Yaw Control - A Simple Way to Enhance Solar Array Performance

Solar cell arrays are used on substantially all earth orbiting spacecraft to produce electric power. Solar arrays are of three geometric types: planar, cylindrical, and omnidirectional oriented planar arrays have a geometric efficiency (ratio of solar energy capture area to total array area) of one and are used on most large spacecraft. Cylindrical arrays which have a geometric efficiency of l/π are common on spinners while most small spacecraft including those that are earth pointed use omnidirectional arrays which have a geometric efficiency of only 1/4. An earth oriented spacecraft with a body fixed planar array can achieve a geometric array efficiency of 2/π by the simple expedient of yaw control (control about the local vertical). Body rates and torque requirements for this type of control are modest and can be provided by a variety of techniques. Parametric evaluation of this method of control is presented and various implementation schemes are discussed.