Cubesat Attitude Control Utilizing Low-Power Magnetic Torquers & A Magnetometer

Abstract

The CubeSat Project has lowered development time and costs associated with university satellite missions that conform to their 10 centimeter cube design specification. Providing attitude control to a spacecraft, of such small volume, with a very limited power budget has been a challenge around the world. This work describes the development of an attitude control system based on a very low-power magnetic torquer used in conjunction with a magnetometer. This will be the first flight use of this torquer which is composed of a hard magnetic material wrapped inside of a solenoid. By discharging a capacitor through the solenoid, the magnetic dipole moment of this permanent magnet can be reversed. The completed attitude control system will make the first use of the low-power magnetic torquer to arrest satellite tip-off rates. It will then make the first known use of a dual axis magnetic dipole moment bias algorithm to achieve three-axis attitude alignment. The complete system is standalone for high inclination orbits, and will align the spacecraft to within 5 degrees of ram, nadir, and local vertical, without any requirement for attitude determination. The system arrests tip-off rates of up to 5� per second (in all 3 axes) for a satellite in a 600 kilometer polar orbit expending 0.56 milliwatts of power. Once in the proper alignment, it utilizes 0.028 milliwatts to maintain it. The system will function for low inclination orbits with the addition of a gravity boom. The system utilizes the magnetometer to calculate spacecraft body rates. This is the only known use of a magnetometer to directly measure spacecraft body rates without prior knowledge of spacecraft attitude.