NASA engineers have started loading nuclear fuel into the Mars 2020 rover. In anticipation of the unmanned explorer's scheduled 2020 launch, the space agency's Associate Administrator for the Science Mission Directorate, Thomas Zurbuchen, has given the green light to begin placing the plutonium-238 dioxide fuel into the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) that will provide the rover with heat and electricity.

Built under the auspices of the United States Department of Energy's (DOE) Office of Space and Defense Power Systems, the MMRTG isn't a nuclear reactor, but more of a nuclear battery. Specifically, it generates 110 watts of power through the natural decay of the plutonium-238 radioactive isotope set in eight General-Purpose Heat Source (GPHS) modules.

Most of the heat from these is converted into electricity through thermal conductors to power the rover's experiments, electronics, robotic arm, and wheels. Meanwhile, the excess heat is channeled to keep the spacecraft warm during the freezing Martian night.

Over 27 nuclear power systems have been used by US space missions, though the MMRTG is a more recent innovation, with the first installed in NASA's Curiosity Mars rover. Though production of the isotope has been restarted, the United States currently has enough plutonium to build two more MMRTGs after the Mars 2020, however these have not been assigned.

NASA says that the fueling is being carried out by the DOE and will be completed before the July 2020 launch date when it will lift off from Cape Canaveral Air Force Station in Florida. The rover will then land autonomously on February 18, 2021 at Jezero Crater in the Syrtis Major region of Mars.

Source: NASA

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