Magnetorquers (also known as magnetic torquers or torque rods) are used in small satellites to provide attitude control – maintaining the satellite’s orientation with respect to an inertial frame.
Magnetorquers produce a magnetic field around the satellite which interacts with the Earth’s own magnetic field, thus producing a torque on the satellite. 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.
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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.
The primary uses of magnetorquers
Magnetic torquers are routinely used in initial de-tumbling maneuvers – the process of stabilising the satellite’s angular momentum after orbital insertion. 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. These include:
- The torques that can be provided are very limited and only serve to accelerate or decelerate the change in a spacecraft’s attitude by minute amounts.
- It may be impossible to control attitude in all three axes, even when the full collection of three torquers are used, because the torque can be generated only perpendicular to the Earth’s magnetic field vector.
- Their dependency on the Earth’s magnetic field makes the use of magnetorquers difficult beyond the Low Earth Orbit (LEO).
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.
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The CubeTorquer portfolio by CubeSpace
CubeTorquers are nanosatellite magnetic torquers that contain a specially-treated ferrous core with ultra-low remanence and high linearity. They can be used for detumbling, coarse attitude changes and to desaturate reaction wheels.
The components are designed to be very compact through the use of a low-profile air-core coil that slots into the stack between the CubeSat PCBs. This enables a very compact 3-axis magnetic control system to be created in order to enhance satellite control.
The CubeTorquer product portfolio consists of:
CubeTorquer Small – a 28g torquer with magnetic moment of -0.24 A m^2 to 0.24 A m^2. The component is 18 x 62 x 14 mm and has magnetic gain of 2.8 A m^2 A^-1.
CubeTorquer Medium – a 36g torquer with magnetic moment of -0.66 A m^2 to 0.66 A m^2. The component is 18 x 77 x 14 mm and has magnetic gain of 8.2 A m^2 A^-1.
CubeTorquer Large – a 72g torquer with magnetic moment of -0.66 A m^2 to 0.66 A m^2. The component is 18 x 153 x 14 mm and has magnetic gain of 25 A m^2 A^-1.
CubeTorquer Coil – a 46g torquer with magnetic moment of -0.13 A m^2 to max: 0.13 A m^2. The component is 90 x 6 x96 mm and has magnetic gain of 2.1 A m^2 A^-1.
The NCTR-M012, NCTR-M002 and NMTR-X [Custom] by NewSpace Systems (Pty) Ltd.
NewSpace Systems’ magnetorquers use a magnetic alloy rod which produces an amplification effect over an air-cored magnetic torquer. 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.
Weighing just 7.5 grams and at only 3.2 millimeters thickness, the MT01 Compact Magnetorquer is a vacuum core magnetic coil designed for ADCS control. 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 0.2 Watts at a LEO orbit of 500kms.
The MT01 can be used with the EXA BA0x family of high capacity compact batteries and DSA Deployable Solar Array family. 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.
The AAC Clyde Space MTQ800 magnetorquer offers one of the highest energy efficiencies in the industry, combined with fine-grained dipole-moment strength control. Suitable for 50-200 kg class satellites, the system enables precise pointing and rapid de-saturation of any reaction wheel in the satellite.
The MTQ800 also features an innovative boost-mode that can pushes it to a higher magnetic dipole moment, for short duration manoeuvres, by sacrificing some energy efficiency.
The VMT-35 is a magnetic torquer designed specifically for small satellite attitude control. 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.
ZARM Technik AG has provided Magnetic Torquers for over 100 international missions. Since 1999 more than 200 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.
ZARM Technik AG’s qualification and acceptance testing ensures that there is virtually no potential for degradation either on the ground or in-orbit. The torquer’s most critical component – its core material – has been specially heat-treated to ensure optimum magnetic properties. Each unit is totally encapsulated, robust against mechanical and thermal loads and, except for the core, made with non-magnetic components.
The ISIS Magnetorquer Board (iMTQ) consists of a three-axis magnetorquer with three actuators, two torque rods and an air core. It is compatible with PC-104 mechanical interface and features I2C control for use in CubeSats. The iMTQ can provide magnetic attitude control and perform reaction wheel saturation and de-tumbling manoeuvres for CubeSats up to 24kg (12U).
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 0.67g.
Meisei Electric provides a complete range of magnetorquers, with products in every common satellite size; pico, nano, micro, small satellites and CubeSats. Meisei’s magnetic torquers feature an original design and an optimised balance of power consumption and mass.
This model is for 50 to 100 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.
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