# The Naked Scientists Forum

### Author Topic: Which way will a magnet point in space?  (Read 235 times)

#### chris

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##### Which way will a magnet point in space?
« on: 06/10/2016 00:22:50 »
If an astronaut takes a magnet, or even a map-reading compass, into inter-planetary space, what, if anything, does the needle point to?

#### Colin2B

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##### Re: Which way will a magnet point in space?
« Reply #1 on: 06/10/2016 00:42:44 »
I assume along the field lines of the nearest planet or star with a magnetic field, or the strongest field.
If that were the case then an astronaught above one of the earth's poles would find it pointing down, but one above the equator would see it as being at a tangent to the earth's surface.
This assumes the nearby spaceship isn't magnetic!

I seem to remember a film where the astronaught wore magnetic boots to allow him (they were always him in those days) to walk on the outside of the spaceship. So in that case it would point down.

#### PmbPhy

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##### Re: Which way will a magnet point in space?
« Reply #2 on: 06/10/2016 05:09:02 »
Quote from: chris
If an astronaut takes a magnet, or even a map-reading compass, into inter-planetary space, what, if anything, does the needle point to?
There wouldn't be any direction which would be special since, for all practical purposes, the magnetic field in interplanetary space is zero. So it would be like asking which way a wooden needle would point if was in the same place. It would point in the direction determined only by the inertial properties of the needle.

#### evan_au

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##### Re: Which way will a magnet point in space?
« Reply #3 on: 06/10/2016 10:12:48 »
Quote
If an astronaut takes a magnet into space, what, if anything, does the needle point to?
Satellites in Low Earth Orbit often use a Magnetorquer to orient the satellite in space, by using Earth's magnetic field.

Small satellites can use a permanent magnet; larger satellites tend to use electromagnets.

This avoids the moving parts of momentum wheels (momentum wheel failure is what eventually disabled the Kepler extrasolar planet survey satellite).

The torque available from Earth's magnetic field is very small; an astronaut's normal body movements would exert a greater torque, so the magnet wouldn't help orient the astronaut (or his spaceship) at all. Manned missions tend to use small rocket thrusters.

When and if Earth's magnetic field decays to zero, changes to a quadrupole configuration or flips entirely, satellites using Magnetorquers could lose control of their orientation.

#### PmbPhy

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##### Re: Which way will a magnet point in space?
« Reply #4 on: 06/10/2016 13:47:03 »
Quote
If an astronaut takes a magnet into space, what, if anything, does the needle point to?
Satellites in Low Earth Orbit often use a Magnetorquer to orient the satellite in space, by using Earth's magnetic field.

Small satellites can use a permanent magnet; larger satellites tend to use electromagnets.

This avoids the moving parts of momentum wheels (momentum wheel failure is what eventually disabled the Kepler extrasolar planet survey satellite).

The torque available from Earth's magnetic field is very small; an astronaut's normal body movements would exert a greater torque, so the magnet wouldn't help orient the astronaut (or his spaceship) at all. Manned missions tend to use small rocket thrusters.

When and if Earth's magnetic field decays to zero, changes to a quadrupole configuration or flips entirely, satellites using Magnetorquers could lose control of their orientation.
It should be pointed out at this point that satellites in orbit of the Earth are not that far from the surface of the Earth since the radius of its orbit is almost the same as the radius of the surface of the Earth. Satellites in low Earth orbit are less than 200 km. That means that the strength of the magnetic field up there is approximately the same as it is on the Earth's surface.

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##### Re: Which way will a magnet point in space?
« Reply #4 on: 06/10/2016 13:47:03 »