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Proceedings ArticleDOI

Optical Beam Control Testbeds

18 Aug 2008-

Abstract: This paper discusses two optical beam control testbeds developed at the Spacecraft Research and Design Center, Naval Postgraduate School, to evaluate and develop control techniques for jitter and adaptive optics control. The first testbed, a Jitter Control Testbed is used to develop control techniques for optical beam jitter. In the second testbed, the Adaptive Optics Testbed, adaptive optics control techniques are used to control the surfaces of a segmented mirror with the objective of minimizing aberrations in the images. This paper will also discuss the evaluation of different control techniques used in jitter and adaptive optics control.

Topics: Adaptive control (59%), Jitter (57%), Adaptive optics (55%), Testbed (55%)

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Citations
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Proceedings ArticleDOI
11 Jun 2009
Abstract: The current imaging spacecraft design trend is for higher imaging performance, allowing very low jitter. Vibration sources on spacecraft include reaction or momentum wheels, control moment gyros (CMG), solar drive motors, thruster firing, cryogenic coolers and slew maneuvers. Several techniques have been developed to reduce jitter. One technique is to increase damping of the spacecraft support structure to reduce vibration response by adding passive and/or active damping. The second technique is to introduce isolation between vibration source and the spacecraft. The third technique is to isolate the optical payloads from the spacecraft. The fourth technique is to reduce jitter in the optical beam by using fast steering mirrors. For spacecraft requiring the very low jitter, a combination of these techniques is used. This paper discusses briefly all these jitter control techniques.

26 citations


Proceedings ArticleDOI
18 Aug 2011
TL;DR: The Filtered-X Least Mean Square adaptive filter with bias integration technique is applied to an adaptive optics system where the Discrete Fourier Transform is used to project the measured phase onto the Fourier basis for modal control.
Abstract: In this paper, the Filtered-X Least Mean Square (FXLMS) adaptive filter with bias integration technique is applied to an adaptive optics system where the Discrete Fourier Transform is used to project the measured phase onto the Fourier basis for modal control. The control law is applied in the complex-valued coefficient space and the FXLMS algorithm is modified accordingly for the complex-valued control. Numerical analysis is conducted for a feedback loop of a single Fourier mode in the presence of a disturbance representing a frozen flow atmospheric turbulence. The performance is compared with a Kalman estimator based control law proposed in the literature called Predictive Fourier Control (PFC). The proposed method demonstrated a similar performance for a stationary disturbance and improved performance for a slowly drifting disturbance. Whereas the performance of the PFC is very sensitive to the accuracy of the identification of the disturbance, the proposed method does not require such an explicit identification and produces minimum error for the given disturbance.

3 citations


Cites background from "Optical Beam Control Testbeds"

  • ...In recent years, control techniques that are more advanced than a simple classical control have been proposed [1-10]....

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Patent
01 Sep 2009
Abstract: A method for pointing control of a laser communication terminal on a spacecraft may include measuring a line-of-sight (LOS) error of the laser communication terminal. The method may also include estimating a LOS error of the laser communication terminal based on measurements from a spacecraft gyro and a gimbal gyro onboard the spacecraft. The method may further include switching from a LOS error measurement feedback to a LOS error estimate feedback to control pointing of the laser communication terminal during a power fade condition.

1 citations


References
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Journal ArticleDOI
TL;DR: An adaptive experimental system to compensate for the wave-front aberrations of a model eye has been built in which the developed adaptive mirror-control algorithm is used to control a deformable mirror with 19 active channels.
Abstract: The nonlinear response and strong coupling of control channels in micromachined membrane deformable mirror (MMDM) devices make it difficult for one to control the MMDM to obtain the desired mirror surface shapes. A closed-loop adaptive control algorithm is developed for a continuous-surface MMDM used for aberration compensation. The algorithm iteratively adjusts the control voltages of all electrodes to reduce the variance of the optical wave front measured with a Hartmann–Shack wave-front sensor. Zernike polynomials are used to represent the mirror surface shape as well as the optical wave front. An adaptive experimental system to compensate for the wave-front aberrations of a model eye has been built in which the developed adaptive mirror-control algorithm is used to control a deformable mirror with 19 active channels. The experimental results show that the algorithm can adaptively update control voltages to generate an optimum continuous mirror surface profile, compensating for the aberrations within the operating range of the deformable mirror.

155 citations


Proceedings ArticleDOI
07 Nov 2002
Abstract: Adaptive optics systems are concerned with the real-time correction of blurred images and have applications in astronomical imaging, freespace optical communications and high-energy laser beam guidance. This paper outlines the proposed design for an adaptive optics system that utilizes modern H/sub /spl infin// control theory to optimize the robustness of the system.

15 citations


"Optical Beam Control Testbeds" refers methods in this paper

  • ...QQ = −− − ( 6 ) Fig 3 shows the block diagram of the Filtered-X LMS (FXLMS) method....

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Proceedings ArticleDOI
03 Apr 2008
Abstract: Future space based deployable telescopes will be subject to non-atmospheric disturbances. Jitter and optical misalignment on a spacecraft can be caused by mechanical noise of the spacecraft, and settling after maneuvers. The introduction of optical misalignment and jitter can reduce the performance of an optical system resulting in pointing error and contributing to higher order aberrations. Adaptive optics can be used to control jitter and higher order aberrations in an optical system. In this paper, wavefront control methods for the Naval Postgraduate School adaptive optics testbed are developed. The focus is on removing structural noise from the flexible optical surface using discrete time proportional integral control with second order filters. Experiments using the adaptive optics testbed successfully demonstrate wavefront control methods, including a combined iterative feedback and gradient control technique. This control technique results in a three time improvement in RMS wavefront error over the individual controllers correcting from a biased mirror position. Second order discrete time notch filters are also used to remove induced low frequency actuator and sensor noise at 2Hz. Additionally a 2 Hz structural disturbance is simulated on a Micromachined Membrane Deformable Mirror and removed using discrete time notch filters combined with an iterative closed loop feedback controller, showing a 36 time improvement in RMS wavefront error over the iterative closed loop feedback alone.

7 citations