James A. King

Application of maximum entropy optimal projection design synthesis to a benchmark problem

Maximum entropy/optimal projection design synthesis is a methodology for designing robust, fixed-order controllers for flexible structures. This paper reviews the theoretical basis for this method and illustrates the approach using a benchmark problem. The benchmark problem involves two masses with spring coupling, an uncertain spring constant, and a sensor and actuator that are noncollocated. The results of this paper also illustrate the use of a precompensation methodology that allows the control designer to precondition the design plant by embedding judiciously designed filters. These filters are included in the implemented controller.

High performance, accelerometer-based control of the Mini-MAST structure

Many large space system concepts will require active vibration control to satisfy critical performance requirements such as line of sight pointing accuracy and constraints on rms surface roughness. In order for these concepts to become operational, it is imperative that the benefits of active vibration control be shown to be practical in ground based experiments. The results of an experiment shows the successful application of the Maximum Entropy/Optimal Projection control design methodology to active vibration control for a flexible structure. The testbed is the Mini-Mast structure at NASA-Langley and has features dynamically traceable to future space systems. To maximize traceability to real flight systems, the controllers were designed and implemented using sensors (four accelerometers and one rate gyro) that are actually mounted to the structure. Ground mounted displacement sensors that could greatly ease the control design task were available but were used only for performance evaluation. The use of the accelerometers increased the potential of destabilizing the system due to spillover effects and motivated the use of precompensation strategy to achieve sufficient compensator roll-off.

Transport of energy by ultraintense laser-generated electrons in nail-wire targets

Nail-wire targets (20 μm diameter copper wires with 80 μm hemispherical head) were used to investigate energy transport by relativistic fast electrons generated in intense laser-plasma interactions. The targets were irradiated using the 300 J, 1 ps, and 2×1020 W⋅cm−2 Vulcan laser at the Rutherford Appleton Laboratory. A spherically bent crystal imager, a highly ordered pyrolytic graphite spectrometer, and single photon counting charge-coupled device gave absolute Cu Kα measurements. Results show a concentration of energy deposition in the head and an approximately exponential fall-off along the wire with about 60 μm 1/e decay length due to resistive inhibition. The coupling efficiency to the wire was 3.3±1.7% with an average hot electron temperature of 620±125 keV. Extreme ultraviolet images (68 and 256 eV) indicate additional heating of a thin surface layer of the wire. Modeling using the hybrid E-PLAS code has been compared with the experimental data, showing evidence of resistive heating, magnetic trap...

Autonomous system identification and control of MACE II using the Frequency Domain Expert algorithm

The Frequency Domain Expert (FDE) adaptive identification and control design algorithm will be applied to the Middeck Active Control Experiment (MACE) during a re-flight of the experiment. FDE was recently developed by the authors to address the need for an algorithm that requires only local measurement, has predictable convergence properties, and yields performance in terms easily understood by controls system engineers. Ground testing to date has produced FDE controllers that reduce line-of-sight error by more than 22 dB, only a few dB less than the best performance attained via offline, fixed-gain LQG controllers during the original MACE flight.

Active vibration isolation with stiff actuators and inertial sensors

Operation of sensitive equipment aboard multi-sensor platforms requires active vibration isolation technology. In response to these needs, the active isolation fitting (AIF) was developed to replace passive mechanical end fittings and joints in truss structures. The AIF combines intrastructural and inertial devices to cancel vibration transmission into a vibration-sensitive subsystem. This paper discusses the AIF principles of operation, details its robust performance characteristics and reviews the extensive experimental results that have been accumulated over the past several years. Test results show 20 to 30 dB of broadband isolation for both single AIF tests and six degree-of-freedom isolation systems demonstrated on two major, government- supplied testbeds.

The Multi-Hex Prototype Experiment

The authors describe the Multi-Hex Prototype Experiment (MHPE), which was developed to experimentally investigate the technologies associated with the active control of flexible structures. The MHPE has as its main component a structure that was designed to emulate the generic properties of large space structures, such as high-frequency RF or optical antennas and solar concentrators. The authors describe the primary features of the MHPE and present some experimental results which illustrate the efficacy of system identification and active control. Experimentation has provided validation of system identification using the eigensystem realization algorithm and has also shown the ability of active control to provide significant vibration attenuation.<<ETX>>

In flight autonomous system identification and control of MACE II using the frequency domain expert algorithm

The Frequency Domain Expert (FDE) adaptive identification and control design algorithm will be applied to the M iddeck Active Control Experiment (MACE) during a re-flight of the experiment. FDE was recently developed by the authors to address the need for an algorithm that requires only local measurement, has predictable convergence properties, and yields performance in terms easily understood by controls system engineers. Ground testing to date has produced FDE controllers that reduce line-of-sight error by more than 22 dB, only a few dB less than the best performance attained via offline, fixed-gain LQG controllers during the original MACE flight.

Decentralized adaptive neural control for distributed mesoscale actuators and sensors

This paper discusses the Adaptive Neural Control (ANC) Architecture for on-line system identification and adaptive control. After reviewing results to-date involving control of structural vibration, we describe extensions of the ANC architecture to handle adaptive control of smart structures involving large numbers of distributed actuators and sensors.

X-ray calibration and characterization at National Security Technologies, LLC Livermore Operations

X-ray calibration is a primary component of the calibration services provided by National Security Technologies, LLC (NSTec) Livermore Operations (LO). The X-ray calibration labs at NSTec LO consist of four labs which provide characteristic and bremsstrahlung X-ray output beams ranging in energy from 300 eV to 110 keV. These labs can calibrate a variety of X-ray detectors and components including CCD’s, streak cameras, spectrometers, and filters. Many of the calibration measurements are NIST-traceable. Calibrations and characterizations provided include quantum efficiency, sensitivity, dynamic range, resolution, flat-field test, and transmission measurements. Historically, these labs have performed calibrations for various institutions and national laboratories such as LLNL, LANL, and Sandia. In addition, NSTec (LO) has diagnostic R&D capabilities such as extending curved crystal X-ray imaging to higher energies. This presentation will describe the services provided by these labs, the operation and in-house, NVLAP certified calibration of the various X-ray sources and diagnostics used, and the general layout of the NSTec (LO) X-ray labs.

X-ray doppler velocimetry for diagnosis of fluid motion in ICF implosions

We are developing a novel diagnostic for measurement of bulk fluid motion in materials, that is particularly applicable to very hot, x-ray emitting plasmas in the High Energy Density Physics (HEDP) regime. The X-ray Doppler Velocimetry (XDV) technique relies on monochromatic imaging in multiple x-ray energy bands near the center of an x-ray emission line in a plasma, and utilizes bent imaging crystals. Higher energy bands are preferentially sensitive to plasma moving towards the viewer, while lower energy bands are preferentially sensitive to plasma moving away from the viewer. Combining multiple images in different energy bands allows for a reconstruction of the fluid velocity field integrated along the line of sight. We review the technique, and we discuss progress towards benchmarking the technique with proof-of-principle HEDP experiments.