The heat motor can also be regarded as a kind of battery, and is used as a kind of energy source installed on artificial satellites, space probes and unmanned remote control equipment, such as the lighthouse built by the Soviet Union in the polar region, in some unmanned or no one can maintain to the place, to supply less than a hundred watts of electricity and the time needed is not available from the fuel cells, batteries, generators, and the solar cell can not be used in this place. When the radioisotope heat motor is the ideal energy source.
The principle is that the heat generated by the decay of the radioisotope plutonium-238 is directly converted to direct current by a thermocouple device to provide a variety of instruments and equipment. The half-life of the man-made isotope plutonium-238 is only 88 years, which means that its radioactivity decays quickly enough to make it very hot. And radioactive materials can continue to be hot for many years. Plutonium-238 emits alpha rays, which are easily blocked, and the material cannot be used in a nuclear bomb.
At a cost of $1.5 billion over the past 30 years, 330 pounds of plutonium-238 was produced at the U.S. National Laboratory in Idaho. Nuclear batteries made from Plutonium-238 can last for decades! Plutonium-238 produces a steady stream of heat that can be converted into electricity. Nuclear batteries made from Pu-238 can be a powerful source of energy for spacecraft, allowing them to continue flying and transmitting data in areas where the sun's rays are too dim. For example, the Cassini-Huygens probe used to explore Saturn and its moons.
The widely publicized nuclear-powered Mars rover Curiosity is powered by a radioisotope thermoelectric motor, model MMRTG, as shown in the table below.