Editing Radioisotope heater unit (section)

{{Short description|Device that provides heat through radioactive decay}}
{{redirect|RHU|the village|Rhu}}
{{redirect|RHUs|the commune|Épiais-Rhus|the plant|Rhus}}
{{more citations needed|date=December 2018}}
[[Image:Radioisotope heater unit.gif|thumb|Diagram of a radioisotope heater unit]]

A '''radioisotope heater unit''' ('''RHU''') is a small device that provides heat through [[radioactive decay]].<ref>NASA (2016). [https://rps.nasa.gov/system/downloadable_items/31_Final_RHU_Fact_Sheet_2016_5-26-16.pdf Radioisotope Heater Units], NASAFacts. Retrieved 23 June 2022.</ref> They are similar to tiny [[radioisotope thermoelectric generator]]s (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.<ref name=doe1>{{Cite web  | title = Department of Energy Facts: Radioisotope Heater Units
  | publisher = U.S. Department of Energy, Office of Space and Defense Power Systems  | date = December 1998   | url = https://saturn.jpl.nasa.gov/system/downloadable_items/291_rhu.pdf | archive-url = https://web.archive.org/web/20160810043227/https://saturn.jpl.nasa.gov/system/downloadable_items/291_rhu.pdf | url-status = dead | archive-date = 2016-08-10 | access-date = March 24, 2010}}</ref>

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.<ref name=doe1/>