With reference to radioisotope thermoelectric generators (RTGs), consider the following statements: 1. RTGs are miniature fission reactors. 2. RTGs are used for powering the onboard systems of spacecrafts. 3. RTGs can use Plutonium-238, which is a by-product of weapons development. Which of the statements given above are correct?

Let's analyze each statement regarding Radioisotope Thermoelectric Generators (RTGs): 1. **Statement 1 is incorrect.** RTGs are *not* miniature fission reactors. Fission reactors generate power through controlled nuclear chain reactions. RTGs, on the other hand, produce electricity by converting the heat generated from the *radioactive decay* of a suitable radioactive material (like Plutonium-238) into electricity using thermocouples. There is no controlled chain reaction involved. 2. **Statement 2 is correct.** RTGs are indeed widely used to power spacecraft, particularly those operating in deep space where solar power is insufficient (e.g., Voyager, Cassini, Perseverance rover). They provide a reliable, long-lasting power source for onboard systems, instruments, and communications. 3. **Statement 3 is correct.** RTGs typically use Plutonium-238 (²³⁸Pu) as their heat source. Plutonium-238 is a specific isotope of plutonium, which is *not* fissile and therefore not directly used in nuclear weapons (weapons primarily use Plutonium-239). However, ²³⁸Pu can be produced in nuclear reactors by irradiating Neptunium-237. The production of plutonium isotopes, in general, is related to nuclear programs, including those for weapons development or nuclear power, and thus ²³⁸Pu can be considered a by-product or associated with such programs, though it's distinct from weapons-grade material itself. The U.S., for instance, has restarted production of Pu-238 at national laboratories for RTG needs, using processes related to nuclear material handling. Therefore, statements 2 and 3 are correct.