A radioisotope thermoelectric generator (RTG, RITEG), also known as a radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the heat released by radioactive decay into electricity via the Seebeck effect. It is a type of power source that uses the thermoelectric effect to convert the heat produced by radioactive decay of isotopes into electricity. There are no moving parts in this generator. It is commonly used in situations requiring long-lasting and dependable power sources, such as space missions, remote weather stations, and deep-sea exploration.
RTGs are ideal for remote and harsh environments for extended periods of time because they do not require solar energy, and because they have no moving parts, there is no risk of parts wearing out or malfunctioning. RTGs are typically the most desirable power source for unmaintained situations that require a few hundred watts (or less) of power for periods of time that are too long for fuel cells, batteries, or generators to provide economically, and in locations where solar cells are not practical. RTGs have been used as power sources in satellites, space probes, and unmanned remote facilities such as the Soviet Union’s series of lighthouses built inside the Arctic Circle.
RTG safety requires radioisotope containment long after the unit’s productive life. RTGs are expensive, which limits their use to niche applications in rare or special situations.
Here’s how an RTG typically works:
- Isotope Selection: RTGs employ isotopes with a long half-life, which means they decay slowly over time. Because of its favorable decay properties, plutonium-238 (Pu-238) is the most commonly used isotope.
- The chosen isotope undergoes radioactive decay, emitting high-energy alpha particles. As the isotope decays, heat energy is released as a byproduct.
- Heat Conversion: The heat produced by the decay process is transferred to a series of thermocouples made of various materials with different electrical properties. The difference in temperature between the thermocouples causes an electric potential difference.
- Thermoelectric Effect: The Seebeck effect produces an electric current from the electric potential difference generated by the thermocouples. The Seebeck effect occurs when the temperature difference between two dissimilar conductors causes an electric current to flow in a closed circuit.
- Electricity Generation: The thermoelectric effect generates an electric current, which is then used to power electrical devices or charge a battery for later use. The output power of an RTG is determined by the isotope’s decay rate and the efficiency of the thermoelectric materials used.
RTGs are known for their long lifespan and durability, often providing power for several years or even decades. They are not reliant on sunlight or other external factors, making them appropriate for use in space exploration missions where sunlight may be scarce. RTGs were used to provide electrical power for the Voyager and Pioneer spacecraft, as well as the Mars rover missions (such as Curiosity and Perseverance).
