There are nuclear batteries that can run for 40 years without being charged. Some space missions run for years or even decades. They need reliable power to run scientific instruments and communications equipment. Nuclear batteries, so-called radio isotope power systems, provide energy for a very long time. Radio isotope power systems are thermoelectric devices. As opposed to reactors which run on nuclear fission, they use the decay of radioactive material to produce heat and electricity. The Mars Science Lab Curiosity is a mobile robot carrying a wealth of analytical instruments, and nuclear battery keeps curiosity running, even under the dire conditions of sandstorms on Mars. Its nuclear battery will power the rover's exploration for up to 15 years. The robotic spacecraft Cassini Huygens studied Saturn and entered the history books by descending to the surface of Titan, Saturn's largest moon. Its atomic battery kept its sensors and communications equipment working for more than 19 years until its mission ended. Voyager 1, another space probe, is the farthest operational spacecraft in human history and the only one to have entered interstellar space. After more than 40 years, its atomic batteries are keeping its scientific instruments running to explore the outer boundaries of the solar system and beyond.