Tks Tony for comment,
What I was trying to explain is that magnetic field is a dipole, with each pole pointing away of the magnet.
Rotation in the compass needle is caused by rejection of alike poles and attraction of different poles, and as such is producing a force. So the needle moves and in fact does receive energy otherwise it will not be moving.
I was not speaking on using an speaker magnet, we have a free magnet that is mother earth. This marvelous magnet is causing auroras as one demonstration of its energy. Why not use this magnet by opposing a magnet created at the satellite at the right earth spot where magnetic lines are pointing straight away from earth?.
It is amazing what recent CO Japanese Cubesats are doing with magnetorquers. They can keep a 1 degree Z plane accuracy pointing to earth !! . It is also amazing I can copy 80mw CW from these birds quite strong and readable, due their antennas are pointing right to earth. These sats have magnetometers able to resolve a small fraction of a Gauss in three planes, so they know where they are, and which direction is pointing the earth magnetic field.
So at the right point at the right satellite position these birds can send a controlled PWM pulse to one or more magnetorque coils with objective of producing a repelling force against earth magnetic field.
As satellite is at a stable height situation, then a small force can do things and perhaps raise her orbit. Their small keps decay possibly could be overcame thus keeping a healthy and longer life for the bird. This could be useful for satellites in orbit endangered by low orbit as those launched from the ISS.
Just dreaming on possibilities.
Thanks much for time and comments !
Best 73, Pedro Converso lu7abf@amsat.org.ar www.amsat.org.ar
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Tony Langdon wrote:
Subject: [amsat-bb] Re: Earths Magnetic Field strength From: Tony Langdon vk3jed@xxxxxxxxx Date: Thu, 22 Feb 2007 07:12:15 +1100 At 03:00 AM 2/22/2007, lu7abf wrote:
If the separation between poles of a small magnet defines strength of force, then a small separation as in a magnetic compass needle only 1 inch long placed at equator, over 6000 miles from poles will not move. Instead it does.
But that is rotation, which is equivalent to magnetotorquing, and we all agree this works well. However, your compass for a rare earth speaker magnet doesn't actually move across the table top in Earth's magnetic field, does it? THAT would be equivalent to trying to move the satellite into a new orbit.
73 de VK3JED http://vkradio.comIf the separation between poles of a small magnet defines strength of force, then a small separation as in a magnetic compass needle only 1 inch long placed at equator, over 6000 miles from poles will not move. Instead it does. Also much smaller magnetic dipoles even molecular inside a melted ferrous material does orient and keep their mood if material crystallize.
I think it is a matter of poles orientation i.e. on small needle, north pole is opposite to south, so it does not exert force in the same direction of the south pole, but opposite. (It's difficult to explain without using a sketch, and in a not my mother language, excuse me)
Regards to everybody and thanks for lending some brain cells to the idea of trying control bird's height.
73, Pedro Converso lu7abf@amsat.org.ar www.amsat.org.ar
Robert Bruninga wrote:
I moved a handheld compass towards a heavy... speaker magnet. When the compass was a few inches away from the magnet, it changed direction from North to the direction of the magnet.
As someone else pointed out earlier, that is because of the gradient or difference in "force" on one end versus the other. One end of the compass was an inch or so closer to one pole of the magnet than the other end.
But in space, the pole of your spacecraft magnet that you are trying to repel, is only one foot closer to the Earths pole, than the other pole which is attracted. So the difference in distance of the force that is pulling to the one that is pushing is only 1 foot out of say 21,120,000 feet to the Earth's pole. Hence the net force difference is a 21 millionth SQUARED or .00000000000004 of the force that you observed on the compass.
Or something like that. Bob