3,341 research outputs found
A new momentum management controller for the space station
A new approach to CMG (control moment gyro) momentum management and attitude control of the Space Station is developed. The control algorithm utilizes both the gravity-gradient and gyroscopic torques to seek torque equilibrium attitude in the presence of secular and cyclic disturbances. Depending upon mission requirements, either pitch attitude or pitch-axis CMG momentum can be held constant: yaw attitude and roll-axis CMG momentum can be held constant, while roll attitude and yaw-axis CMG momentum cannot be held constant. As a result, the overall attitude and CMG momentum oscillations caused by cyclic aero-dynamic disturbances are minimized. A state feedback controller with minimal computer storage requirement for gain scheduling is also developed. The overall closed-loop system is stable for + or - 30 percent inertia matrix variations and has more than + or - 10 dB and 45 deg stability margins in each loop
Designing conjugated porous polymers for visible light-driven photocatalytic chemical transformations
Modeling, system identification, and control of ASTREX
The modeling, system identification and controller design aspects of the ASTREX precision space structure are presented in this work. Modeling of ASTREX is performed using NASTRAN, TREETOPS and I-DEAS. The models generated range from simple linear time-invariant models to nonlinear models used for large angle simulations. Identification in both the time and frequency domains are presented. The experimental set up and the results from the identification experiments are included. Finally, controller design for ASTREX is presented. Simulation results using this optimal controller demonstrate the controller performance. Finally the future directions and plans for the facility are addressed
Demonstration of nanoimprinted hyperlens array for high-throughput sub-diffraction imaging
11124Nsciescopu
THE CONTRIBUTION OF LOWER TORSO, UPPER TORSO AND UPPER LIMBS SEGMENTAL MOTION TO HAMMER HEAD VELOCITY DURING ACCELERATION PHASE
In hammer throw event, the distance of the hammer throw is mainly determined by hammer head resultant velocity at release. During turn phase, hammer head resultant velocity is increased gradually with four turns and is increased during double support phase. The purpose of this study was to investigate the contribution of the motions in the lower torso, upper torso, upper limbs and hammer segment to the hammer head tangential velocity during double support phase
Optical observations of NEA 162173 (1999 JU3) during the 2011-2012 apparition
Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid
sample return missions, not only because of its accessibility but also because
of the first C-type asteroid for exploration missions. The lightcurve-related
physical properties of this object were investigated during the 2011-2012
apparition. We aim to confirm the physical parameters useful for JAXA's
Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase
function. Our data complement previous studies that did not cover low phase
angles. With optical imagers and 1-2 m class telescopes, we acquired the
photometric data at different phase angles. We independently derived the
rotational lightcurve and the phase curve of the asteroid. We have analyzed the
lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of
7.625 +/- 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R =
18.69 +/- 0.07 mag and the phase slope of G = -0.09 +/- 0.03 were also obtained
based on the observations made during the 2011-2012 apparition.Comment: 4 pages, 3 figure
- …