Figure 4 Model of SNAP 50 power plant planned for deep space missions showing extensive waste heat radiator. The system will provide 300 to 1000 kilowatts of electrical power.
Carnot Efficiency
In 1824 Sadi Carnot, a young French engineer, conceived of an idealized heat engine. This ideal engine had an efficiency given by
e = 1 - Tc/Th = (Th - Tc)/Th
where
e = the so-called Carnot efficiency (no units)
Tc = the temperature of the waste heat reservoir (in degrees Kelvin, °K[4])
Th = the temperature of the heat source (in °K)
Unhappily, Tc cannot be made zero (and e therefore made equal to 1, which is 100% efficiency). Physicists have shown absolute zero to be unattainable, although they have approached to within a hundredth of a degree in the laboratory.