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Comment by _ikke_ | Hacker News Reader

How long do we still expect data to come back from the voyagers? At some point the signal must be too weak to be able to pick up.

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IIRC the main limitation is the power supplies. They're failing slowly and they need to keep turning off instruments to allow it to keep running.

I believe it's expected that they'll need to pretty much turn off all of the instruments in the next 5 years, and after that it can run it's comms a bit longer but nothing else.

Edit: found an FAQ page from JPL about the Voyagers:

https://voyager.jpl.nasa.gov/frequently-asked-questions/

It looks like this year they need to start shutting down instruments more aggressively, expect to be able to run at least once instrument until 2025, and then there's a possibility of the voyagers staying contactable until 2036 with no instruments running.

I was just wondering why they would want to have a probe that can still run its comms equipment but can't return anything of scientific interest anymore because its instruments are no longer working... but then I realized that a nuclear power source is not like an ordinary battery - you can't use up more power now (e.g. to run the scientific instruments longer) and have less available later, you have a steadily declining "power budget" which would simply be wasted if not used?

Presumably the mere fact it can communicate and thus have its position and/or speed derived is itself of value.

It may also be valuable to have a way of testing how sensitive their earth-based receiving equipment is.

Not just testing but I'm sure a "known" signal coming from outside the solar system would be invaluable for developing and tuning deep space network systems.

Correct. The ability to determine distance and velocity allows the trajectory and dynamics of the instrument to be computed with high precision.

To see one application of this information, look for discussions of the "Pioneer Anomaly". That particular effect is now understood, but had it held up to detailed systematic-effect analysis, it would have affected our understanding of gravitation on solar-system scales.

When one enters entirely new territory, the understanding derived from single reliable measurements can be quite substantial.

That, and letting one instrument run and shutting down communication would probably be even less useful.

A check-in from a man-made object further out from Earth than ever achieved before is of scientific interest in itself.

The neat thing about the radio tech in question here is that while the signal continues to weaken, broadcast and reception tech keeps up with it. I don't know when (if) the curve runs out on that process, but we have a planet's worth of resources to bring to bear on the problem, as long as someone's willing to keep paying to upgrade the transceivers (and it's work that pays some nice side dividends in terms of being a convenient toy problem for testing new radio tech).

Since we know exactly what we're looking for and exactly where it should be, we have all kinds of neat radio tools to bring to bear on sampling a faint signal from interstellar noise.

What about sending a repeater station once in a while to follow them? Or would it be inefficient compared to constantly updating radio tech here on Earth?

Received radio power decreases as the square of the distance. If the repeater started now, to be useful it would have to be similarly large to the big radio telescopes used to receive the signal. It would need to have the same speed as the probe it was following to keep up the signal. But the Voyagers each were massively accelerated by their giant planet encounters. Launching a much-more-massive repeater at much higher initial velocity than the original probes is nonsensical.

Why would it have to be massive? In space, radio dishes can be unfolded mylar.

The point is it would be massive relative to the probes, and it would also have to be moving faster than them to be useful anytime soon. And if you could launch something that massive going that fast, why bother making it a repeater. Just launch a new probe with a bigger antenna.

Right, I am not sure the limiting factor here is our ability to send or interpret the received signals. I think the limiting factor that is most impactful is the probe itself.

Eventually, its power source will die out, its components will fail, or enough cosmic rays or debris will corrupt enough of its systems it can no longer transmit.

Given those factors, I do wonder what the expected lifetime of the probe is, with the power source being the most clear "game over" line.

Good point.

It appears that both Voyagers are slated to have some experiments disabled soon (2020 and 2021) to best use remaining power from the RTGs, but since the RTGs are nuclear sources, the decay rate is independent of power draw (it's more an issue of switching off the experiments to avoid peak draw killing the ship).

Voy1's expected to lose too much wattage to turn on the radio by 2025; I can't find a quick number for Voy2.

EDIT: It appears Voy2's power package was expected to allow mission operation through 2020, so sayeth Wikipedia; no idea if that implies the radio was expected to die this year or this was the year the craft would need to be reconfigured for a scaled-back mission profile to maintain enough power for attitude control and radio transmission.

The bigger problem is that they're powered by an RTG, which will soon cease to produce enough power to run the probes. They expect to start shutting down some of the few instruments still running next year, no longer have any power available for science around 2025, and run out of enough power to do radio transmission around 2030.

If the probes still had enough power by then, the current DSN would be able to receive data until the mid-2030's.

Rather than the radio signal being the limit, it's expected the power source will have diminished too much to power the instruments by 2030

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