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

Correct Answer: (b) 2 and 3 only


  • Statement 1: RTGs are miniature fission reactors.
    • This statement is incorrect. RTGs are not fission reactors. They generate power through the natural radioactive decay of isotopes like plutonium-238, not through a fission chain reaction.
  • Statement 2: RTGs are used for powering the onboard systems of spacecrafts.
    • This statement is correct. RTGs have been used extensively to power the onboard systems of various spacecraft, including missions like Cassini, Voyager, and New Horizons.
  • Statement 3: RTGs can use Plutonium-238, which is a by-product of weapons development.
    • This statement is correct. Plutonium-238 is produced by irradiating neptunium-237, which can be recovered from research reactor fuel or special targets, and has been used in RTGs for space missions.

Learn more

  • Definition and Functionality:
    • Radioisotope Thermoelectric Generators (RTGs) are devices that convert heat released by the decay of radioactive materials into electricity using thermocouples. They are highly reliable and have no moving parts, making them ideal for long-duration missions in harsh environments.
  • Applications:
    • RTGs are primarily used in space missions where solar power is impractical. They have powered numerous missions, including the Apollo lunar landings, Viking Mars landers, Voyager probes, and the Cassini mission to Saturn.
  • Isotopes Used:
    • The most common isotope used in RTGs is plutonium-238 due to its high decay heat and relatively low gamma radiation, which requires minimal shielding. Americium-241 is another isotope used, particularly by the European Space Agency.
  • Safety and Design:
    • RTGs are designed with multiple safety features, including heat-resistant ceramic fuel forms, iridium capsules, and graphite blocks to contain the fuel and prevent its release in case of accidents. These features ensure that RTGs can withstand severe physical conditions.
  • Historical Context:
    • The first RTG was launched in 1961 aboard the Navy TRANSIT 4A Navigational Satellite. Since then, RTGs have been a crucial power source for many NASA missions, providing reliable power for decades.
  • Production Challenges:
    • The production of plutonium-238 is complex and was halted in the late 1980s. However, production resumed in 2015 at Oak Ridge National Laboratory to meet the needs of future NASA missions.

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