    (Don't spam me, these are just the coordinates geocode spit out at me.)
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