T@P said:
i just went over this in physics, but if you take a coil, and pass a magnet near it (without touching), you create an emf while you come near it and when you leave. i believe its the Faraday effect/observation/whatever?
but with that in mind, i had this idea: if you take some really big coils and put them in space so the orbit the Earth say counterclockwise, and then take a big magnet and make it orbit the Earth clockwise, and some how hook it all up so that you when the current flows from the coils you say charge a really big battery or something. isn't that essentially free energy?
now i understand that most probably the satelite will fall because of the loss in energy, but if you position you coils just right, you could have it bounce sort of every time it passes through one, and maybe once every decade or so prop them up a bit? it sounds really insane but i just thought it might potentially work... any ideas?
I'm not sure what your point is. Is your intent to generate electrical energy using electromagnetic coils, or is your intent to find some use for the magnetic field?
If the second, it's more effective to reverse the process. Your electrical energy is essentially free (at least to you) since it comes from solar energy. Use your electricity to create a magnet. If you turn on your electromagnet, the magnet's magnetic field will try to align itself with the Earth, causing the satellite to rotate with the magnet.
If the Earth's magnetic field were aligned perfectly with the Earth's rotational axis (it isn't), you'd have a 'free' way to keep your satellite pointed at the Earth (provided your altitude is relatively low - the strength of the magnetic field tapers off pretty quickly). Considering you can't easily refuel a satellite, that would be a huge improvement over using thrusters to point your satellite. Unfortunately, the Earth's magnetic field isn't aligned with it's rotational axis.
Electromagnets can still be a huge asset on a satellite. Consider the fact that the atmophere doesn't abruptly end at some arbitrary boundary. Satellites below 1000km (around 600 miles) in altitude still encounter some atmosphere, even if very thin (above 1000km, the atmosphere is so thin that you could disregard it unless your satellite had an extremely high area to mass ratio - like Echo I, the first artifical communication satellite, which was basically a balloon with a reflective coating).
If you slap a humongous solar array on the side of your satellite, it's constantly being slowed by the atmosphere, causing your satellite to slew to one side (solar arrays also have a high area to mass ratio). You can compensate for that torque by spinning a wheel inside the satellite to create an opposite torque. Unfortunately, it's the change in wheel speed that compensates for the torque, not the actual wheel speed. Since the torque occurs constantly, your wheel has to accelerate forever. Your wheel can only spin so fast. Eventually you have to slow it down if you want to keep on using it to counter the torque from the solar array dragging through the atmosphere. You can fire a thruster to create an opposite torque, forcing your wheel to slow down (that's called a momentum dump), but you lose that capability once you run out of fuel.
Better is to use your electromagnet. If you turn on your electromagnet, the satellite will try to align itself with the Earth's magnetic field. This will put a torque on your satellite that you have to compensate for by changing the speed of your spinning wheel. If you turn your electromagnet on at the right time, the torque caused by the magnet trying to align itself with the Earth's magnetic field is opposite the torque caused by the solar array. In other words, the wheel slows down to compensate for the torque caused by the electromagnet and you don't have to use any fuel (polar orbiting weather satellites can last 5 years or more and may never fire their thrusters after they're stabilized in their orbit shortly after launch).
