The error mean and standard deviations were calculated  using the statistics of the angular position data at the end  of a 10-second step-and-hold for both large and small  steps. This is not absolute mirror pointing accuracy, but rather the tracking error between the commanded angle  and the angle measured by the encoder for azimuth and  the wedge sensor for elevation. Absolute pointing accuracy, as measured with the theodolite, was about 0.03  deg at room temperature.   The azimuth error is largely due to the limited counts of the  encoder, 288000 counts over 360 deg of rotation, which  results in 4.5 arcsec/count. The encoder toggles by one  count during steady state, resulting in the error.  The elevation axis is extremely repeatable, as shown by  the small mean error; however, the noise, represented by the error standard deviation, is larger than desired. The  noise is attributed mainly to the 16-bit A/D computer card’s  peak-to-peak noise of over 15 counts, as claimed in the card manufacturer’s specification sheet. This equates to  about 25 arcsec of peak-to-peak noise, when the 16-bit resolution is applied to the full 30-deg mechanical  angle of the elevation axis. Some noise is also gener ated by the wedge sensor electronics box. A digital  moving average filter was applied to the wedge sensor feedback, which helped considerably. The control  algorithm also contains a derivative term in the forward loop, which tends to enhance the noise.  The closed-loop bandwidth for each axis, as measured using the control systems analyzer, was about 70  Hz at the -3 dB point. The gain margin of 6 dB was verified by doubling the control algorithm gains in  each axis and performing a step response test to determine that the system remained stable, which it did.   FSM Portable Demonstration  Figure 15 shows the FSM portable demonstration system, which includes t he FSM, the breadboard  electronics, the host and target computers, and a laser for “light show” demonstrations. The system was  programmed to project a Lissajous figure and an “S” figure on the ceiling at high frequencies, and also to do slow scans for audience visualization.   Wedge Sensor Temperature Mapping  The current wedge senso r for feedback experiences drift with  temperature, so a mapping was performed to show feasibility of  achieving high absolute pointing accuracy. One possible application of the FSM requires a ±50-arcsec absolute pointing  accuracy over a 0-40°C temperature range. The angle was  measured using an autocollimator and mapped versus sensor voltage and temperature. Figure 16 shows that the results  appear predictable and highly repeatable, verifying feasibility of  mapping.  Table 5. Performance Specifications  of Final Prototype  Specification Value Aperture (mm) 75 Mass (electronics not included) (kg) 1.0 Avg. Power (W) 0.4 Peak Power (W) 30 Azimuth Rot. (mechanical deg) ±60 Elevation Rot. (mechanical deg) ±15 Azimuth Error Mean (arcsec) <1 Azimuth Error Std. Dev. (arcsec) <3 Elevation Error Mean (arcsec) <0.05 Elevation Error Std. Dev. (arcsec) <6.5 Azimuth Slew Rate (0-100%) (deg/sec) 160 Elevation Slew Rate (0-100%) (deg/sec) 75 Bandwidth (Hz, 100 arcsec amplitude) 70 Gain Margin (dB) 6 Figure 15. Portable Demonstration 396