Is it feasible to create a strong dynamic dipole inside a satellite so that it can be rotated on its axes and even possibly pushed in a direction due to the Earth's Normal Electric field. This might be a very slow process, but considering it requires only electric power and no propulsion, could this be a probable technique?
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1$\begingroup$ See en.wikipedia.org/wiki/Electrodynamic_tether $\endgroup$– PM 2RingSep 9, 2019 at 19:30
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2$\begingroup$ Yes, Magnetorquers are used on CubeSats for this purpose. Also, this may be better on the Space Exploration site... $\endgroup$– astrosnapperSep 9, 2019 at 19:40
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2$\begingroup$ I think the magnetic field would be more realistic. $\endgroup$– peterhSep 9, 2019 at 20:58
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2 Answers
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This is an interesting idea, and could potentially be useful for an ultra-low power application.
Conventional magnetorquers require a constant supply of electrical current running through resistive copper coils in order to produce a torque using Earth's magnetic field. Since the Earth's magnetic field has a lumpy, offset and tilted dipole shape you need to know where you are with respect to the field in order to constantly recalculate the required current in your three axis coils in order to optimize your attitude control. (If you are only doing momentum unloading, you can be less precise)
If you can afford the electrical current to run the coils, then it's fine. But if you wanted a very low power attitude control system, an electrostatic charge distribution can be established with only a tranisent in current, plus a low level maintenance current to offset leakage as well as charging effects from charged particles trapped in Earth's magnetic field.
Your spacecraft's electrostatic field would then produce a torque depending on the orientation with respect to Earth's electrostatic field.
However, I am not sure if in a space environment the Earth's electrostatic field is as well behaved as you think it might be. It's probably going to be constantly messed up by space weather.
For an alternative low-power source of torque, I'd recommend you use an articulated permanent magnet. Have a small but powerful rare-earth permanent magnet on a 2-axis gimbal, and use very low power motors to move it around so that you generate magnetic torque without having to dissipate power in copper coils. For more on that, see Could an articulated permanent magnet work as a low-power cubesat magnetotorquer? Problems?.
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1$\begingroup$ As noted by astrosnapper in a comment to the question (back in the astronomy community?), magnetorquers have been used on CubeSats. I've been told they are used to detumble a CubeSat over a couple of orbits. But for actual orientation after that, reaction wheels are generally employed. $\endgroup$ Sep 12, 2019 at 1:09
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1$\begingroup$ @Rick0xfff Generally yes, but I can imagine the possibility of wanting to desing a budget cubesat that only has magnetotorquers for budgetary or mass or simplicity of design considerations; so I've just asked Are there any modern cubesats or smallsats that have relied only on magnetotorquers for attitude control? $\endgroup$– uhohSep 12, 2019 at 2:25
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$\begingroup$ What about spacecrafts orbiting near really powerful magnetic fields at periapsis, like Parker Solar Probe and Juno, could probes in such orbits enjoy delta-V bonuses comparable to what Cassini enjoyed from Titan's gravity? $\endgroup$ Sep 18, 2019 at 11:29
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Simply yes, and this has actually been used.
The most common suggestion is to use an electrical tether, basically just a length of cable played out on both sides of the satellite like two long antennas. Since the magnetic field is diminishing as you move away from the Earth, there is a potential difference across the tether.
If you drive an electrical current into the tether, from solar panels for instance, this will produce a force against the surrounding electric field, and the differences in the field cause that force to be asymmetric. This can be used to provide momentum exchange in a manner similar to an electric motor. This is known as tether propulsion. It can be used for orbital corrections and maneuvers.
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$\begingroup$ hmm... the question is about the electric field of the Earth, whereas what you are describing uses the magnetic field of the Earth, doesn't it? So the Earth's electric field has not been used yet, has it? $\endgroup$– uhohSep 18, 2019 at 13:45
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$\begingroup$ The two are one and the same. The magnetic field captures charged particles. Those particles form the electric field. We call this "electromagnetism" for a reason, the two are rarely separate things. $\endgroup$ Sep 19, 2019 at 13:44
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-1yes electric and magnetic fields are linked, but that doesn't mean they are the same thing or can be used interchangeably in a sentence. $\endgroup$– uhohSep 19, 2019 at 13:48 -
$\begingroup$ Statement editied. Further concerns? $\endgroup$ Sep 19, 2019 at 13:51
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$\begingroup$ No, continuation of the same concerns. The Electrodynamic tether uses the interaction between a current in the tether moving through the Earth's magnetic field. I am not sure if Earth has an appreciable electric field at orbital altitude, but you are going to have to explain in more detail the force you are talking about; right now I don't know of any force between a current and an electric field. If you can't add some specific supporting links or some math, your answer has the appearance of just making things up. $\endgroup$– uhohSep 19, 2019 at 15:33