Radioisotope heater unit
Radionuclide heating elements are used in the aerospace and deliver by the decay of a small amount of a radionuclide heat for heating temperature-sensitive parts of a spacecraft, a lander or a rover.
Function
Its function is to heat sensitive equipment items (eg electronics) in spacecraft is. This is more effective to use, as electric power is supplied from radionuclide. The reason is the low efficiency of conversion of the radionuclide in the decay heat to electrical energy. To provide enough electrical energy for heating, radionuclide would with a much larger amount of the expensive radionuclide needed than with the use of heating elements to the radionuclide cold-sensitive parts of the apparatus. For a radionuclide heating element the total heat capacity of the radionuclide is as useful heat for heating available. Depending on the mission length, heat requirement and other criteria, the use of various radioisotopes is possible.
Construction
The RHU manufactured by the United States ( radioisotopes Heater Unit) each containing a pellet of 2.7 g of plutonium. The " fuel " is surrounded by a sheath of a platinum -rhodium alloy, which is located in an insulation made of graphite, which in turn in a heat shield made of the same material. The total mass of a single RHU, including shielding, is about 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 spacecraft and lander often use at cold- sensitive sites radionuclide heating elements, even if they derive their electrical power from the RTGs. For battery-operated immersion and Lander capsules in the outer solar system, the use of radionuclide heating elements previously standard to prevent cooling. The battery power of these capsules ranges namely only for the relatively short measurement period. In the inner solar system Lander and Rover use on planets and moons radionuclide heating elements to avoid catching a chill in the absence of sunlight, even when daytime draw their energy from solar cells. Battery systems for storing the energy for heating during the night are often too heavy.
The heating elements used Soviet Lunokhod Moon Rover with polonium 210Po, the American Mars Rover and probes, however, use plutonium 238Pu in their heating elements. The Chinese Yutu Rover of the Chang'e -3 lunar landers used plutonium 238Pu in its heating elements to avoid catching a chill during the 14 - day lunar night.