Радиоактивты ыдырау арқылы жылу беретін құрылғы

Device that provides heat through radioactive decay

A radioisotope heater unit (RHU) is a small device that provides heat through radioactive decay. They are similar to tiny radioisotope thermoelectric generators (RTG) and normally provide about one watt of heat each, derived from the decay of a few grams of plutonium 238—although other radioactive isotopes could be used. The heat produced by these RHUs is given off continuously for several decades and, theoretically, for up to a century or more. In spacecraft, RHUs are used to keep other components at their operational temperatures, which may be very different to the temperature of other parts of the spacecraft. In the vacuum of space any part of the spacecraft which doesn't receive direct sunlight will cool down so much that electronics or delicate scientific instruments break down. They are simpler and more reliable than other ways of keeping components warm, such as electric heaters.

Radioisotope heater units for NASA missions have used Plutonium 238 as the isotope for heat sources, since the radioactive half life of 87.7 years means that the decay of the isotope will not limit the mission lifetime. The isotope produces 0.57 watts of thermal power per gram of 238Pu. Soviet missions have used other isotopes, such as the Polonium 210 heat source used in the Lunokhod lunar rovers. With a half life of about 4 1⁄2 months, Po 210 produces more thermal power per unit mass, but is suitable only for shorter duration missions. Strontium 90 has also been proposed.

While both RHUs and Radioisotope Thermoelectric Generators (RTGs) use the decay heat of a radioactive isotope, RHUs are generally much smaller as a result of omitting the thermocouples and heat sinks/radiators required to generate electricity from heat. Both RHUs and RTGs feature rugged, heat resistant casings to safely contain the radioisotope in the event of a launch or re entry vehicle failure. The total mass of a single one watt RHU (including shielding) is about 40 grams. Similar schemes, such as thermionic generators, have also been used.

The United States Department of Energy has developed the general purpose heat source (GPHS) primarily for space use. These GPHSs can be used individually or in groups of up to eighteen for component heating, but are primarily used as the heat source for RTGs. Each GPHS contains four iridium clad Pu 238 fuel pellets, standing 5 cm tall, 10 cm square and weighs 1.44 kg.