Radionuclide heating element

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Sectional view through a RHU heating element
Components of an RHU, a US 1 cent coin serves as a comparative figure .

Radionuclide heating elements are used in space travel and, by breaking down a small amount of a radionuclide, provide heat to heat cold-sensitive parts of a space probe , lander or rover .

Differentiation from radionuclide batteries

In contrast to radionuclide batteries , which are primarily used to generate electricity, the focus of heating elements is the decay heat from radioactivity. It is used to heat sensitive equipment (e.g. electronics) in spacecraft. Radionuclide batteries have a low degree of efficiency in converting the decay heat into electricity, but the unconverted part of the power can also be used for heating.

construction

The use of different radioisotopes is possible depending on the length of the mission, heat requirements and other criteria . The RHU (Radioisotope Heater Unit) manufactured by the United States each contain a pellet of 2.7 g of plutonium dioxide . This "fuel" is surrounded by a shell made of a platinum-rhodium alloy, which is in an insulation made of graphite and this in turn is in a heat shield made of the same material. The total mass of a single RHU, including the shield, is approximately 40 grams. A RHU is 3.2 cm long and 2.6 cm in diameter, the heat output is 1 watt .

use

In the cold outer solar system, space probes and landers often use radionuclide heating elements in cold-sensitive areas, even if they get their electrical energy from RTGs . In the case of battery-operated immersion and landing capsules in the outer solar system, the use of radionuclide heating elements has so far been the standard in order to prevent cooling. The battery power of these capsules is only sufficient for the relatively short measuring phase. In the inner solar system, landers and rovers on planets and moons use radionuclide heating elements in order not to cool down in the absence of solar radiation, even if they draw their energy from solar cells during the day . Battery systems for storing energy for heating during the night are often too heavy.

The Soviet Lunochod moon rovers used heating elements with Polonium 210 Po, while the American Mars rovers and probes used plutonium 238 Pu in their heating elements. The Chinese rover Yutu of the Chang'e-3 moon lander also uses plutonium 238 Pu in its heating elements so as not to cool down during the 14-day moon night.

Space applications of radionuclide heating elements
year Surname mission number Radioisotope
1969 15 watt RHU EASEP 2 238 Pu
1970 V3-R70-4 Lunochod 1 ? 210 Po
1972 RHU Pioneer 10 12 238 Pu
1973 V3-R70-4 Lunochod 2 ? 210 Po
1973 RHU Pioneer 11 12 238 Pu
1977 RHU Voyager 1 9 238 Pu
1977 RHU Voyager 2 9 238 Pu
1989 RHU Galileo Orbiter 103 238 Pu
1989 RHU Galileo rehearsal 17th 238 Pu
1996 RHU Mars Pathfinder Rover 3 238 Pu
1997 RHU Cassini orbiter 82 238 Pu
1997 RHU Huygens Lander 35 238 Pu
2003 RHU Spirit 8th 238 Pu
2003 RHU Opportunity 8th 238 Pu
2011 RHU Mars Science Laboratory ? 238 Pu
2013 ? Yutu ? 238 Pu

swell

  1. ↑ DOE: Radioisotope Heating Unit , accessed: May 24, 2012 ( Memento from August 5, 2012 in the web archive archive.today )
  2. ↑ http://www.bernd-leitenberger.de/luna.shtml Bernd Leitenberger: Das Luna Programm , accessed: May 24, 2012
  3. ↑ a b Günther Glatzel: Chang'e 3 on the way to the moon , in Raumfahrer.net, accessed December 1, 2013, date: December 3, 2013
  4. ↑ http://space.skyrocket.de/doc_sat/nuclear.htm Guenter's Space Page: Nuclear Powered Payloads , accessed: May 24, 2012
  5. ↑ http://solarsystem.nasa.gov/rps/rhu.cfm NASA: Radioisotope Power Systems, Radioisotope Heater Unit , accessed: May 24, 2012

Web links

Commons : RHU  - collection of pictures, videos and audio files