EM Fields in LEO

[Classical Motion]

I have a question and someone here might know. Have they ever tried to magnetize and/or electrify and craft in low orbit? And if so could they detect any torque on it?

 

[billslugg]

Yes, magnetic torquers are used on Hubble to complement the reaction wheels. Hubble has no thrusters and torque wheels can max out on speed. Magnetic thrusters keep the torque wheels within RPM limits.

All spacecraft get electrified by high speed ions from the Solar wind. This is not desirable as it can occur differentially on various parts of the craft leading to discharges and damage. Many satellites have been lost due to this. Hard learning has lead them to encase the entire satellite in a conductive shield so that it is all at the same voltage. Any sparks go outward to space not between components.

The space tether is a conductive wire than can be used to extract energy from the Earth's magnetic field or it can be energized and used to raise a satellite's orbit.

Space tether - Wikipedia

 

[Classical Motion]

Is that in reference to braking the fly wheels? Am I following you? Not really familiar with Hubble's orientation methods.

I suspected that a tether would be charged. I was curious if any power could be harvested from it. I hadn't heard about an increase in altitude. That is interesting.

Someone ought to publish a chronological animation of the history of these electrical effects, and the methods of countering them....like on youtube or something. The only thing I have heard is about the re-entry plasma. Might be a good project for a student.

Have they tried other experiments, like attracting charge with E fields and M fields? Maybe we could get a recharge flying thru the aurora.

 

[billslugg]

Hubble has three flywheels, each for x, y and z axes. By speeding up or slowing down a wheel they can rotate Hubble around that axis. The problem is, if there are minute forces on the craft, eventually one of the wheels will get to its maximum operating speed. There is no way to slow it down without putting Hubble into a spin in the opposite direction. Normally they will use a thruster to push against the wheel so they can reduce its rpms. Hubble has no thrusters. It does have some loops of wire it can energize to push against Earth's magnetic field.
If you take energy from solar cells and inject it into a tether it can push against the Earth's magnetic field and raise the satellite.
If you pass the tether through the Earth's magnetic field and extract electicity from it you can drop the satellite down.
It is not desirable to allow a spacecraft to develop a net charge. It floats everything above ground and plays havoc with measurements. Many steps are taked to control charge and get rid of it. They don't need to use it to make electricity, they have plenty of that from the solar cells which basically recycle the same electrons over and over again.

 

[Classical Motion]

Thanks. Very interesting about the tether. I was thinking about the outer planets for the recharge. Where the sun is dim. But it would be hostile to pass thru electrically too. Maybe we could pass a recharging probe thru it, and catch it on the other side. And avoid dense particle areas.