3 ms·

Thanks. Your comment sent me to Wikipedia, where I found this related snippet: > In the year 2000, 23 years after production, the radioactive material inside t

Thanks. Your comment sent me to Wikipedia, where I found this related snippet: > In the year 2000, 23 years after production, the radioactive material inside the RTG had decreased in power by 16.6%, i.e. providing 83.4% of its initial output; starting with a capacity of 470 W, after this length of time it would have a capacity of only 392 W. A related loss of power in the Voyager RTGs is the degrading properties of the bi-metallic thermocouples used to convert thermal energy into electrical energy; the RTGs were working at about 67% of their total original capacity instead of the expected 83.4%. By the beginning of 2001, the power generated by the Voyager RTGs had dropped to 315 W for Voyager 1. There's also a nice picture of one deployed on the moon. The dust on the moon's surface looks spectacular in that picture. https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

tutfbhuf 6y ago
How much Watt do they have now 20 years later in 2021?
- chias 6y ago
  I can give you half an answer and speculation on the other half. Given that radioisotopes decay with a halflife pattern, I would expect that you'd see a 16.6% drop in capacity every 23 years. So something like: 1977: 100% (470 W) 2000: 83.4% (392 W) 2023: 69.6% (327 W) To get a full answer, you'd need to know how the thermocouples degrade. Under the (completely unsubstantiated) assumption that they degrade linearly, that's about a 20% efficiency degradation per 23 years: 1977: 100% isotope * 100% coupling efficiency -> 470 W (100% of capacity) 2000: 83.4% isotope * 80% coupling efficiency -> 314 W (67% of capacity) 2023: 69.6% isotope * 60% coupling efficiency -> 196 W (41% of capacity) I suspect the thermocouple efficiency degradation is very much non-linear -- or rather, I have no reason to actually expect it to be linear -- so the second half of the above is a total SWAG, but maybe gives you a rough idea :)
st_goliath 6y ago
> There's also a nice picture of one deployed on the moon. That was also one of the many issues that cropped up during Apollo 13. They too had an RTG on board that was supposed to stay on the moon[1]. According to the book "Lost Moon" by Lovell and Kluger, a potential explosion of the Saturn V during launch was accounted/planned for, but the RTG "coming home" together with the LEM wasn't. IMO the book was a bit hazy on how that situation was addressed exactly, but according to Wikipedia that RTG is currently resting somewhere deep in the Pacific[2]. Also an interesting read on that topic is the SNAP program itself that developed the technology in the first place, even shot entire mini-nuclear-reactors into earth orbit[3] and resulted in some stereotypical 1960s nuclear safety shenanigans/mishaps during testing[4][5]. [1] https://en.wikipedia.org/wiki/Apollo_13#Experiments_and_scientific_objectives https://en.wikipedia.org/wiki/Apollo_13#Experiments_and_scie... [2] https://en.wikipedia.org/wiki/Apollo_13#Reentry_and_splashdown https://en.wikipedia.org/wiki/Apollo_13#Reentry_and_splashdo... [3] https://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_Power https://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_... [4] https://en.wikipedia.org/wiki/SNAP-10A#Safety https://en.wikipedia.org/wiki/SNAP-10A#Safety [5] https://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_Power#SNAP-9 https://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_...

tutfbhuf 6y ago

How much Watt do they have now 20 years later in 2021?

chias 6y ago
I can give you half an answer and speculation on the other half. Given that radioisotopes decay with a halflife pattern, I would expect that you'd see a 16.6% drop in capacity every 23 years. So something like: 1977: 100% (470 W) 2000: 83.4% (392 W) 2023: 69.6% (327 W) To get a full answer, you'd need to know how the thermocouples degrade. Under the (completely unsubstantiated) assumption that they degrade linearly, that's about a 20% efficiency degradation per 23 years: 1977: 100% isotope * 100% coupling efficiency -> 470 W (100% of capacity) 2000: 83.4% isotope * 80% coupling efficiency -> 314 W (67% of capacity) 2023: 69.6% isotope * 60% coupling efficiency -> 196 W (41% of capacity) I suspect the thermocouple efficiency degradation is very much non-linear -- or rather, I have no reason to actually expect it to be linear -- so the second half of the above is a total SWAG, but maybe gives you a rough idea :)

st_goliath 6y ago

> There's also a nice picture of one deployed on the moon. That was also one of the many issues that cropped up during Apollo 13. They too had an RTG on board that was supposed to stay on the moon[1]. According to the book "Lost Moon" by Lovell and Kluger, a potential explosion of the Saturn V during launch was accounted/planned for, but the RTG "coming home" together with the LEM wasn't. IMO the book was a bit hazy on how that situation was addressed exactly, but according to Wikipedia that RTG is currently resting somewhere deep in the Pacific[2]. Also an interesting read on that topic is the SNAP program itself that developed the technology in the first place, even shot entire mini-nuclear-reactors into earth orbit[3] and resulted in some stereotypical 1960s nuclear safety shenanigans/mishaps during testing[4][5]. [1] https://en.wikipedia.org/wiki/Apollo_13#Experiments_and_scientific_objectives https://en.wikipedia.org/wiki/Apollo_13#Experiments_and_scie... [2] https://en.wikipedia.org/wiki/Apollo_13#Reentry_and_splashdown https://en.wikipedia.org/wiki/Apollo_13#Reentry_and_splashdo... [3] https://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_Power https://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_... [4] https://en.wikipedia.org/wiki/SNAP-10A#Safety https://en.wikipedia.org/wiki/SNAP-10A#Safety [5] https://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_Power#SNAP-9 https://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_...