Viking Thrust Vector Control Dynamics Using Hybrid Coordinates to Model Vehicle Flexibility and Propellant Slosh

Control System Design Implementation of the linear feedback control system with time varying feedback gains and command forces may be accomplished with a fairly simple analog controller. The feedback gains and command forces consist of well behaved sinusoidal functions, constants, and simple ramp functions. The difficulty caused by the gain fluctuation near the simulation final time may be overcome by cycling the control gain functions back to the beginning before the fluctuations take place. Cycling the control gain functions is not a problem because the control is in a feedback form. The effect of cycling the control gain functions may be interpreted in the analysis as restarting the nonlinear simulation with an initial state closer to the final state. Simulation of the nonlinear system within the region of operation always resulted in a stable response so the effect of restarting the simulation when the system state has moved closer to the final state is valid. A consequence of cycling the control is that the functional in Eq. Conclusions This study has shown that the dynamic instability caused by sloshing fluid stores carried in the main rigid body of a spacecraft may be controlled by use of a linear quadratic regulator with the fluid modeled as an equivalent spherical pendulum and only the first mode of fluid oscillation included. The control system presented stabilized a highly nonlinear system for a large deviation from the nominal operating point and uses easily measured state variables (only main body fixed angular rates and attitude) and was shown to be stable for a wide variation in fluid level. It was shown that sensing the dynamic state of the fluid was not necessary for the specific spacecraft under study. A pointing maneuver was also successfully accomplished by this control system and a control design based on the analysis was outlined for the specific spacecraft. Acknowledgments This study was completed under partial support of contract no. AFOSR-86-0080 and subcontract 83RIP33, U.S. Air Force. The authors wish to acknowledge the support of Iowa State University in accomplishing the lengthy digital computer simulation required in this study. References Introduction An interesting problem in robotics is cloth handling. Applications include composite lay-up and apparel and upholstery manufacturing. Rebman (1986) describes an application of a tactile sensor to assembly of a flexible diaphram and a plastic cap. Hertzanu and Tabak (1986) described an adaptive controller for an industrial sewing machine. For most applications, cloth must be held taut and unwrinkled. It was postulated that this requires multi-axis force control, and a suitable control system was designed and constructed. The system chosen is an adaptive force feedback loop with position accommodation. Non-adaptive force feedback control schemes have been described and tested by many researchers, such as Whitney (1977). An adaptive force feedback loop for coordination of two robot arms was described by Because cloth stiffness varies depending on whether the individual cloth fibers are taut or slack, a nonadaptive loop is unsuitable for cloth handling. An adaptive control loop was designed with cloth stiffness as the adaptive variable. The system design was constructed and tested using a PUMA 560 robot with a LORD 15/50 force/torque sensor mounted on its wrist. Control System Description The parameter estimator is a least mean square (LMS) estimator. Let y=KH(z)u = K a x z ' + + a"z~ -r-"u, \+b x z + ... +b"z~ where a it ..., a" and b\ b" axe found from the ordinary least squares plant identification, y is the error in the force, and u is the position command. Then the LMS estimator for A-is K* =K*^i+r{y-y*)w-l , where K* is the estimated stiffness, +a"u""), and Vf_ 1 =ff 1 «_ 1 + The position control law is where u, is the change in the position of the /th degree of freedom (DOF), y t is the force (or torque) error of the ith DOF, and K* is the stiffness of the rth DOF. end of a cloth of dimensions 36 by 36 in., the other end of which was attached to a table. Both ends of the cloth were stapled to wooden rods; proper robot end effectors would eliminate the need for these rods. Two 8086 microprocessor cards were also built. The 1st microprocessor calculated the cloth stiffness and end effector position changes; the 2nd microprocessor was used for communication with the robot and the force/torque sensor. Experimental Procedure The experiments were run with one end of the cloth fixed. The initial slack and misalignments of the cloth were as follows: Stretch (x) direction Lateral (y) direction 6 direction 6 to 10 in. of slack 2 to 4 in. of misalignment 5° to 20° of misalignment The robot straightened out the misalignments and pulled 4 lb of tension on the cloth. After it had done so the end effector was moved inward to produce 6 in. of slack in the x-direction. This movement draped the cloth over 2 boxes without wrinkling. Test Setup Experimental Results The visual results showed consistency between the experiments. In all of them, the cloth was successfully draped over the boxes without wrinkles, the motion was smooth, and the times were approximately the same. Transactions of the ASME position, the robot pulls a 4 lb tension on the cloth and adjusts the lateral (y) force and the moment to zero. This requires approximately 12 s. At 14 s the robot drapes the cloth; at this point the tension (x-force) falls to zero. This experiment was successfully repeated several times. Conclusions A force feedback control loop implemented on a robot has been used successfully to straighten and draw a tension on a cloth. Further work will include using more sophisticated end effectors to grip the cloth, and applications in upholstery and composite manufacture. Reference

The LUX-ZEPLIN (LZ) Experiment

We describe the design and assembly of the LUX-ZEPLIN experiment, a direct detection search for cosmic WIMP dark matter particles. The centerpiece of the experiment is a large liquid xenon time projection chamber sensitive to low energy nuclear recoils. Rejection of backgrounds is enhanced by a Xe skin veto detector and by a liquid scintillator Outer Detector loaded with gadolinium for efficient neutron capture and tagging. LZ is located in the Davis Cavern at the 4850' level of the Sanford Underground Research Facility in Lead, South Dakota, USA. We describe the major subsystems of the experiment and its key design features and requirements

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

The LUX-ZEPLIN (LZ) experiment

We describe the design and assembly of the LUX-ZEPLIN experiment, a direct detection search for cosmic WIMP dark matter particles. The centerpiece of the experiment is a large liquid xenon time projection chamber sensitive to low energy nuclear recoils. Rejection of backgrounds is enhanced by a Xe skin veto detector and by a liquid scintillator Outer Detector loaded with gadolinium for efficient neutron capture and tagging. LZ is located in the Davis Cavern at the 4850’ level of the Sanford Underground Research Facility in Lead, South Dakota, USA. We describe the major subsystems of the experiment and its key design features and requirements

The LUX-ZEPLIN (LZ) radioactivity and cleanliness control programs

LUX-ZEPLIN (LZ) is a second-generation direct dark matter experiment with spin-independent WIMP-nucleon scattering sensitivity above 1.4×10−48cm2 for a WIMP mass of 40GeV/c2 and a 1000days exposure. LZ achieves this sensitivity through a combination of a large 5.6t fiducial volume, active inner and outer veto systems, and radio-pure construction using materials with inherently low radioactivity content. The LZ collaboration performed an extensive radioassay campaign over a period of six years to inform material selection for construction and provide an input to the experimental background model against which any possible signal excess may be evaluated. The campaign and its results are described in this paper. We present assays of dust and radon daughters depositing on the surface of components as well as cleanliness controls necessary to maintain background expectations through detector construction and assembly. Finally, examples from the campaign to highlight fixed contaminant radioassays for the LZ photomultiplier tubes, quality control and quality assurance procedures through fabrication, radon emanation measurements of major sub-systems, and bespoke detector systems to assay scintillator are presented

Adaptive Space Deformations Based on Rigid Cells

Botsch M, Pauly M, Wicke M, Gross M. Adaptive Space Deformations Based on Rigid Cells. Computer Graphics Forum. 2007;26(3):339-347