# Could the Voyager spacecraft be spin-stabilized to keep their high gain antennas pointing towards the Sun (and therefore Earth)?

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.

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?

• IIRC the animations for the Voyager probes always showed them spinning, not sure why.
– GdD
May 8, 2019 at 11:39
• 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 8, 2019 at 11:42
• 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. May 8, 2019 at 18:33
• Ah, there's a name for it: The tennis racket theorem en.wikipedia.org/wiki/Tennis_racket_theorem May 8, 2019 at 18:35
• @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: youtu.be/fPI-rSwAQNg Now I've just asked Have there been any Foucault pendulum demonstrations in space?
– uhoh
May 9, 2019 at 1:18