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I've just read in Eshleman et al 1977 Radio Science Investigations with Voyager that the voyagers have:

...a novel attitude-control thruster configuration that minimizes accelerations along the Earth-spacecraft line-of-sight;

I am guessing that the goal would be to minimize any tiny amount of delta-v that would affect doppler measurements of velocity, since there is so much science available in these precision measurements.

Does this just mean that the "novel attitude-control thruster configuration" is designed to balance the impulse from the thrusters used so that only torque is applied about the spacecraft center of mass? If so, how was this novel minimization accomplished?

If it doesn't, then what does it mean?

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Per the Voyager Press Kit:

The 16 thrusters on the mission module each deliver 0.89 N (0.2-lb.) thrust. Four are used to execute trajectory correction maneuvers; the others in two redundant six-thruster branches, to stabilize the spacecraft on its three axes. Only one branch of attitude control thrusters is needed at any time.

I can only assume that means that each of them are in pairs. That being the case, I suspect that they are set up on opposite sides of the spacecraft, mass wise, such that when you rotate, you counteract any thrust that isn't a rotation. Essentially this means that the thrust must occur on opposite sides of the center of mass. The effect must be that there is no net force traveling through the center of mass.

If you apply only a single thruster, it will rotate the spacecraft, but also cause a small amount of movement. Multiple thrusters, and you can actually cause some movement. Imagine that you hit a car, say, at the passenger's side front wheel. The car will start to spin, but it will also move away from you. If you could hit both he passenger's side front wheel and the driver's side back wheel, assuming it was balanced, then the car would rotate, but not move. That is the idea with the updates to the Voyager system attitude adjustment.

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    $\begingroup$ So is your answer to Does this just mean that the "novel attitude-control thruster configuration" is designed to balance the impulse from the thrusters used so that only torque is applied about the spacecraft center of mass? therefore "yes"? I think you are trying to re-explain that sentence but with vaguer terms. Also could you explain more clearly, using proper engineering terminology what "opposite sides of the spacecraft, mass wise" actually means? How does one do that using math? $\endgroup$ – uhoh Jan 12 '18 at 1:05
  • $\begingroup$ The answer to the first question is yes. As for the second one, I'll try to improve the wording some. $\endgroup$ – PearsonArtPhoto Jan 12 '18 at 1:23

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