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A suggestion has been made that the Voyagers may run out of propellant and so may not be able to maintain pointing near the Earth for communications.

According to @BowlOfRed's answer:

Although the craft can be turned if necessary, the voyager probes are not intentionally rotating. They use small thrusters that try to zero out any rotations.

These thrusters aren't infinitely precise, nor are the instruments that drive them. So there is some error in the firing that means the probe has a (small) residual rotation. Instead of having a perfectly fixed direction, it will slowly drift away from the intended attitude over time. When the residual rotation moves the platform too far from the antenna pointing at earth, the thrusters fire to to return the alignment.

With what little remains of the Voyagers' cold gas thruster propellant, could the spacecraft be given a slight rotation in order to approximately stabilize one axis of their attitude?

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uhoh
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  • IIRC the animations for the Voyager probes always showed them spinning, not sure why. – GdD May 08 '19 at 11:39
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    You are making 2 assumptions: 1) spin stabilization would be accurate enough to reduce propellant use and 2) spin stabilization would reduce propellant use. – GdD May 08 '19 at 11:42
  • Save on solar power @uhoh? I don't get that. Was it a barbecue roll? – GdD May 08 '19 at 12:14
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    One question to consider is the symmetry of the spacecraft - it's been too long since I've studied classical mechanics, but I recall an exercise about principal axes and stability. Think of a book: if you throw it upwards spinning so that the spine traces out a circle, it will keep that orientation, but if you spin it around the other long axis it will start tumbling. – llama May 08 '19 at 18:33
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    Ah, there's a name for it: The tennis racket theorem https://en.wikipedia.org/wiki/Tennis_racket_theorem – llama May 08 '19 at 18:35
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    @llama that's the kind of direction that I'd originally hoped this question to go, I'll ping you when I post it. Thanks! update: it's not a tennis racket, but here's a video of just that, made in space: https://youtu.be/fPI-rSwAQNg Now I've just asked Have there been any Foucault pendulum demonstrations in space? – uhoh May 09 '19 at 01:18

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There is enough hydrazine to last beyond the end of the mission, about 25% of total tank volume is still available. From Descanso volume 4, you can see enough hydrazine for attitude control is available to last until 2040/2048:

Spacecraft lifetime estimates

As in all communications around the end of life for Voyager operations, this lifetime estimate considers the mission to end when there's no longer enough power to run any of the science instruments and/or the transmitter and keep the spacecraft alive.

The mission objective of the VIM is to obtain useful interplanetary, and possibly interstellar, fields, particles, and waves (FPW) science data until year 2020 and beyond when the spacecraft's ability to generate adequate electrical power for continued science instrument operation will come to an end.

I have found no references to spin stabilization as an option for Voyager operations: because of the above, the Voyager team never had to consider spin stabilization.

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  • The sources that you cite in this answer could help to answer this question: https://space.stackexchange.com/q/36001/26446 – DrSheldon May 08 '19 at 15:49