Nanosatellites are rapidly growing in popularity because of their cheaper manufacturing and launch costs. One of the dominant tools of nanosatellite attitude control are magnetorquers, they can be used as a sole attitude control device or in combination with other solutions to improve accuracy. Magnetorquers consist of three coils aligned perpendicularly to the directions of the three axes. Magnetorquers create magnetic dipole moment that interacts with earth’s magnetic field creating useful torque on the device. Because of this attitude control can only be achieved on two axes, that are perpendicular to earth’s magnetic field lines. Magnetorquers produce very weak torque $10^{-6}$ Nm, torsion balance, that was first developed by Colomb can be used to precisely measure very weak torques. The purpose of this paper is to design, manufacture and test torsion balance that can be used to measure torque of magnetorquers. In torsion balance, based on Hooke’s law, torque is measured by measuring angle by which the sample turns. To do this, stiffness of the fiber needs to be measured, this can be done by measuring resonant oscillation period of a sample with a known moment of inertia. It is important to select a sample of similar mass to the test subject, since as shown in this paper fiber stiffness depends on the tension of the fiber. Torque of magnetorquer depends on the angle between the earth’s magnetic lines and its magnetic moment vector. Maximum torque will be exerted when the coil’s magnetic moment vector is perpendicular to the earth’s magnetic lines, because of this, measured angle will not be linearly proportional to the maximum torque of the magnetorquer, so to avoid larger errors the fiber of the balance should be chosen so that the angle by which the magnetorquer turns would be small. Torsion balance was constructed mainly of aluminum because of its low magnetic permeability, adequate strength and wide availability. To align magnetorquer magnetic moment vector perpendicularly to earth’s magnetic field lines balance suspension head needs to be rotated, for this a stepper motor is used. The angle of rotation is measured using a camera by capturing the position of a dot projected on the screen by the laser beam reflected from the mirror suspended under the fiber. Maximum angle change of the test subject that can be measured by the torsion balance is 10°. To make measurements quicker its beneficial to use oscillation damper. A liquid damper with a rotating hexagon submerged in liquid is a simple and effective solution. It was empirically found that the best liquid for the damper is starch paste (1 l of water to 6 g of starch). This torsion balance was used to successfully measure the torque of a magnetorquer integrated into a solar panel, capable of 0,93 $\mu Nm$ maximum torque at the test location.


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    Titel :

    Sukamosios svarstyklės mikroniutonmetrų eilės sukimo momento matavimui ; Torsion balance for torque measurement in micronewton metre scale



    Erscheinungsdatum :

    2017-06-06


    Medientyp :

    Hochschulschrift


    Format :

    Elektronische Ressource


    Sprache :

    Lithuanian , Englisch


    Klassifikation :

    DDC:    629