Miniature Satellite Attitude Stabilization using Magnetic Torquer and Solar Radiation Pressure

Paper number

IAC-07-D1.2.03

Author

Dr. Krishna Kumar, Ryerson University, Canada

Year

2007

Abstract

The attitude stability of satellites is of considerable importance for successful completion of a space mission. Magnetic torquers have been applied for the attitude control and momentum dumping of satellites. They are relatively reliable, lightweight, and energy efficient. Particularly, in small satellites where the traditional attitude stabilization systems such as reaction wheels (momentum wheels) do not fit within the limited weight and power budget and therefore, are impractical, the magnetic torquers have been very attractive. However, the magnetic torquers alone can not guarantee global stability because of their inability to provide torque about the local magnetic field direction, for example, the pitch attitude of an equatorial orbit satellite can not be controlled.  The solar radiation pressure (SRP) has been proposed for attitude control of high altitude satellites and interplanetary probes. However, the SRP alone can not effectively stabilize three-dimensional attitude of non-axisymmetric satellites with only a single pair of solar panels.

In the present paper, we consider SRP and magnetic torquer together for a three-axis attitude control of an equatorial high-Earth orbit satellite.  The present study makes several contributions. First, the satellite pitch and roll attitudes are stabilized by rotating a pair of control surfaces using respective motor about two satellite-body axes instead of one-axis or instead of using several pairs of control surfaces. Second, the yaw attitude is controlled by a magnetic torquer. Third, various uncertainties in the system parameters have been considered and the proposed controller performance is tested in the presence of these uncertainties. For example, surface areas exposed to impinging photons of the two-oppositely placed solar panels, in practice, may not be exactly same as well as the distances of their centers of pressure might not be equal. In addition to these uncertainties, the moments of inertia of the system may differ from the designed exact inertia and the products of inertia might not be exactly zero. Furthermore, the orbital eccentricity may not be zero and in the solar pressure model, the fraction of impinging photos specularly reflected may not be one. In fact, these uncertainties can easily destabilize the system which was otherwise stable. Finally, the attitude control of satellites in eccentric orbits by rotating the control surfaces have not yet been discussed in the literature. 

The proposed system is comprised of a satellite, a pair of solar panels oppositely attached on the satellite body along its yaw-axis, and a magnetic torquer. The Euler method is utilized to obtain the governing nonlinear equations of motion for the proposed system moving in an elliptic orbit.  The control laws are developed for suitable rotations of solar panels and variations in magnetic moment. For a detailed assessment of the proposed attitude control strategy, the set of governing equations of motion is numerically integrated and the efficacy of the proposed controller is examined considering various parameters including orbital eccentricity, satellite inertia matrix, solar panels parameters, and the Earth’s shadow as well as uncertainties in the system parameters. The SRP torque is found to be successful in controlling the satellite pitch and roll attitudes while the yaw attitude was stabilized by the magnetic torquer. It is to be noted that the satellite attitude is stabilized within half an orbit and it remained within a fraction of a degree. The control inputs are found to be within the limits of the maximum solar panels rotation of 40 deg and with the maximum magnetic rod magnetic moment of 12 Ampere-square meter. Thus, the nearly passive nature of the proposed controller makes it highly useful for the space mission.

Abstract document

IAC-07-D1.2.03.pdf

Manuscript document

IAC-07-D1.2.03.pdf (🔒 authorized access only).

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