UPSC Prelims 2024 Q31: Science & Technology – Energy & Environment
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
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer: (b) 2 and 3 only
Explanation
Radioisotope Thermoelectric Generators (RTGs)
| Statement | Verdict | Fact |
|---|---|---|
| 1. Miniature fission reactors | Wrong | RTGs use the natural radioactive decay of an isotope; there is no chain reaction |
| 2. Power spacecraft systems | Correct | Used on Voyager 1 and 2, Cassini, New Horizons, and the Mars rovers Curiosity and Perseverance |
| 3. Can use Plutonium-238, a by-product of weapons work | Correct | Pu-238 was produced in reactors built for nuclear weapons programmes |
How an RTG works:
| Step | What happens |
|---|---|
| Decay heat | Pu-238 gives off heat as it decays (half-life about 88 years) |
| Thermocouples | Turn the temperature difference into electricity (Seebeck effect) |
| Advantage | No moving parts; works for decades where sunlight is too weak |
Answer: (b) 2 and 3 only.
Why each option is right or wrong
- (a) Incorrect. Statement 1 is false; RTGs run on decay heat, not nuclear fission.
- (b) CORRECT. RTGs power deep-space probes and can run on Pu-238, a by-product of weapons programmes.
- (c) Incorrect. It includes the false Statement 1 and leaves out the true Statement 2.
- (d) Incorrect. Statement 1 is false, so 'all three' fails.
Key point
RTG = decay heat of Pu-238 turned into electricity by thermocouples; no fission. Powers Voyager, Cassini, Curiosity.
Remember
RTGs turn plutonium-238 decay heat into electricity for deep-space probes.
Common mistakes
- Calling RTGs reactors; there is no chain reaction, only steady radioactive decay.
- Confusing weapons-grade Pu-239 with Pu-238, which is used in RTGs.
- Thinking solar panels can power probes to the outer planets; sunlight there is too weak.
Exam tip
Reactor = fission chain reaction; RTG = decay heat + thermocouple. That single difference settles Statement 1.
Sources
- NASA — Radioisotope Power Systems (rps.nasa.gov)
- US Department of Energy — Plutonium-238 production programme