Optical Beam Control Testbeds
18 Aug 2008-
TL;DR: In this article, two optical beam control testbeds were developed at the Spacecraft Research and Design Center, Naval Postgraduate School, to evaluate and develop control techniques for jitter and adaptive optics control.
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.
Citations
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11 Jun 2009
TL;DR: Several techniques have been developed to reduce jitter in the optical beam by using fast steering mirrors as discussed by the authors, such as increasing damping of the spacecraft support structure to reduce vibration response by adding passive and/or active damping.
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.
29 citations
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
TL;DR: In this paper, 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 terminals.
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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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.
158 citations
07 Nov 2002
TL;DR: In this paper, a design for an adaptive optics system that utilizes modern H/sub /spl infin// control theory to optimize the robustness of the system is presented for real-time correction of blurred images and have applications in astronomical imaging, freespace optical communications and high-energy laser beam guidance.
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.
16 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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03 Apr 2008
TL;DR: In this paper, a wavefront control method for the Naval Postgraduate School adaptive optics testbed is developed to remove structural noise from the flexible optical surface using discrete time proportional integral control with second order filters.
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