Development of a Low-Cost Fine Steering Mirror

The Space Dynamics Laboratory has used internal funds to develop a prototype low-cost two-axis fine steering mirror (FSM) for space-based and airborne applications. The FSM has a lightweight 75 mm-by150-mm high-reflectance mirror, high angular deflection capability for along-track ground motion compensation and cross-track pointing, and a 70-Hertz bandwidth for small amplitudes to help cancel unwanted jitter. It makes use of off-the-shelf components as much as possible. Key performance parameters are: Clear aperture, 75 mm; elevation angle, ±15 deg (mechanical); azimuth angle, ±60 deg (mechanical); slew rate, greater than 75 deg/sec; bandwidth, 70 Hz; steady-state average error, about 1 arcsec; average power dissipation, 0.4 Watts; mirror surface, figure, <0.1 waves RMS; and total mechanical mass, 1 kg. Key components for the elevation axis include a rotary voice coil and a unique patent-pending non-contact feedback sensor. The azimuth axis features a brushless DC motor and a high-resolution optical encoder. Rapid prototyping, autocoding, and real-time hardware-in-the-loop (HIL) testing were used to develop the control algorithms. Additional accomplishments include temperature mapping of the feedback sensor, inventing a successful passive launch lock, launch vibration testing, and subjecting the system to a space-like environment at pressures down to 1e-7 torr and temperatures down to 164 K.