some of the space satellite concepts then being considered. By the mid-1950s the US had developed the basic design of a compact space reactor with hydrided zirconiumuranium alloy fuel elements coupled with liquid metal coolant for efficient heat transfer. The SNAP-2, SNAP-8 and SNAP-10A reactor power sources were developed from this basic design [1, 22, 23, 24]. Table III lists the major US space reactor programs, including both power and propulsion [23,24]. SNAP-10A, which was the first and so far only space reactor flown by the US, evolved from the SNAP-2 sodium-potassium (NaK)-cooled Rankine converter reactor and the SNAP-10 conduction-cooled thermoelectric converter reactor. In 1960, the US Air Force (USAF) and the US Atomic Energy Commission (AEC) initiated the Space System Abbreviated Development Plan for Nuclear Auxiliary Power Orbital Test (SNAPSHOT) Program. Under the program, the USAF was to furnish the launch and satellite vehicles and the AEC was to furnish the SNAP-10A reactor units. The reactor was to provide not less than 500 We with a 1-year operating lifetime [22]. Included among the objectives of the SNAP-10A/SNAPSHOT program were to: • Demonstrate, proof test, and flight qualify SNAP-10A for subsequent operational use; • Demonstrate the adequacy and safety of ground handling and launch procedures; and • Demonstrate the adequacy and safety of automatic reactor startup in orbit. As shown in Fig. 21, the completed SNAP-10A system had the shape of a truncated cone with an overall length of 3.48 m and a mounting base diameter of 1.27 m. This
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