The data processing circuit to obtain sun orientation error voltage applied for the 3-axis attitude control system of the K-10-11 rocket is described. 2-set of four solar cells are utilized for sources of each fine and coarse attitude error sensors. A combination of sum and/or difference of 4 of solar cells produces pitch and yaw error voltage outputs. Then combination of fine and coarse error outputs provides the sensitivity of 2.5 V/degree about zero error position. and the output voltage greater than 4 volts having proper polarity up to ±90° error angle. From flight test results, the offset voltage appeared in the output of this processing circuit was about 40 mV (1 arc-sec in sun orientation error) and the unbalance in solar cell outputs induced from solar intensity variation was estimated.