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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A magnetorquer designed for 50-200 kg satellites, with a mass of 489 and power rating of < 13.2 W. The TRL 9 system has RS422 and I2C data interfaces and offers fine-grained dipole-moment strength control.
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The CubeSpace CubeCoil is designed for satellite applications. CubeCoil can be used for detumbling, coarse attitude changes, and desaturation of reaction wheels. It is a low-profile, flat-air coil and is intended to fit within a PC104 stack between PCBs. The product is available in ‘n single or double-wound versions that are suitable for 3U and 6U CubeSats respectively.
The CubeSpace CubeTorquer CR0002 is a nanosatellite magnetic torquer that uses a specially treated ferrous core with ultra-low remanence and high linearity. An extensive range of magnetic torquer rods is easy to integrate into satellite structures through the low-profile connector and different mounting options. With their compact design and low-profile connector, they are perfectly suited for satellites where space and mass are of high priority.
The CubeSpace CubeTorquer CR0003 is a nanosatellite magnetic torquer that uses a specially treated ferrous core with ultra-low remanence and high linearity. An extensive range of magnetic torquer rods is easy to integrate into satellite structures through the low-profile connector and different mounting options. With their compact design and low-profile connector, they are perfectly suited for satellites where space and mass are of high priority.
The CubeSpace CubeTorquer CR0004 is a nanosatellite magnetic torquer that uses a specially treated ferrous core with ultra-low remanence and high linearity. An extensive range of magnetic torquer rods is easy to integrate into satellite structures through the low-profile connector and different mounting options. With their compact design and low-profile connector, they are perfectly suited for satellites where space and mass are of high priority.
The CubeSpace CubeTorquer CR0006 is a nanosatellite magnetic torquer that uses a specially treated ferrous core with ultra-low remanence and high linearity. An extensive range of magnetic torquer rods is easy to integrate into satellite structures through the low-profile connector and different mounting options. With their compact design and low-profile connector, they are perfectly suited for satellites where space and mass are of high priority.
The CubeSpace CubeTorquer CR0008 is a nanosatellite magnetic torquer that uses a specially treated ferrous core with ultra-low remanence and high linearity. An extensive range of magnetic torquer rods is easy to integrate into satellite structures through the low-profile connector and different mounting options. With their compact design and low-profile connector, they are perfectly suited for satellites where space and mass are of high priority.
The CubeSpace CubeTorquer CR0010 is a nanosatellite magnetic torquer that uses a specially treated ferrous core with ultra-low remanence and high linearity. An extensive range of magnetic torquer rods is easy to integrate into satellite structures through the low-profile connector and different mounting options. With their compact design and low-profile connector, they are perfectly suited for satellites where space and mass are of high priority.
The CubeSpace CubeTorquer CR0012 is a nanosatellite magnetic torquer that uses a specially treated ferrous core with ultra-low remanence and high linearity. An extensive range of magnetic torquer rods is easy to integrate into satellite structures through the low-profile connector and different mounting options. With their compact design and low-profile connector, they are perfectly suited for satellites where space and mass are of high priority.
The CubeSpace CubeTorquer CR0020 is a nanosatellite magnetic torquer that uses a specially treated ferrous core with ultra-low remanence and high linearity. An extensive range of magnetic torquer rods is easy to integrate into satellite structures through the low-profile connector and different mounting options. With their compact design and low-profile connector, they are perfectly suited for satellites where space and mass are of high priority.
Magnetorquers rods are a method of controlling the attitude of a spacecraft either directly, by interacting with the local Earth's magnetic field or, more usually, in combination with reaction wheels. This secondary method allows for the dumping of excess momentum in the reaction wheels without the need for a complex propulsion system.
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