Transuranic Elements in Space 

 Nuclear Power Systems 



THADDEUS J. DOBRY, JR. 



In the 20 years of the space age, the U. S. Department of Energy and its predecessors, the 

 U. S. Energy Research and Development Administration and the U. S. Atomic Energy 

 Commission, have liad a growing role in our country 's exploration and exploitation of 

 space. From a few early earth orbital missions through lunar landings to long-term 

 outer-planetary journeys, the safety, compactness, reliability, and life of nuclear isotope 

 power supplies fiave been essential to mission success. Technology improvements are 

 continuing to virtually eliminate the release of radioactive fuel during normal operations 

 and accident situations. 



Between June 1961 and December 1976 the United States launched 19 spacecraft 

 designed with electrical systems powered by the transuranic element plutonium, which 

 contained approximately 80% ^^^Pu and 17% ^^^Pu by weight. Of these 19 systems, 7 

 were U. S. Department of Defense (DOD) satelUtes and 12 were National Aeronautics and 

 Space Administration (NASA) scientific spacecraft (2 weather satelUtes, 6 Apollo lunar 

 experiments, 2 Pioneer interplanetary probes, and 2 Viking Mars landing vehicles). 

 Table 1 lists these launchings and gives the status of the systems. 



Of the 941,600 Ci of "^Pu (700 Ci of ^^^Pu) launched to date, 379,200 Ci (282 Ci 

 of ^^^Pu), approximately 40%o, is in long-term earth orbit. There is 222,500 Ci of ^^*Pu 

 (165 Ci of ^^^Pu), or approximately 24% of the total, on the lunar surface; 160,000 Ci 

 (119 Ci of ^^^Pu), approximately 17%o, has been ejected from our solar system, and 

 84,000 Ci (63 Ci of^^^Pu), 9% of the total, is on the surface of the planet Mars. The 

 remaining 10%, 95,900 Ci (71 Ci of ^^^Pu) was involved in three in-flight vehicle aborts. 



These aborts did not result in nuclear accidents and were of the following three types: 



1. The DOD Transit satellite 5 BN-3 launched in April 1964 from the Western Test 

 Range reentered the atmosphere, and the 17,000 Ci of ^^^Pu (13 Ci of ^^^Pu) promptly 

 burned up at high altitude over the Mozambique channel. Prior to 1967 plutonium metal 

 was used as a fuel, and burnup with subsequent atmospheric dilution was a design and 

 safety requirement. Since 1967 progress has been made in virtually eliminating reentry 

 burnup of the fuel in the event of an in-flight abort and in minimizing the probability of 

 releases of radioactive fuels from launch aborts. An intact reentry— intact impact 

 pliilosophy has been invoked to counter aborts leading to uncontrolled random 

 worldwide land or sea impacts. 



2. The NASA Nimbus B-1 weather satellite launched in May 1968 from the Western 

 Test Range was a range safety destruct action that resulted in the intact impact of 34,400 

 Ci of ^^^Pu (25 Ci of ^^^Pu) in the Santa Barbara channel. The fuel remained intact in 

 two containers, which were subsequently recovered. 



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