Go Back Torque on a Current Loop The torque on a current-carrying coil, as in a DC motor , can be related to the characteristics of the coil by the " magnetic moment " or "magnetic dipole moment". The torque exerted by the magnetic force including both sides of the coil is given by The coil characteristics can be grouped as called the magnetic moment of the loop, and the torque written as The direction of the magnetic moment is perpendicular to the current loop in the right-hand-rule direction, the direction of the normal to the loop in the illustration. Considering torque as a vector quantity , this can be written as the vector product Since this torque acts perpendicular to the magnetic moment, then it can cause the magnetic moment to precess around the magnetic field at a characteristic frequency called the Larmor frequency. If you exerted the necessary torque to overcome the magnetic torque and rotate the loop from angle zero to degrees, you would do an amount of rotational work given by the integral The position where the magnetic moment is opposite to the magnetic field is said to have a higher magnetic potential energy.
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In this manner the angular momentum of the satellite can be changed and controlled. In this article we discuss how magnetorquers work, the tasks they perform, the advantages and disadvantages of using them, and give an overview of some of the products currently available on the global marketplace for space.
If you would like to skip the introductory material and go straight to to view the available products, please click here , otherwise please read on. Note that these products are just some examples of the magnetorquers available on the market today - we are actively updating the post with new models and suppliers. Magnetorquers have low power consumption, which matches the very low power availability during the initial orbital phases, after the satellite is injected into the orbit by a launch vehicle.
Magnetorquers are also used as a part of a three-axis control system when low power and little physical volume is available on-board the spacecraft. They can be stably mounted on surfaces of the satellite body and if three magnetorquers are mounted to three orthogonal surfaces then they can provide three-axis stabilisation.
They can also be used to unload the momentum of complementary control actuators such as reaction wheels. Magnetorquer performance characteristics Where satellites are concerned, the required control torque is determined by control law. This torque is generated by passing the electric current, determined by the control law, through the torquer.
Considering the structural and material aspects of magnetorquers, the following main factors affect its performance: The material of the coil: this can be made from either copper or aluminium. Aluminium wires are lighter in weight whereas copper wires have lower resistance. The material of the core: typical magnetorquer cores are usually filled with air or made from ferromagnetic material.
High permeability is favourable and the material should have large linear region. Length, cross-sectional area of coil and rod: these physical parameters should be chosen such that they obey the relevant power and mass constraints. Time constant: this should be a reasonable value in order for steady state to be achieved quickly.
The advantages of using a magnetic torquer There are a number of distinct advantages that using a magnetorquer provides over alternative control systems: Unlike other active actuators that need consumable materials, such as thrusters , they can in theory work indefinitely as long as sufficient power is available to match the resistive load of the coils.
The absence of moving parts makes them significantly more reliable than using momentum wheels and control moment gyroscopes. Magnetorquers consume little power and occupy less volume than alternative control systems.
The disadvantages of using magnetorquers alone Despite their unique benefits there are some disadvantages to using magnetorquers alone to manipulate and control satellite attitude. In spite of these issues, magnetorquers remain one of the most successful and popular attitude control system options and we regularly receive requests for information on available products.
Magnetorquers available on the global market In the article section below we have included a selection of the magnetorquer products currently available on the market. Please note that this list will be updated when new products are added to the global marketplace for space - so please check back for more or sign up for our mailing list at the link below for updates. A specialised heat-treated magnetic alloy is used in CubeRod cores, and all rods are handled by trained personnel to avoid any shocks which could degrade their performance.
This high-quality manufacturing process, combined with the use of premium materials, enables the CubeRod to provide best-in-class performance. Three standard size rods are available along with customised torquers for satellites with requirements not met by the standard offerings.
They allow precise pointing and rapid de-saturation of any reaction wheels in the satellite. The magnetorquers feature a unique boost-mode that pushes them up to a higher magnetic dipole moment for short duration manoeuvres by sacrificing some energy efficiency. In return the magnetorquers can offer the fastest de-tumbling of any satellite in this mass class, allowing users to start their operations in the shortest amount of time. They also feature an inherently safe, passive de-tumbling mode which works without any external controller.
This construction uses little power and is less susceptible to magnetic torque variations caused by temperature fluctuations. Each rod is typically bifilar-wound for redundancy, or the windings can be activated together to increase the torque produced.
While drive circuits for the rods can be supplied if required, they typically run directly between a switched power output and the on-board power control system. The magnetorquers have a simple interface, feature a high moment for low power, small size and low mass, very little residual magnetic moment and are adaptable for size, moment and power to meet optimal system requirements.
It consists of a core, made of magnetically soft material with a high permeability, with a coil of copper wire wound around it. The coil and core are located in a black, anodized aluminium tube and encapsulated in resin to ensure isolation. The coil has a direct connection to the connector so that current, and thus the magnetic field, can be directly controlled. Parameters such as the geometry, number of windings, wire diameter or ohmic resistance of the torquer can be customised as needed.
Since more than units have been developed, with zero failures during operations and tests - for example, the Magnetic Torquers on board the GRACE satellites were operational for more than 10 years. Each unit is totally encapsulated, robust against mechanical and thermal loads and, except for the core, made with non-magnetic components.
The iMTQ can provide magnetic attitude control and perform reaction wheel saturation and de-tumbling manoeuvres for CubeSats up to 24kg 12U. Suitable for 1U to 3U CubeSats it boasts an impressive level of performance with low mass, power requirements and physical volume. The MT01 is capable of greater magnetic moments, turn speeds and angular accelerations than many comparable products on the market; for example, it can turn a 1U mass 90 degrees in 60 seconds using only 0.
In addition, the biggest advantage of the MT01 is that it can be easily affixed anywhere on a spacecraft using a minimal area.
Every coil is tested and qualified and then shipped with full reports, as well as being packed with additional match connectors interfaces. Magnetic Torquer by Chang Guang Satellite The magnetic torquer creates a magnetic moment to control the satellite attitude by interfacing with the magnetic field of the earth.
Internally the product uses soft magnetic materials and enamelled, high-reliability copper wires, while on the exterior high-rigidity carbon fibres are used. The Chang Guang Satellite magnetorquer has been applied and verified to many of the in-orbit satellites of Jilin-1 series. It operates at a voltage of 12V, has power requirements less than 3W and weighs just 0. Magnetic Torque Actuators by Meisei Electric Meisei Electric provides a complete range of magnetorquers, with products in every common satellite size; pico, nano, micro, small satellites and CubeSats.
This model is for 50 to kg satellite and is flight-proven and ITAR-free. The system is fully customisable in terms of the magnetic moment, dimensions, mechanical and electrical interface. Meisei Electric is also able to provide advanced magnetorquer systems at low costs due to the use of commercial off-the-shelf COTS parts. Technology The O.
The magnetic bar is an Ni36Fe64 alloy which has a low coercive force and a high saturation magnetic induction intensity.
This enables the magnetorquer to keep only a small residual magnetic torque level, maintaining the linear relationship between magnetic torque and coil current. The MQ is a Am2 magnetic bar that has been used in more than 10 missions. It has an operating voltage of 40V and a power consumption level of less than 4.
The MQ10 features a 10 Am2 magnetic bar and an operating voltage of just 10V. It also has a power consumption of less than 0. Thanks for reading! Subscribe to get our weekly newsletter on the latest trends in the space industry I would like to receive the weekly satsearch newsletter, which may include sponsored and promoted content, as well as occasional updates and news about satsearch.
Construction[ edit ] The construction of a magnetorquer is based on the realization of a coil with a defined area and number of turns according to the required performances. However, there are different ways to obtain the coil; thus, depending on the construction strategy, it is possible to find three types of magnetorquer, apparently very different from each other but based on the same concept  : Air-core magnetorquer: this comprises the basic concept of magnetorquer, a conductive wire wrapped around a non-conductive support anchored to the satellite. This kind of magnetorquer can provide a consistent magnetic dipole with an acceptable mass and encumbrance. Embedded coil: this kind of magnetorquer is constructed creating a spiral trace inside the PCBs of solar panels which generates the effect of the coil. This solution is the one with the least impact on the satellite as it is entirely contained within the solar panels. However, due to the physical limit in the board thickness and the presence of other circuits and electronic components, it is not possible to reach a high value of the magnetic dipole. Torquerod: this kind of magnetorquer is the most efficient solution.
Magnetic Torquer for Small Satellites
ISIS Magnetorquer board