Orbital compass

I noticed a scene last week on Enterprise where the captain gave a
gift ship's compass to the first officer.

Question: given a non-ferrous place on the ISS, would a compass point
toward the North Magnetic Pole? Has this experiment ever been tried on
ISS, or are there just too many magnetic fields on-board?

I guess compasses don't work on ships like those of star trek (not even the
most advanced technique will ever be able to get rid of every field).
Compasses wouldn't work in general, but that all depends on where (and how)
you are in space.

"TVDad Jim" schreef in bericht
om...
I noticed a scene last week on Enterprise where the captain gave a
gift ship's compass to the first officer.

Question: given a non-ferrous place on the ISS, would a compass point
toward the North Magnetic Pole? Has this experiment ever been tried on
ISS, or are there just too many magnetic fields on-board?

TVDad Jim wrote:

Question: given a non-ferrous place on the ISS, would a compass point
toward the North Magnetic Pole?

No. A compass in general doesn't point toward the magnetic north pole, it
aligns itself, so that it is parallel to the field lines of the local
magnetic field.* Given a place in space with no disturbing magnetic fields
in the vicinity, this should work in space.

Has this experiment ever been tried on
ISS, or are there just too many magnetic fields on-board?

Hm, I doubt it. There wouldn't be much reason to do it. But a lot of
satellites have mapped Earth's magnetic field from orbit, e.g. the very
succesful Danish satellite, Oersted.

/steen

* Actually, a compass on Earth generally points toward the Earth's magnetic
/south/ pole, which is located in northern Canada. That's why the north pole
of a compass points north :-)

"Marco van Woerden"

Compasses wouldn't work in general,

because.....

but that all depends on where (and how)
you are in space.

For example......

TVDad Jim wrote:
I noticed a scene last week on Enterprise where the captain gave a
gift ship's compass to the first officer.

Question: given a non-ferrous place on the ISS, would a compass point
toward the North Magnetic Pole? Has this experiment ever been tried
on
ISS, or are there just too many magnetic fields on-board?

To be precise, an orbital magnet would indeed tend to align itself
with the planetary field as it traveled along. It also, of course,
responds similarly to *all* the various fields in which it's immersed.
(May the locally strongest field win!) Magnetometers have been carried
on satellites for many years to map the field, and they do it exactly
in this way, but they're also placed on long, inert booms to get them
far away from the rest of the spacecraft. If you get the instrument far
enough away from all the other hardware, the various small magnetic
fields become weak, and also can tend to cancel each other if the
engineers have been clever enough to orient all the sources just so.

This is true of the Pioneers 10 & 11 interplanetary probes, and
their close relatives, the Voyagers 1 & 2. These spacecraft carry their
magnetometers way out on the ends of long poles. But they also still
have some small contamination by their own, small magnetic fields. So
occasionally they'll do a calibration run, in which, as they slowly
rotate, they map their own fields. This is then subtracted from the
overall data on the ambient field in deep space.

Less rigorously, astronauts have also played with small dimestore
magnets while on orbit. If you impart a small rotation to the free
falling magnet, given enough time it actually loses its rotational
energy to Earth's field and settles into continuous alignment with the
changing field.

-Mark Martin

In article ,
TVDad Jim wrote:
Question: given a non-ferrous place on the ISS, would a compass point
toward the North Magnetic Pole?

Well, kind of -- it would do that if it were constrained to rotate only
horizontally. As others have explained, a compass needle tries to line
itself up with the local magnetic field, whose horizontal component points
to the N.M.P. But the field is generally not horizontal; this matters
even on aircraft, where you have to remember that if you're banking for a
turn, the compass will be lying to you somewhat.

Three-axis magnetometers -- which give a full 3D determination of the
field direction -- are routinely used for attitude sensing on LEO
spacecraft, and given a few orbits worth of data and a good magnetic-field
model, they can also be used for orbit determination.

Has this experiment ever been tried on
ISS, or are there just too many magnetic fields on-board?

I would guess that ISS is too magnetically "dirty" for a compass to work
very well, unless perhaps you found just the right place for it. Building
magnetically-clean spacecraft is somewhat of an art, and it imposes some
significant constraints, so it's not done unless there is real need.
(Even MOST puts its magnetometers out on short booms to get them away from
the rest of the spacecraft -- not the electronics, interestingly enough,
but the Invar components in the athermal telescope structure.)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In article ,
Steen wrote:
* Actually, a compass on Earth generally points toward the Earth's magnetic
/south/ pole, which is located in northern Canada. That's why the north pole
of a compass points north :-)

Yes and no and kind of. There are two separate uses of "north" and "south"
here, and it's important not to confuse them.

What's normally spoken of as the North Magnetic Pole is the magnetic pole
that is in the Northern Hemisphere. Confusingly, this is a *south* pole
by the polarity standard normally used for magnets, but that doesn't mean
that it's referred to as such when discussing geography.

A further complication is that because Earth's magnetic center is not at
its geometric center, the places where a three-axis magnetometer reports
that the field is vertical -- which are the places usually reported as the
magnetic poles -- are *not* in fact the places where the axis of Earth's
magnetic dipole intersects the surface.

To say nothing of the fact that the field is not an exact dipole... and
is changing with time in poorly-understood ways.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Henry Spencer wrote:

Well, kind of -- it would do that if it were constrained to rotate only
horizontally. As others have explained, a compass needle tries to line
itself up with the local magnetic field, whose horizontal component points
to the N.M.P. But the field is generally not horizontal; this matters
even on aircraft, where you have to remember that if you're banking for a
turn, the compass will be lying to you somewhat.

Three-axis magnetometers -- which give a full 3D determination of the
field direction -- are routinely used for attitude sensing on LEO
spacecraft, and given a few orbits worth of data and a good magnetic-field
model, they can also be used for orbit determination.


Geologists also use a multiaxis, or "dip" compass to determine the local
magnetic fields of rock strata.

Pat

"Henry Spencer" wrote in message
...

To say nothing of the fact that the field is not an exact dipole... and
is changing with time in poorly-understood ways.

And apparently changing more rapidly lately.


--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Henry Spencer wrote:

Yes and no and kind of. There are two separate uses of "north" and
"south" here, and it's important not to confuse them.

What's normally spoken of as the North Magnetic Pole is the magnetic
pole that is in the Northern Hemisphere. Confusingly, this is a
*south* pole by the polarity standard normally used for magnets, but
that doesn't mean that it's referred to as such when discussing
geography.

I stand corrected.

/steen