# Tag Info

22

Earth's magnetic field is way too weak to repel against with the force required to launch anything into orbit. Actually, it's really easy to demonstrate that. Take one fridge magnet, place it on the kitchen scale, and write down its weight. Then turn the magnet around and weigh it also with its polarity reversed. You shouldn't see any difference and the ...

15

A set of three orthogonally aligned torque rods wired up so they can generate a magnetic dipole field of either sign (i.e. flip the North and South poles) can generate a magnetic field of arbitrary orientation (up to the maximum vector sum of the dipole moment of each rod individually). This artificial field interacts with the Earth's magnetic field to ...

13

Given the question, as written (rather than the misleading title) - yes, a magnetic accelerator could be used to launch a spacecraft. The issues with so doing are several. the contents of the craft need to survive the magnetic fields needed for reasonable length accelerators the track the linear track is extremely long the circular track causes fairly ...

10

RAX and RAX-2 and possibly other cubesats launched by the University of Michigan (I can't remember at the moment) used fixed neodymium based magnets on their Z+ axis. Hysteresis was added to dump any residual momentum after P-Pod ejection. On the RAX missions, the magnets then were used to orient the satellite vertically over the poles where the science ...

6

If they were going to be used anywhere else, it would have to be with one of the Gas Giants, because no other planet has enough magnetic field in the solar system to use them. Furthermore, it would be an orbiter of some kind, because it wouldn't make sense to use them for only the short period of time when flying by the planet of interest. Thus, the ...

6

No, a magnetorquer would be useless in orbit around Mars. Mars has a surface field strength of maybe a few tens of nanoteslas. That's less of a magnetic field strength than a cassette tape. To make things worse, there isn't one single magnetic field, but a collection of weak remnant fields. Mars used to have a global magnetic field a few billion years ago, ...

4

To answer this portion of the question: Isn't magnetic force technically stronger than gravity?? The magnetic force is stronger than gravity, but only at close range. Magnetic field strength is proportional to $1/r^3$, where r is the distance to the magnet. Earth's gravity is proportional to $1/r^2$, where r is the distance to the center of the earth. ...

4

Basically, most magnetorquers function something like bar magnets that can be dialed to select how powerful, and what direction, they pull in. The math behind them turns out to be really simple. $\mathbf{\tau}=\mathbf{\mu}\times\mathbf{B}$, where $\tau$ is the torque on the satellite, $\mathbf{B}$ is the ambient magnetic field, and $\mu$ is the magnetic ...

4

I can't give a definitive answer until I have numbers on how much torque that the devices can output, which I wasn't able to find on the Interwebs. However, Wikipedia paints a grim picture for the possiblity of their use on larger sattelites: Disadvantages The main disadvantage of magnetorquers is that very high magnetic flux densities would be needed if ...

3

The cases you've mentioned are applied to three-axis attitude control systems. In the past (and oddly even today), magnetic torquers were used to replenish the angular momentum of spin-stabilized spacecraft. The simplest example that comes to mind is SCD 1 and 2: The ACS is responsible to stabilize and control the spacecraft orientation with respect to ...

3

The existing answers pretty much show why it's not done but I'll add a couple more points also: 1) Remember that a rocket going up these days pulls several Gs. Note how far it goes before the engines shut down--hundreds of miles. If you want the same G load you need as much distance--for humans to survive the trip your launcher needs to be hundreds of ...

3

How do we manage the residual magnetic moment of magnetorquer with a ferromagnetic core? I can recommend two methods. Either might work alone, and they could also be used in combination. There may be others in practice as well. 1. Degauss the rod carefully after each torquing session From Wikipedia's Degaussing; Magnetic data storage media: Erasure via ...

3

Understanding how to test and qualify systems of a satellite prototype is certainly on-topic in Space Exploration Stackexchange. Cubesat development is always conceptual at first, and you definitely need to use some physics to develop your understanding. That doesn't mean the question should be moved to Physics Stackexchange. Measure in the plane ...

2

If a reaction wheel is spinning at maximum speed and you turn off the motor it will slowly decelerate because of friction. Potentially, depending on how it's designed, it might regeneratively brake as well, which will convert the stored momentum back into electricity. Because of the conservation of angular momentum, as the wheel slows down, the satellite ...

2

This is an excellent question, and in fact one that plagues many small satellite designs! There are a number of means that are typically done to adjust for the effect of a magnetorquer/ magnetometer reading issues. Don't use the magnetometer while the magnetorquer is being used. If you don't require a 100% duty cycle of the magnetorquers, this can be the ...

2

Okay, so I've asked around and I received an answer: Yes, $K$ has no general formula. I do not have the exact steps, but it goes as follow: the local demagnetizing factor must be integrated with respect to the volume. This factor depends on the position of each element of the core reported to the winding, therefore there is no simple analytical answer. For ...

2

M-Cubed is (was?) a cubesat build at the University of Michigan that sort-of qualifies: The satellite uses a small permanent magnet and orthogonal mu-metal dampening strips as passive attitude control to slowly orient its Z axis to the Earth's polar magnetic field lines. (It carries no other orienting hardware) Why just "sort-of"? The Michigan ...

1

The ELFIN cubesats use magnetotorquers for attitude control.

1

See this paper for a good description of how to measure magnetic dipoles. To summarize, the approach is to use a calibrated magnetometer at a fixed distance from the torque rod and back out the dipole from the measured magnetic field. The test should be conducted with as little ferrous material in the test environment as possible. Obviously, the background ...

1

No. No object can exert a torque on itself via only internal interactions. That would violate conservation of angular momentum. Spacecraft are constructed to have controlled, usually zero, magnetic fields to reduce torque from external fields they encounter.

1

Yes, there is absolutely torques generated on the spacecraft from a combination of residual spacecraft magnetic field (static, produced by magnetic or paramagnetic materials in the construction) and dynamic resulting from the flow of electrical current around the spacecraft. There will be some interaction of these magnetic fields with the magnetic field of ...

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