Spacecraft Optical Beam Jitter Control
- Paper number
IAC-05-C1.3.07
- Author
Prof. Brij Agrawal, Naval Postgraduate School, United States
- Year
2005
- Abstract
For many future space missions, the optical beam pointing requirements will be in sub-micro-radians and the jitter requirements in nano-radians. In order to achieve these performance requirements, the spacecraft attitude control is divided into two parts: large angular motion and coarse pointing is provided by the spacecraft bus and fine pointing is provided in the optical payload by fast steering mirrors. This paper presents of the results of the research done at the Spacecraft Research and Design Center for optical beam jitter control using adaptive control techniques. A laser Jitter Control Test bed was also developed at the center to validate these techniques. The test bed components are mounted on a Newport Optical Bench to isolate the components from the external vibration. The components consist of a laser source, a disturbance injection fast steering mirror (DFSM), a control fast steering mirror, a reference signal Position Sensing Detector (PSD) , a target jitter PSD, and a vibrating platform. The disturbances were both sinusoidal and random. Several adaptive control techniques, such as Least Mean Square (LMS) and Lattice Filter, and Linear Quadratic Regulator (LQR) were applied for jitter control. Improvement in LMS techniques to improve convergence rate was achieved by adding Adaptive Bias Filters (ABF) to the reference signal. In the experiments, the platform is vibrated at 50 and 87 Hz. In addition, the DFSM is used to inject a random component of 200 Hz band-limited white noise. The experimental results demonstrated that the addition of ABS filter to LMS significantly increased the converging rate of the jitter. In order to achieve the reduction of both sinusoidal and random jitter, a combination of ABF/LMS and LQR is most effective. The ABF/LMS control is most effective for a sinusoidal jitter and the LQR control for a random jitter.
- Abstract document