Attitude Disturbance Research Articles

Path Planning of Space Manipulators to Reduce Spacecraft Attitude Disturbances.

Motions of a space manipulator cause dynamic disturbances to the spacecraft attitude. This paper proposes a method of path planning for space manipulators to reduce such dynamic disturbances. The method is based on the concept of the Enhanced Disturbance Map where the direction of joint movements that causes zero disturbance to the spacecraft attitude is given in the joint space. In this paper, this approach is applied to the path planning of space manipulators. The proposed method determines the direction of small joint movements at each step that causes zero atteitude disturbance and moves the end effector toward a desired position. The path planning algorithms are presented first for the case of non-redundandant DOF space manipulators and, then, for redundant DOF space manipulators. The present method also avoids the singular points in the joint space by means of the singularity low-sensitive motion resolution method. Results of numerical simulations are presented for a two-link planner space manipulator system and for a three-link redundant system.

Path Planning for Space Manipulators to Reduce Attitude Disturbances

Path Planning for Space Manipulators to Reduce Attitude Disturbances

Patterns of personality disorder comorbidity in early-onset versus late- onset major depression

This study tested the hypothesis that in a population of adult outpatients with major depression, those with an early onset of depression would have a greater prevalence of personality disorders than those with a late onset of depression. The 404 subjects were patients participating in depression treatment studies at the Massachusetts General Hospital. They were administered the Structured Clinical Interview for DSM-III-R-Patient Version to assess the current presence of major depression and the age at onset of the initial depressive episode. The subjects were then divided into two groups: those with early onset (before 18 years of age) and those with late onset (at age 18 or later). The prevalence of personality disorders was determined through use of the physician-rated Structured Clinical Interview for DSM-III-R Personality Disorders (SCID-II) and the patient-rated Personality Diagnostic Questionnaire-Revised (PDQ-R). The patients with early onset of major depression had a significantly higher prevalence of avoidant, histrionic, narcissistic, and borderline personality disorders according to the SCID-II. The PDQ-R scores indicated that avoidant, dependent, passive-aggressive, histrionic, narcissistic, borderline, and antisocial personality disorders were significantly more prevalent among the patients with early onset of major depression. Overall, the results are consistent with the view that early-onset depressive illness is distinguished from late-onset major depression by more frequent association with persistent disturbances in behaviors and attitudes.

Solar pressure disturbance on GSTAR and SPACENET satellites

In the geosynchronous orbit, the solar pressure is the primary source of environmental attitude disturbance on the GSTAR and SPACENET satellites. These disturbances are countered by the momentum wheel for the pitch torque, and by the magnetic torquers for the roll and yaw torque. In addition, the north and south solar arrays are differentially slewed to provide an inertially fixed torque to augment the magnetic torquers. This paper attempts to estimate the actual solar pressure torque on the GSTAR I and the SPACENET I satellites at different times of the year. This is obtained by analyzing the on-orbit performance of the momentum wheels and the duty cycles of the magnetic torquers. This paper serves two purposes. Firstly, it estimates the actual solar disturbance torque on satellites in geosynchronous orbit, thereby providing empirical data that can be used for satellite operations. Typically, this information can be used for optimally scheduling some stationkeeping maneuvers, as well as for using solar arrays to augment attitude control operations. Secondly, this data can be used by the designers/manufacturers of satellites to validate then* solar pressure disturbance models that are used to design the attitude control system.

Minimizing spacecraft attitude disturbances in space manipulator systems

This paper presents a technique called the enhanced disturbance map to plan space manipulator motions that will result in relatively low spacecraft disturbances. This subject is of significant concern because future robotic systems used in space may encounter problems due to the dynamic disturbances imposed on their spacecraft by their manipulator motions. Although a spacecraft's attitude control reaction jets can compensate for these dynamic disturbances, jet fuel is a limited resource and excessive disturbances would limit the life of a system. The enhanced disturbance map can aid in understanding this complex problem and in the development of algorithms to reduce disturbances, including ones that use manipulator redundancy to eliminate the disturbances.

Analysis of a redundant free-flying spacecraft/manipulator system

An analysis of the momentum conservation equations of a redundant free-flying spacecraft/manipulator system acting in a zero-gravity environment is presented. In order to follow a predefined end-effector path, the inverse kinematics at velocity level is considered. The redundancy is solved alternatively in terms of pseudoinverses and null-space components of the manipulator inertia matrix, the manipulator Jacobian matrix, and the generalized Jacobian matrix. A general manipulation task is defined as end-effector continuous path tracking with simultaneous attitude control of the spacecraft. Three subtasks of the general task are considered. The case of manipulator motions that yield no spacecraft attitude disturbance is analyzed in more detail and a special 'fixed-attitude-restricted' (FAR) Jacobian is defined. Through singular-value decomposition of this Jacobian, corresponding FAR dexterity measures (FAR manipulability and FAR condition number) are derived. >

A novel autonomous orbit determination system using Earth sensors (scanner)

With a pair of conical Earth scanners operating as attitude sensors, four horizon points are obtained during each scan. Using three of the four points, a unique method is derived to obtain the distance and direction of the Earth's centre with respect to the satellite position. The fourth point, used in a least squares or averaging manner, improves accuracy. Combining this data with on-board 3-axis attitude, it is shown that a position accuracy of better than 4 km could be achieved. A simple digital low pass filter incorporated in the measurement path improves the accuracy to better than 2 km, and also improves the transient response of the Kalman filter during sudden attitude disturbances due to panel rotations. A simple state prediction (position, velocity vectors) based on f, g series makes the state dynamics linear without deteriorating the performance. The average behaviour of the errors are based on 20 simulation runs.

Solar Sailing Attitude Control of Large Geostationary Satellite

On geostationary satellite, the main source of attitude disturbance during normal mode Is the solar pressure effect on the body, the antennas and the solar arrays. In presence of these disturbances it is necessary, in a momentum biased control system, to maintain the momentum direction perpendicular to the orbit plane (roll/yaw control); as it has been demonstrated in orbit on OTS2, the solar pressure can be used to maintain this orientation. The originality of the proposed design consists in the use of two fixed sails mounted on the solar arrays to improve the control efficiency. The disturbing torques can be estimated on ground and compensated by command on the solar arrays pointing angle. The residual part of the disturbances as well as the nutation motion are controlled in closed loop. The control torques are achieved by low depolnting oi the solar arrays. These depointing angles are on-board computed by a microprocessor using a simplified model of the solar pressure effect on the sails. The total required depointing of the solar arrays limits their efficiency loss to 1%. After a brief description of the geostationary spacecraft environment, the solar pressure effect on the sails as also the solar sailing control laws arc precisely described in the paper. A summary of the performances is presented including the pointing accuracy. As a conclusion, the improvement due to the proposed solar sailing design is recalled and growth capacity is briefly indicated.

Dust environment models for comet P/Halley: Support for targeting of the GIOTTO S/C

In March 1985 ESA's GIOTTO spacecraft will fly by P/Halley's nucleus at a distance of a few hundred kilometres. The near nucleus dust environment the probe will traverse poses a hazard with respect to physical damage as well as to attitude disturbance with the possible loss of ground station contact. To predict S/C survivability and dust impact rates for the experiments, a model of the spatial distribution of the dust in the nucleus' vicinity is required. In the ‘dynamic’ model, the local spatial dust density is derived from exact expressions for the dust particle dynamic motion. The model has been implemented in a software system which allows for fast simulations of a cometary fly-by.

Mothers' psychological reactions to premature and full-size newborns.

PARENTAL attitudes are important influences in the development of a child's personality. 1 Disturbances in the early attitudes of mothers to their newborns may lead to chronic disturbances in the motherchild relationship. 2 Since some of the psychological disturbances associated with prematurity may in themselves be the result of impaired mother-child relations, 3 it would seem fruitful to explore the differences in psychological reaction patterns between mothers of premature and full-size infants during the early postpartum period to help clarify these issues. Bibring describes pregnancy as maturational crisis which, when successfully mastered, allows the woman to accept her new role as a mother. 2 Bibring states that the initial psychological task of the pregnant woman is to accept the growing fetus not as a foreign body but as part of herself. Bibring further states that with quickening a new phase starts

An Analysis of Pilot Adaptation in a Simulated Multiloop VTOL Hovering Task

Human pilot adaptation in a simulated multiloop VTOL hovering task was investigated with a series-loop-closure model. Using the model equations, the pilot-model adaptable parameters were computed from rms hovering performance data measured in flight simulator experiments for a variety of VTOL aircraft configurations. Variations in the aircraft configurations affected both the aircraft's dynamic characteristics and its response to simulated turbulence. The pilot's pitch-loop adaptation generally correlated with the frequency-domain characteristics of the pitch response to turbulence and the pitch response to control inputs. The results of the study show no specific low-frequency attitude gain requirements that must be satisfied by the pilot for the attitude disturbance and dynamic characteristics considered. The influence of the aircraft position-loop characteristics on pilot pitch-loop adaptation was important only for configurations that had small attitude disturbances. For these cases the requirements for position-loop control apparently determined the minimum acceptable pitch-loop crossover frequency. Results also show that the pilot preferred to adjust pitch-loop gain by changing control-stick sensitivity (aircraft gain) rather than by changing his internal gain.

Attitude perturbation of space vehicles by meteoroid impacts.

A procedure for calculating the attitude disturbances imparted to a spacecraft by the impacts of meteoroids is presented herein. It is shown that the anisotropy of the incident flux of meteoroids on the space vehicle, coupled with the inherent asymmetry of typical vehicles, leads to a steady-state disturbance in addition to the possibility of disturbance torques due to single impacts of relatively rare, large particles. It is further shown that a multiplication of momentum effect takes place during the hypervelocity impact of a meteoroid; this phenomenon can increase the attitude perturbation effect of meteoroids by an order of magnitude. Finally, it is illustrated that, in spite of uncertainties of several orders of magnitude in the results, it is possible to accommodate the most pessimistic situation without excessive weight penalties and without undue complexity in the design of an attitude control system.