Sanman, to add to above - (Use of RHU or RTG is quite common) -- except of earth orbits etc, one uses it for longer space voyages..
For those interested in technical details and physics background .. etc.. please keep reading.
Most NASA space probes have used Radioisotope Heater Units (RHUs) or Radioisotope Thermoelectric Generators (RTGs) to provide power and heat. RTGs use the heat generated by the radioactive decay of plutonium-238 to power spacecraft and keep their instruments warm...RHUs generally are there to keep electronics warm..(RHU are small - do not have thermocouples etc to generate electricity/power(
NASA has used RHUs or RTGs on over 50 space missions - starting in 1970's , including:
The Voyager 1 and 2 probes, which are still traveling through interstellar space
The Cassini-Huygens mission to Saturn and Titan
The Galileo mission to Jupiter
The Ulysses mission to the Sun's poles
The Mars Exploration Rovers Spirit and Opportunity
The New Horizons mission to Pluto and the Kuiper Belt
The James Webb Space Telescope
RHUs and RTGs are essential for missions to deep space or to planets and moons with cold environments.
They are also used on some Earth-orbiting satellites and planetary landers.
According to NASA's RPS website, over 300 RHUs have been launched on a variety of NASA spacecraft. RTGs are larger and more powerful than RHUs, and are typically used on missions where more power is needed.
The same is true for Russian (or Soviet Union) - again *many* dozens probes...
Eg: Venera 9 and 10 (first spacecraft to land on Venus)
Luna 16 and 20, which returned samples of lunar soil to Earth
Phobos 1 and 2, which were missions to Mars
Mars 96, which was a failed mission to Mars
Phobos-Grunt, which was a failed mission to Phobos..
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Chinese are using it on same scale - (Chang'e 5-T, Tianwen-1 etc).. they did not (from what I know) have technology to produce Pu-238 before and were depending on others.. but now they (CAST - China Academy of Space Technology) said that they have successfully developed a prototype RTG using Chinese-made plutonium-238. This is a significant development, as it means that China will no longer need to rely on foreign suppliers for RTGs.
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India can produce its own plutonium-238 (Pu-238). BARC has developed a prototype radioisotope thermoelectric generator (RTG) using Pu-238, which is designed to be used on Chandrayaan type lunar orbiter.
India is strong in nuclear research and development, and it is one of the few countries in the world that can produce Pu-238. BARC has a dedicated Plutonium-238 Production Plant (P-238PP), which is used to produce Pu-238 for space applications.
The P-238PP uses a process called neutron irradiation to produce Pu-238. In this process, enriched uranium-238 is irradiated with neutrons in a nuclear reactor. This causes some of the uranium-238 atoms to absorb neutrons and transmute into Pu-238.
I have an earlier post in this dhaga about RHU - and India's status, and some ISRO slides..
(As I said earlier, Pu-238 producing is a little challenging task, Pu238 is different than Pu -239 used for 'other' purposes..)
Hope this is interesting to some folks here..
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Adding an old slide from a post earlier: