The US equivalent to a Soviet Union satellite equipped with a nuclear reactor is the radioisotope thermoelectric generator or RTG. An RTG is a nuclear reactor type electrical generator. The heat released from the radioactive decay of a specified radioactive element in the device is converted into electricity and used for power.
Thus, RTGs can be considered as a type of battery, and have been used as power sources in satellites, space probes and other unmanned remote facilities (such as a series of lighthouses built by the former Soviet Union inside the Arctic Circle).
RTGs are used where solar cells are not practical and power usage is longer than that which can be provided by fuel cells. A common application of RTGs is as power sources on spacecraft such as Voyager 1, Voyager 2 and Galileo. In addition, RTGs were used to power scientific experiments left on the Moon by the crews of Apollo 12 through 17 (except Apollo 13, as we will see).
RTGs may pose a risk of radioactive contamination: if the container holding the fuel leaks, the radioactive material may contaminate the environment. For spacecraft, the main concern is that if an accident were to occur during launch or a subsequent passage of a spacecraft close to Earth.
One such incident took place on April 21, 1964, when a Transit-5BN-3 navigation satellite failed to reach orbit when launched. The spacecraft burned up over Madagascar and the plutonium fuel in the RTG was injected into the atmosphere over the Southern Atlantic Ocean. Traces of the Plutonium were detected in the atmosphere as a result.
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