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Truly incredible that two probes built and launched 35 years ago are still functioning at all, let alone extending their mission and literally expanding our sph

Truly incredible that two probes built and launched 35 years ago are still functioning at all, let alone extending their mission and literally expanding our sphere of scientific understanding. When I see NASA spacecraft doing such extraordinary things, long beyond their expected lifespan, I always feel a little guilty when a simple function I wrote can't even process a test file without crashing!

rosser 13y ago
Surprisingly, according to the Wikipedia article on RTGs (Radioisotope Thermoelectric Generators, the power source for the Voyager probes), by 2001, the probes' RTGs were down to 67% of capacity, instead of the 83-and-change percent expected. [1] So, while still impressive, they're unfortunately not working as well as they could be. [1] https://en.wikipedia.org/wiki/Radioisotope_Thermoelectric_Generator#Life_span https://en.wikipedia.org/wiki/Radioisotope_Thermoelectric_Ge...
- anonymfus 13y ago
  >However, the bi-metallic thermocouples used to convert thermal energy into electrical energy degrade as well Are there copies of these RTGs on Earth for analyst or it was defined by lack of any other explanation?
  - jevinskie 13y ago
    I think it is likely. I was under the impression that space programs try to keep identical subsystems on Earth so they can use them to debug in-mission issues. Hard to attach a JTAG debugger when your device under test is 34 lighthours away! =)
    - pepve 13y ago
      34 hours is the roundtrip time, the distance is 17 light hours.
      - jevinskie 13y ago
        Thank you, I didn't catch that.
- InclinedPlane 13y ago
  They're working just as well as expected. There are three factors that reduce the output of an RTG over time. The first, and most obvious, is the radioactive decay of the fuel source. (As an aside, potentially this can be more complicated than one might think because as the primary isotope decays it builds up other radioactive isotopes which also produce heat and have different half-lives, so you need to solve a series of differential equations to determine the heat output over time, but for Pu-238 it's actually fairly simple since the main decay product is a much longer lived isotope, U-234) Anyway, the half-life of Pu-238 is about 88 years, so you'd expect it would take about that long for the heat output of the RTG to drop by half. However, the radioactivity of the RTG fuel source also degrades the thermocouples used to generate electricity over time, and this reduces the power output on top of the decay of the fuel. Additionally, as the amount of Pu-238 remaining falls the amount of heat generated by it also falls, lowering the temperature of the RTG and reducing the Carnot efficiency of the device, though only marginally.

rosser 13y ago

Surprisingly, according to the Wikipedia article on RTGs (Radioisotope Thermoelectric Generators, the power source for the Voyager probes), by 2001, the probes' RTGs were down to 67% of capacity, instead of the 83-and-change percent expected. [1] So, while still impressive, they're unfortunately not working as well as they could be. [1] https://en.wikipedia.org/wiki/Radioisotope_Thermoelectric_Generator#Life_span https://en.wikipedia.org/wiki/Radioisotope_Thermoelectric_Ge...

anonymfus 13y ago
>However, the bi-metallic thermocouples used to convert thermal energy into electrical energy degrade as well Are there copies of these RTGs on Earth for analyst or it was defined by lack of any other explanation?
- jevinskie 13y ago
  I think it is likely. I was under the impression that space programs try to keep identical subsystems on Earth so they can use them to debug in-mission issues. Hard to attach a JTAG debugger when your device under test is 34 lighthours away! =)
  - pepve 13y ago
    34 hours is the roundtrip time, the distance is 17 light hours.
    - jevinskie 13y ago
      Thank you, I didn't catch that.
InclinedPlane 13y ago
They're working just as well as expected. There are three factors that reduce the output of an RTG over time. The first, and most obvious, is the radioactive decay of the fuel source. (As an aside, potentially this can be more complicated than one might think because as the primary isotope decays it builds up other radioactive isotopes which also produce heat and have different half-lives, so you need to solve a series of differential equations to determine the heat output over time, but for Pu-238 it's actually fairly simple since the main decay product is a much longer lived isotope, U-234) Anyway, the half-life of Pu-238 is about 88 years, so you'd expect it would take about that long for the heat output of the RTG to drop by half. However, the radioactivity of the RTG fuel source also degrades the thermocouples used to generate electricity over time, and this reduces the power output on top of the decay of the fuel. Additionally, as the amount of Pu-238 remaining falls the amount of heat generated by it also falls, lowering the temperature of the RTG and reducing the Carnot efficiency of the device, though only marginally.