NASA works in partnership with DOE to maintain the capability to produce the Multi-Mission Radioisotope Thermoelectric Generator (or MMRTG) and to develop higher-efficiency energy conversion technologies, such as more efficient thermoelectric converters as well as Stirling converter technology.
Radioisotope power systems—abbreviated RPS—are a type of nuclear energy technology that uses heat to produce electric power for operating spacecraft systems and science instruments. That heat is produced by the natural radioactive decay of plutonium-238.
This website offers a variant no. of quiz and pledges certificate. Today is the day for NASA “Scientist for a Day”. You can generate an electronic certificate of participation on their page