Satellite compass

Satellite compass.

Ships. We no longer live in the Middle Ages, and modern ships are made of iron, not wood. However, any iron ship becomes magnetized. In the northern latitudes, the top of the iron structure will be attracted to the south magnetic pole, while the bottom will be attracted to the north. In the southern latitudes, it is the opposite. Only at the equator does this effect not occur. Therefore, a modern ship's magnetic compass is a very expensive device that requires complex calibration (while a satellite compass is cheaper).

Cars. Similar problems occur when using magnetic compasses in cars with a metal body. 

Drones. In drones made of plastic parts, where there are few magnetized components, cheap magnetometers are used, and they work well in forests and open areas. However, if you fly near reinforced concrete buildings or steel bridges, the magnetic compass will display incorrect data. Additionally, powerful drones have strong motors that create significant electromagnetic interference. In general, a magnetic compass is a device that shows approximately the correct course (sometimes incorrect). Furthermore, it indicates the course to the magnetic pole, not the geographic pole, so declination needs to be taken into account for correction.

Gyrocompasses. Gyrocompasses gradually lose their course. The speed at which they lose it depends on the temperature and the price of the model. Cheap gyrocompasses lose their course within seconds, expensive ones - within hours. The thing is, gyrocompasses work by integrating small rotations, so their error accumulates over time.
Another disadvantage of gyrocompasses is the problem with the initial course setup. The gyrocompass needs to remain still for a long time in order to determine the course based on the rotation of the Earth with at least minimal accuracy. Usually, the course is set externally (for example, airplanes deliberately travel along the center of the runway to align the gyroscopes with the course).

Laser and fiber-optic gyroscopes are very good solutions and offer the best accuracy. However, they are not compact and are very expensive.

Satellite compasses are also not the ideal solution. Why?

• Firstly, they require an open sky to receive satellite signals (they don't work under bridges or in tunnels).
• Secondly, their accuracy depends on size, meaning the distance between the antennas. The approximate course standard deviation is 0.25 degrees for an equilateral triangle with a one-meter side.
• Thirdly, a satellite compass provides one angle measurement per second with good accuracy. However, if there are 10 measurements, the accuracy will be three times lower.

On the plus side, the satellite compass does not have any problems with the initial setup, and there are practically no errors during operation. In other words, the integral of the solution error over a day is zero. And yes, it is relatively inexpensive.

Another advantage of the satellite compass is that it is not affected by multipath interference. If an obstacle reflecting signals is located at a distance ten times greater than the distance between the antennas, the compass adjusts to work considering this obstacle. Therefore, the satellite compass works fine on mountain slopes, near large buildings, and in modern urban areas (problems may arise only in ancient and medieval architecture).

Satellite-inertial compass is the ideal solution. It uses an inexpensive inertial gyroscope to smooth out the course, provides up to 100 solutions per second, and works under bridges, in tunnels, and other areas with poor reception.

© Eltehs SIA 2023