Designing a spherical motor that actually works has vexed the ambitions of many scientists and engineers, but a Taiwan startup has developed a tiny satellite altitude control system using spherical motor technology that it believes can help more commercial players enter the space industry. Tensor Tech of Taipei showcased its novel system at CES 2020, held virtually in January.
A spherical motor can spin and provide angular momentum in X, Y, and Z axes. The rotor is supported with a gimbal mechanism and bearings, and a 3D rotating magnetic field is the driving force instead of a 2D rotating magnetic field that powers conventional motors. Controlled by a patented, magnetic field design, the Tensor Tech motor can replace three separate motors in a cubesat.
Moreover, bias-currents are applied to each phase of the motor, enabling it to combine 3-axis magnetorquers into the device as well. A magnetorquer is a satellite system for attitude control, detumbling, and stabilization built from electromagnetic coils. The magnetorquer creates a magnetic dipole that interfaces with Earth’s magnetic field.
“There are two obstacles for commercial players to enter the space industry: rocket launching costs and satellite building costs,” says Thomas Yen, co-founder and CEO. “To tackle these problems, satellite miniaturization is the key. Yet the attitude control system (ACS) tends to be the heaviest and largest of all the related subsystems.
“For decades, the size of the ACS could not be reduced significantly due to physical limitations. Tensor Tech has developed groundbreaking spherical motor technology that replaces three motors with just one. Our device’s weight, size, and power consumption are two-thirds that of traditional systems,” he explains.
Every satellite in orbit requires precise orientation control along the X, Y, and Z axes. This so-called attitude control is essential for optical-sensing and broadband communication satellites. To achieve this, Tensor Tech uses a tactical-grade gyroscope and fine sun sensor as the attitude determination sub-system, while the spherical motor functions as the attitude actuator.
The company gives the following description of its system. The Satellite Attitude Determination and Control System is designed for CubeSats of 1.5U, 2U, 3U, and 6U. A full set of attitude determination-actuator hardware and firmware is embedded. This sub-system combines six fine sun sensors, a reaction sphere and a tactical grade gyroscope to provide pointing accuracy. /One reaction sphere can perform the same function as three traditional reaction wheels, but at nearly one-third of the volume, cost, weight, and power consumption. In terms of rotational dynamics, the motor functions like a single-gimbal control moment gyro but is actuated by the spherical motor. For more info, see www.tensortech.com.tw.