Correct Option
Statement 2 is correct. Radioisotope Thermoelectric Generators (RTGs) are extensively used to power spacecraft, particularly for long-duration missions and deep space probes where solar energy is insufficient or unreliable. They convert heat generated from radioactive decay directly into electricity using thermocouples, offering a reliable power source without moving parts, suitable for harsh environments. Examples include the Voyager probes, Cassini, Galileo, and Mars rovers.
Statement 3 is correct. Plutonium-238 (Pu-238) is the primary radioisotope fuel used in most RTGs. It undergoes alpha decay, releasing heat that is then converted into electrical energy. While Pu-238 itself is not a fissile material used in nuclear weapons, its production often occurs in nuclear reactors that can also be involved in nuclear weapons programs, making it a by-product or co-product of such facilities.
Incorrect Options
Statement 1 is incorrect. RTGs are not miniature fission reactors. Fission reactors operate by controlling a nuclear chain reaction where heavy atomic nuclei (like Uranium-235 or Plutonium-239) are split, releasing a large amount of energy. In contrast, RTGs generate heat through the natural process of radioactive decay (specifically alpha decay) of an unstable isotope like Plutonium-238, without involving a chain reaction or nuclear fission.