What's the power of the signal by the time it gets to Voyager?
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Yeah, I was just wondering what the signal strength at the antenna was and what kind of codec is used for error correction, etc. I'm assuming the SNR must be insanely low.
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You can get some of that information from DSN Now: eyes.nasa.gov/dsn/dsn.html
For instance a dish at Tidbinbilla in Australia is currently talking to & you can see the data rate & power from the downlink. Can't remember if it shows transmit power when sending.
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For the bits that aren't covered by DSN Now. The Voyagers use a multi convolutional encoding 1/2, this means that there are double the symbols to the actual bits. You theoretically get a 3db improvement between the symbol and bit SNR. A SSNR above zero gives good telemetry.
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Thanks Richard this is super helpful and interesting. One last question for you -- I am assuming the power on Voyager will fail before distance becomes a problem to send / receive data?
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Correct, but the 2 are sort of linked because they follow the same timeline. The power generated by the RTG continues to deplete as the spacecraft free space path loss keeps increasing as it travels further and further.
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"Each MHW-RTG contains 24 pressed plutonium-238 oxide spheres."
Damn, I just realized how much time has passed since that RTG was first made. Wow.
Thanks again for your excellent answers!
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I think the the use of pu-238 as heaters is also very clever. Each Radioisotope Heater Unit (RHU) produces 1Watt of heat, The Voyagers have 9 each. They've been throwing them into spacecraft since the 60s to prevent freezing of critical components
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I remember reading a year or two ago that NASA was actually very low on pu-238 for future units. I can't remember where they are sourced from but I believe one country was Russia.
I'm not sure if the US currently has a larger supply or not. Doesn't the Mars Rover use one?
The US started production again in 2011 and now NASA funds the
Department of Energy (DOE) to produce it.