Furthermore, this hazard is greatest just at launching when the unit is fresh. An isotope power supply using cerium 144, called Snap I, is in development. The Martin Co. is the prime contractor, with Thompson Products as subcontractor for the rotating conversion equipment. 17 Nuclear reactors have a criticality requirement which sets a lower limit to weight, and they may require more shielding. However, they do offer essentially an unlimited lifetime and less hazard at takeoff.
Reactors are attractive means for generation of large quantities of heat energy for very long times.
In the foreseeable future the weight of a large Installation based on a reactor source is likely to lie mostly in the machinery required to convert reactor heat into electricity. A reactor power supply called Snap II is also in development. The prime contractor is the Atomics International Division of North American Aviation. 18 See footnote 17. A polonium heat source can be used to heat a thermocouple to generate electricity.