What is a Radioisotope Power System?

Radioisotope power systems (RPS) convert heat generated by the natural decay of plutonium-238—a radioactive isotope—into electrical power. They have powered more than two dozen U.S. space missions and are capable of producing heat and electricity under the harsh conditions in deep space for decades without any maintenance.

Types of Radioisotope Systems

There are two types of radioisotope power systems:

Radioisotope Heater Units (RHU): Small devices that provide heat to keep a spacecraft’s electronic instruments and mechanical systems operational in the cold temperatures of our solar system.

Radioisotope Thermoelectric Generator (RTG): Flight-proven systems that provide power and heat to a spacecraft.

How Does an RTG Work?

RTGs work by converting thermal energy into electrical energy through devices known as thermocouples. The natural decay of plutonium-238 produces heat that is then transferred to one side of the thermocouple. The temperature difference between the fuel and the atmosphere allows the device to convert this heat into electricity. The most current RTG model, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), provides approximately 110 Watts of electrical power when freshly fueled.

RTGs are built to last. Its sturdy and compact design make it an ideal energy source for remote operations. They can withstand the harsh environments and frigid temperatures of deep space travel for decades, have no moving parts and require no maintenance, and have proven to be extremely reliable. In fact, some RTGs launched decades ago, are still in operation today like the Voyager mission that first started in 1977.