Engineering Tools for Variable Stiffness Vibration Suppression and Isolation

With the advent of smart materials, the concept of semi-active control or dynamic control of stiffness and/or damping for vibration control of structures has become practical and has seen limited use. Semi-active control has advantages over active and passive control methods, since it provides almost as much capability as active control while requiring much less power. Its main disadvantage is its inherent nonlinearity, greatly complicating engineering design. The purpose of this research is to extend semi-active control vibration isolation tools and methods considering space launch and on-orbit systems

The Fifth NASA/DOD Controls-Structures Interaction Technology Conference, part 1

This publication is a compilation of the papers presented at the Fifth NASA/DoD Controls-Structures Interaction (CSI) Technology Conference held in Lake Tahoe, Nevada, March 3-5, 1992. The conference, which was jointly sponsored by the NASA Office of Aeronautics and Space Technology and the Department of Defense, was organized by the NASA Langley Research Center. The purpose of this conference was to report to industry, academia, and government agencies on the current status of controls-structures interaction technology. The agenda covered ground testing, integrated design, analysis, flight experiments and concepts

Classical and non-classical laser sources for current and future gravitational wave detectors

Current and future gravitational wave detectors (GWDs) place high demands on their subsystems to reach their sensitivity target. Therefore, the stabilized laser systems and squeezed light sources have to fulfill the highest requirements to allow for the anticipated sensitivity. Currently, second-generation GWDs use lasers at a wavelength of 1064 nm to measure differential arm length changes in their Michelson interferometers and since 2015 they are detecting gravitational waves. In this thesis, Nd:YVO4 solid-state laser amplifiers with output powers of up to 114 W and a very high spatial purity down to 2.9% higher order mode content were set up, tested, and integrated into a GWD laser stabilization environment. The amplifiers allowed for low noise and highly reliable operation, such that they were integrated into the laser systems of currently operating GWDs. Future ground-based third-generation GWDs, like the Einstein Telescope or Cosmic Explorer, are supposed to increase their sensitivity by more than one order of magnitude compared to the current generation. One foreseen improvement is to lower the mirrors' thermal noise by installing cryogenically-cooled silicon mirrors in some of their interferometers. Due to the required transparency of silicon, a change of the laser wavelength to either 1550 nm or 2 µm is necessary. A detailed characterization of laser sources and amplifiers at 1550 nm is presented in this thesis to select a suitable configuration for a GWD laser system at this wavelength. High-bandwidth frequency and power stabilization schemes were designed for the selected laser system, which were tailored for the needs of GWDs. These laser stabilizations were operated simultaneously and characterized by out-of-loop sensors. Independent measurements proved a shot noise limited operation of the power stabilization, below a relative power noise of 10^{-8} Hz^{-1/2} between 100 Hz to 100 kHz, and a frequency noise down to 400 mHzHz^{-1/2}, achieved with an active frequency stabilization with a unity-gain frequency above 2 MHz. The generation of strongly squeezed vacuum states of light is a key technology for current and future ground-based GWDs to reach sensitivities beyond their classical quantum noise limit. By employing the stabilized laser system in a newly designed squeezed light source, the direct measurement of up to 11.5 dB squeezing at 1550 nm wavelength over the entire detection bandwidth of future ground-based GWDs ranging from 10 kHz down to below 1 Hz was demonstrated, for the first time in literature. Furthermore, the direct observation of a quantum shot-noise reduction of up to 13.5 +/- 0.1 dB at MHz frequencies allowed to derive a precise constraint on the absolute quantum efficiency of the photodiodes used for balanced homodyne detection. All these results provide important knowledge regarding laser systems and squeezed light sources for future GWDs, as well as for the whole field of high precision metrology or cryptography, where ultra-low noise laser systems and non-classical states of light are of great interest

Technology for large space systems: A bibliography with indexes (supplement 19)

This bibliography lists 526 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1, 1988 and June 30, 1988. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system, interactive analysis and design, structural and thermal analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems

Adaptive deformable mirror : based on electromagnetic actuators

Refractive index variations in the earth's atmosphere cause wavefront aberrations and limit thereby the resolution in ground-based telescopes. With Adaptive Optics (AO) the temporally and spatially varying wavefront distortions can be corrected in real time. Most implementations in a ground based telescope include a WaveFront Sensor, a Deformable Mirror and a real time wavefront control system. The largest optical telescopes built today have a ~ 1 Om primary mirror. Telescopes with more collecting area and higher resolution are desired. ELTs are currently designed with apertures up to 42m. For these telescopes serious challenges for all parts of the AO system exist. This thesis addresses the challenges for the DM. An 8m class telescope on a representative astronomical site is the starting point. The atmosphere is characterized by the spatial and temporal spectra of Kolmogorov turbulence and the frozen flow assumption. The wavefront fitting error, caused by a limited number of actuators and the temporal error, caused by a limited control bandwidth, are the most important for the DM design. It is shown that ~5000 actuators and 200Hz closed loop bandwidth form a balanced choice between the errors and correct an 8m wavefront in the visible to nearly diffraction limited. An actuator stroke of ~5.6J.!m and ~0.36J.!m inter actuator stroke is thereby needed. Together with the nm's resolution, low power dissipation, no hysteresis and drift, these form the main DM requirements. The design, realization and tests of a new DM that meets these requirements and is extendable and scalable in mechanics, electronics and control to suit further Extremely Large Telescopes (ELTs) is presented. In the DM a few layers are distinguished: a continuous mirror facesheet, the actuator grid and the base frame. In the underlying layer - the actuator grid - low voltage electromagnetic push-pull actuators are located. Identical actuator modules, each with 61 actuators, hexagonally arranged on a 6mm pitch can be placed adjacent to form large grids. The base frame provides a stable and stiff reference. A thin facesheet is needed for low actuator forces and power dissipation, whereby its lower limit is set by the facesheets inter actuator deflection determined by gravity or wind pressure. For both scaling laws for force and dissipation are derived. Minimum power dissipation is achieved when beryllium is used for the mirror facesheet. Pyrex facesheets with 100J.!m thickness are chosen as a good practical, alternative in the prototype development. Struts (00.1 x 8mm) connect the facesheet to the actuators and ensure a smooth surface over the imposed heights and allow relative lateral movement of the facesheet and the actuator grid. Measurements show 3nm RMS surface unflattness from the glued attachment. The stiffness of the actuators form the out-of-plane constraints for the mirror facesheet and determine the mirrors first resonance frequency. and is chosen such that the resonance frequency is high enough to allow the high control bandwidth but not higher that needed to avoid excessive power dissipation and fix points in the surface in case of failure. The electromagnetic variable reluctance actuators designed, are efficient, have low moving mass and have suitable stiffness. Other advantages are the low costs, low driving voltages and negligible hysteresis and drift. The actuators consist of a closed magnetic circuit in which a PM provides static magnetic force on a ferromagnetic core that is suspended in a membrane. This attraction force is increased of decreased by a current through a coil. The actuators are free from mechanical hysteresis, friction and play and therefore have a high positioning resolution with high reproducibility. The actuator modules are build in layers to reduces the number of parts and the complexity of assembly and to improve the uniformity in properties. Dedicated communication and driver electronics are designed. FPGA implemented PWM based voltage drivers are chosen because of their high efficiency and capability to be implemented in large numbers with only a few electronic components. A multidrop LVDS based serial communication is chosen for its low power consumption, high bandwidth and consequently low latency, low communication overhead and extensive possibilities for customization. A flat-cable connects up to 32 electronics modules to a custom communications bridge, which translates the ethernet packages from the control PC into LVDS. Two DMs prototypes were successfully assembled: a 050mm DM with 61 actuators and a 0l50mm DM with 427 actuators. In the second prototype modularity is shown by the assembly of seven identical grids on a common base. The dynamic performance of each actuator is measured, including its dedicated driver and communication. All actuators were found to be functional, indicating that the manufacturing and assembly process is reliable. A nonlinear mathematical model of the actuator was derived describing both its static and dynamic behavior based on equations from the magnetic, mechanic and electric domains. The actuator model was linearized, leading to expressions for the actuator transfer function and properties such as motor constant, coil inductance, actuator stiffness and resonance frequency. From frequency response function measurements these properties showed slight deviations from the values derived from the model, but the statistical spread for the properties was small, stressing the reliability of the manufacturing and assembly process. The mean actuator stiffness and resonance frequency were 0.47kN/m and 1.8kHz respectively, which is close to their design values of 500N/m and 1.9kHz. The time domain response of an actuator to a 4Hz sine voltage was used to determine hysteresis and semi-static nonlinear response of the actuator. This showed the first to be negligible and the second to remain below 5% for ±10J.!m stroke. Measurements showed that in the expected operating range, the total power dissipation is dominated by indirect losses in FPGAs. The static DM performance is validated using interferometric measurements. The measured influence matrix is used to shape the mirror facesheet into the first 28 Zernike modes, which includes the piston term that represents the best flat mirror. The total RMS error is ~25nm for all modes. The dynamic behavior of the DM is validated by measurements. A laser vibrometer is used to measure the displacement of the mirror facesheet, while the actuators are driven by zero-mean, bandlimited, white noise voltage sequence. Using the MOESP system identification algorithm, high-order black-box models are identified with VAF values around 95%. The first resonance frequency identified is 725Hz, and lower than the 974Hz expected from the analytical model. This is attributed to the variations in actuator properties, such as actuator stiffness. The power dissipation in each actuator of the 050mm mirror to correct a typical Von Karmann turbulence spectrum is ~ 1.5m W

Technology for large space systems: A bibliography with indexes (supplement 20)

This bibliography lists 694 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System between July, 1988 and December, 1988. Its purpose is to provide helpful information to the researcher or manager engaged in the development of technologies related to large space systems. Subject areas include mission and program definition, design techniques, structural and thermal analysis, structural dynamics and control systems, electronics, advanced materials, assembly concepts, and propulsion

Design of a small fast steering mirror for airborne and aerospace applications

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 177-181).This thesis presents the analysis and design of a small advanced fast steering mirror (sAFSM) for airborne and aerospace platforms. The sAFSM provides feedback-controlled articulation of two rotational axes for precision optical pointing. The design, useful for both disturbance rejection and high-speed scanning applications, incorporates a flux steering actuator with a ring core magnetic configuration. The novel magnetic concept enables a dramatic size reduction compared with heritage systems. The moving armature is supported with a combination of elastomer sheets and active position control. Local angular and mirror-normal displacement is sensed with integrated capacitive sensors. Analysis content includes specification of performance requirements based on a realistic deep-space laser communication mission, magnetic equivalent circuit and three-dimensional magnetostatic finite element analysis of the actuator, and a 3D structural optimization of the moving armature modal frequencies. The resulting design is one iteration removed from a flight -ready model. The sAFSM hardware is in fabrication, and anticipated performance exceeds 10 krad/s2 angular acceleration, 10 mrad range, and 9 kHz closed-loop bandwidth.by Michael Thomas Boulet.S.M

Modeling, Analysis, and Optimization Issues for Large Space Structures

Topics concerning the modeling, analysis, and optimization of large space structures are discussed including structure-control interaction, structural and structural dynamics modeling, thermal analysis, testing, and design

Space Station Systems: a Bibliography with Indexes (Supplement 8)

This bibliography lists 950 reports, articles, and other documents introduced into the NASA scientific and technical information system between July 1, 1989 and December 31, 1989. Its purpose is to provide helpful information to researchers, designers and managers engaged in Space Station technology development and mission design. Coverage includes documents that define major systems and subsystems related to structures and dynamic control, electronics and power supplies, propulsion, and payload integration. In addition, orbital construction methods, servicing and support requirements, procedures and operations, and missions for the current and future Space Station are included