Active Feedforward Disturbance Control System

PatentNoise effects in a signal for driving a plant are reduced by generating a reference signal from the error signal. A signal generator generates a reference signal for input to a finite impulse response (FIR) filter. The error signal is produced by differencing the transfer function output and a disturbance signal. The error signal is input to the signal generator and to a least mean square calculator. The reference signal is input to a copy of the transfer function that outputs a modified reference signal. The modified reference signal is input to least mean square calculator. An LMS signal that updates the filter coefficients to minimize the mean square error is calculated and the LMS signal and the reference signal are input to the FIR filter with the FIR filter being arranged to process the LMS signal and the reference signal to minimize the error signal

Improved Hamiltonian Adaptive Control of spacecraft

The article of record as published may be found athttps://doi.org/10.1109/AERO.2009.4839565Spacecraft control is complicated by on-orbit inertia uncertainties. Considerable initial, on-orbit check-out time is required for identification of accurate system models enabling fine pointing. Smart, plug-n-play control algorithms should formulate smart control signals regardless of inertia. Adaptive control techniques provide such promise. Spacecraft control has been proposed to be adapted in the inertial frame based on estimated inertia to minimize tracking error. Due to unwieldy computations, later researchers suggested adapting the control in the body frame. This paper derives this later suggested approach using the recommended 9-parameter regression model for 3-axis spacecraft rotational maneuvers. Additionally, a new 6-parameter regression model is shown to be equivalent. A new, further-reduced 3-parameter regression model is demonstrated to yield similar performance. A new improved, simplified adaptive feedforward technique is developed and shown to provide superior performance. Following promising simulations, experimental verification is performed on a free-floating three-axis spacecraft simulator actuated by non-redundant, single-gimbaled control moment gyroscopes

Experiments on Jerk-Limited Slew Maneuvers of a Flexible Spacecraft

The article of record as published may be found at http://dx.doi.org/10.2514/6.2006-618

Applications of tuned mass dampers to improve performance of large space mirrors

In order for future imaging spacecraft to meet higher resolution imaging capability, it will be necessary to build large space telescopes with primary mirror diameters that range from 10m to 20 m and do so with nanometers surafce accuracy. Due to launch vehicle mass and volume constraints, these mirrors have to be deployable and lightweight, such as segmented mirrors using active optics to correct mirror surfaces with closed loop control. As a part of this work, system identification tests revealed that dynamic disturbances inheret in a laboratory environment are significant enough to degrade the optical performance of the telescope. Research was performed at the Naval Postgraduate School to identify the vibration modes most affecting the optical performance and evaluate different techniques to increase damping of those modes. Based on this work, tuned mass dampers (TMDs) were selected becaues of their simplicity in implementation and effectiveness in targeting specific modes. The selected damping mechanism was an eddy current damper where the damping and frequency of the damper could be easily changed. System identification of segments was performed to derive TMD specifications. Several configurations of the damper were evaluated, including the number and placement of TMDs, damping constant, and targeted structural modes. The final configuration consisted of two dampers located at the edge of each segment and resulted in the 80% reduction in vibrations. The WFE for the system without dampers was 1.5 waves, with one TMD and the WFE was 0.9 waves, and the two TMDs and the WFE was 0.25 waves. This paper provides details of some of the work done in this area and includes theoretical predictions for optimum damping which were experimentally verified on a large aperture segmented system.The authors would like to sincerely acknowledge the contribution of the members of NPS Spacecraft Reserarch and Design Center (SRDC) and the Adaptive Optics Center of Excellence (AOCoE). Research presented in this work was also conducted in collaboration with the Air Force Institute of Technology (AFIT), CSA Engineering, a Moog company,and Boeing SVS

Dynamics and Control Challenges for Imaging Satellites

Third IAA Conference on Dynamics and Control of Space SystemsImaging satellites have several challenges in dynamics and control to meet high performance requirements. As an example, Hubble Space Telescope pointing requirements are of 0.012 arc-sec and jitter requirements not to exceed 0.007 arc-sec. These satellites require fast slew maneuver with minimum slew time. Flexibility/control interaction becomes critical for these satellites. These satellites require fine mirror surfaces for diffraction limited performance. For visible images, the surface mirror accuracy requirements are a minimum of 30 nm. In order to meet these performance requirements, advance dynamics and control techniques and actuators and sensors are required. Meeting these requirements becomes even more challenging for future imaging satellites as the diameter of primary mirrors increases, resulting in deployable mirrors. This paper provides an overview of advanced dynamics and control techniques for jitter control, flexibility/control interactions, slew maneuvers, and reflector active surface control

Experimental Study of Active Vibration Suppression of Flexible Structure using Modular Control Patch

The article of record as published may be found at http://dx.doi.org/10.1109/AERO.1998.686818This paper presents experimental results of vibration suppressicln of a flexible structure using a miniaturized digital controller, called Modular Control Patch (MCP). The h4CP employs a TIC30 digital signal processor and was developed by TRW for the United States Air Force for future space vibration control. In this research, the MCP is used to implement different control algorithms for vibration suppression of a cantilevered aluminum beam with piezoceramic sensors and actuators. Positive Position Feedback (PPF) control, Strain Rate Feedback (SRF) control, and their combinations were implemented. Expenments found that PPF control is most effective for single- mode vibration suppression, and two PPF filters in parallel are most effective for multi-mode vibration suppression. Further experiments demonstrated the robustness of PPF control. PPF can achieve effective vibration suppression when there is a 20% error in modal frequency

Method and apparatus for singularity avoidance for control moment gyroscope (CMG) systems without using null motion

PatentA method is described for avoiding gyrocopic singularities during attitude correction to a sytem, such as a spacecraft having a CMG array. The method receives a corrective torque vector µ and gimbal angle values δ for each of at least three gimbal within the CMG array. The method a a Jacobian matrix A as a function of gimbal angle value δ. A. lf the determinant is not equal to zero, it is not singular, and the method calculate a gimbal rate δ using a using a pseudo-inverse steering law equation. lf the determinant is equal to zero, it is singular, and the method calculate a gimbal rate δ using a singularity avoidance steering law equation. The gimbal rate δ is output and can be applied to a CMG array resulting in applied torque to a spacecraft and attitude correction