Home > Radioisotope thermoelectric generator
A radioisotope thermoelectric generator (RTG) is a simple electrical generator which obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity using an array of thermocouples. RTGs can be considered as a type of battery and have been used as power sources in satellites, space probes and unmanned lighthouses.1 Design
The design of an RTG is simple by the standards of nuclear technology: the main component is a sturdy container of a radioactive material (the fuel). Thermocouples are placed in the walls of the container, with the outer end of each thermocouple connected to a heat sink. Radioactive decay of the fuel produces heat which flows through the thermocouples to the heat sink, generating electricity in the process.
A thermocouple is a thermoelectric device that converts thermal energy directly into electrical energy. It is made of two kinds of metal (or semiconductors) that can both conduct electricity. They are connected to each other in a closed loop. If the two junctions are at different temperatures, an electric current will flow in the loop.
The radioactive material used must have a relatively short half-life so that it decays quickly enough to generate a usable amount of heat. Typical half-lives for radioisotopes used in RTGs are a few decades and the most widely used fuel for RTGs is plutonium-238, in the form of plutonium oxide (PuO2).
2 Use
A common application of RTGs is as power sources on spacecraft, especially for probes that travel far enough from the Sun that solar panels are no longer viable. As such they are carried on Pioneer 10, Pioneer 11Saturn (artist's impression) Pioneer 11 was the second mission to investigate Jupiter and the outer solar system and the first to explore the planet Saturn and its main rings. Pioneer 11 (also called Pioneer G), like Pioneer 10, used Jupiter's mass in a g, Voyager 1The Voyager 1 spacecraft is an unmanned probe of the outer solar system. It is the most distant man-made object, still moving further away, and expected to keep on transmitting into the 2020s. It was originally planned as Mariner 11 of the Mariner program, Voyager 2The Voyager 2 spacecraft was launched in 1977, originally planned as Mariner 12 of the Mariner program. It is identical to its sister Voyager program craft, Voyager 1. Voyager 2 followed a somewhat different trajectory during its Saturn encounter, however, Galileo, UlyssesUlysses is an unmanned probe designed to study the Sun at all latitudes. The spacecraft, named for the Latin translation of " Odysseus", was launched in October 1990 from the Space Shuttle Discovery (mission STS-41) as a joint venture of NASA and the Euro and CassiniCassini-Huygens is a joint NASA/ ESA unmanned space mission intended to study Saturn and its moons. The spacecraft consists of two main elements: the Cassini orbiter and the Huygens probe . It was launched on October 15, 1997 and entered Saturn's orbit on. As well as this, RTGs were used to power the two VikingViking refers in a loose sense to the North Germanic (ethnically Scandinavian) population of Northern Europe in the 8th, 9th, 10th and 11th centuries, which during this time colonized, raided and traded the lengths of the coasts, rivers and islands of Eur landers and for the scientific experiments left on the moon by the crews of Apollo 12– 17. RTGs were also used by the Americans for Nimbus, Transit and Les satellites.
In addition to spacecraft, the Soviet Union constructed many unmanned lighthouses and navigation beacons powered by RTGs (see Bellona's report). These now pose environmental and security concerns, as leakage or theft of the radioactive material could pass unnoticed for years (or possibly forever; some of these lighthouses cannot be found because of poor record keeping).
In the past, small "plutonium cells" — essentially "micro-RTGs" — have been used in implanted heart pacemakers to ensure a very long "battery life". Although not strictly RTGs, small samples of radioactive material called radioisotope heater units are also used by various spacecraft for heating including the Mars Exploration Rovers, Galileo and Cassini.
