# Can objects be deorbited by a satellite using a magnetic field?

Can a magnetic field be made around a satellite for a split second to gain or loose momentum from another satellite or debris with a few passes with a near-miss trajectories on larger debris? Could a less precise method be used by keeping the magnetic field on while passing the object slinging it out of orbit?

• There are satellites that use magnetic fields to maintain attitude. Oct 9, 2018 at 6:39
• @MagicOctopusUrn can you send me the link on that so I can read on it?
– Muze
Oct 9, 2018 at 18:19
• Here is the link: can-earth-magnetic-field-be-used-for-attitude-determination-in-leo Oct 9, 2018 at 18:47
• Satellites are build with alloys of light metals, but not from heavy ferromagnetic steel. Therefore the force of the magnetic field will be very small if not zero.
– Uwe
Oct 10, 2018 at 7:58

A magnetic field is one way for one satellite to exert a force on another, changing the orbits of both. Since satellites are mostly made of aluminium, titanium and carbon fibre based composites, however, it is not a very efficient one, a powerful magnet would be needed to produce a small force.

Also, if the "predator" is in a similar orbit to the target, it won't tend to pull it out of orbit, and if it's in a very different orbit, they will only be in range of any feasible magnet for a few milliseconds, which won't do much.

So, while it's not against the laws of physics, it doesn't seem likely to be a good engineering solution.

• This is a really good answers. The period of peak force caused by fyby's last for tens of minutes to several hours, whereas two spacecraft 3 meters wide differing by 10% in velocity will "feel each other" for only tens of milliseconds at best, probably less.
– uhoh
Oct 9, 2018 at 12:19
• @uhoh how much force can be snapped magnetically in tens of milliseconds?
– Muze
Oct 9, 2018 at 18:01
• @Muze Impulse is force × time so if the forces were equal but the time was a million times smaller, then the impulse would be a million times smaller as well. The problem is a little complicated, and there are several variables, but there's no way I know of to increase the force by even a thousand (1,000 times gravity) much less a million, in order to compensate this. Planets are big, powerful magnets are small.
– uhoh
Oct 9, 2018 at 23:38

No, the range of a magnetic field is too short to be usable.

1. Magnetic field strength is proportional to 1/r3, so a magnetic field is only effective at very short distances (less than 10 meters), and quickly becomes way too effective when the debris is in range.
2. You can only attract other objects using a magnet, you can't repel them. So you have to be very careful, or the debris will ram your magnetic device at high speed.
3. Switching an electromagnet off quickly is difficult. Switching the magnet off causes a voltage spike in the circuit, the net effect is that the magnetic field takes a while to disappear. Not what you want when you're attracting debris at high speed.

The strongest magnets in commercial use today are in MRI scanners. These typically use superconducting magnets with a field strength in the region of 1 T. When you put a metal object in the same room as the MRI scanner, it will be attracted by the magnetic field, shoot across the room and be trapped in the center of the magnet. Outside the MRI room (say 5 meters away) the magnetic force is too small to be noticeable. That's how small the usable range of a magnet is.

If you use a superconducting magnet, switching it off is even slower as you have to dissipate the current gradually (preferably without boiling the coolant).

• That is the question what is too close and not close enough?
– Muze
Oct 9, 2018 at 18:39
• @Muze At what distance could you use a magnet to attract a bullet shot from a 9mm pistol 500 ft away? I think the point was that it's not feasible without rendezvousing the object to a close trajectory so your velocity vector could be slowly, over time, altered by the magnetism. His point is that the objects in question would likely be on a different trajectory and would be traveling much faster than the magnet, giving it very little time to apply the force which drops off exponentially with distance. Oct 9, 2018 at 18:57
• @MagicOctopusUrn depends on the magnet. What is the biggest electromagnet can we send to space and can enough solar sail power it?
– Muze
Oct 9, 2018 at 18:59
• No, my point was to you that we don't really have magnets powerful enough to deflect bullets in different directions from a stationary location. If we did, we'd already have military applications for that technology and you'd basically have a Gaussian force-field. I don't know of that being used in practice. Oct 9, 2018 at 19:02
• @MagicOctopusUrn but we do. They weigh to much and we are not talking about a bullet but 2 objects that can be tracked with laser guiding.
– Muze
Oct 9, 2018 at 19:05