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 ?

(a) 1 and 2 only
(b) 2 and 3 only ✓ UPSC's answer
(c) 1 and 3 only
(d) 1, 2 and 3

Why the answer is (b)

• An RTG converts the heat of natural radioactive decay directly into electricity using thermocouples (the Seebeck effect); there is no chain reaction, so statement 1 calling them 'miniature fission reactors' is wrong.

• Statement 2 is correct: RTGs power deep-space probes and rovers where sunlight is too weak for solar panels — Voyager, Cassini, New Horizons, Curiosity and Perseverance all use them.

• Statement 3 is correct: the preferred fuel is plutonium-238, which is produced in reactors as a by-product of nuclear-weapons and isotope programmes, has an 88-year half-life and emits mainly alpha particles that are easy to shield.

• RTGs are reliable for decades but low in power (a few hundred watts).

• Hence 2 and 3 only, option (b).

Why the other options are wrong

(a) 1 and 2 only: Statement 1 is wrong: RTGs rely on radioactive decay, not fission.
(c) 1 and 3 only: Statement 1 is wrong; statement 2 on spacecraft use is correct.
(d) 1, 2 and 3: Statement 1 is wrong, so all three cannot be correct.

Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2024, held on 16 June 2024. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.