ATTITUDE CONTROL OF MULTIPLE RIGID BODY SPACECRAFT WITH FLEXIBLE HINGE JOINTS

Control algorithm is developed for a satellite with flexible appendages to achieve a good pointing performance. Detailed modeling activity was carried out that consists of sensor and actuator models, disturbances and system dynamics. Common hardware found in the spacecraft such as reaction wheels, gyroscopes, star trackers etc. were included in the model. Furthermore, the Newton-Euler method is employed for the derivation of multi-body equations of motion. Proper metrics such as accuracy, jitter and stability are used to evaluate the pointing performance of two control schemes: quaternion feedback controller, and linear quadratic regulator. Simulation results are given and discussed

POINTING PERFORMANCE INVESTIGATION OF A MULTIPLE RIGID BODY SPACECRAFT

Earth Observation (EO) missions are characterized by high pointing performance. Also, spacecraft payloads are becoming more capable, demanding more power (and solar array area). This additional array area including its structural flexibilities has to be taken into account in the modeling of satellite dynamics, as well as disturbances and the components of attitude control system. A modeling task is undertaken to accurately represent the satellite and its components in the simulation environment. The pointing performance metrics are defined and implemented in the simulation loop as a part of this task. The effect of solar array configuration on the pointing performance is investigated

Radiological and anatomical evaluation of the posterior condylar canal, posterior condylar vein and occipital foramen*

Objectives:This study was carried out to make morphometric and radiological analyses of the occipital foramen (OF), posterior condylar canal (PCC), posterior condylar vein (PCV), and occipital emissary vein (OEV). Methods: Morphometric analyses were performed on 91 adult human occipital bones and radiological analyses on computed tomography (CT) angiography images of 221 patients. PCC length and mean diameters of the internal and externalorifices of PCC were measured and the number of OF on both sides was recorded for bony specimens. Prevalence of PCVand PCV size were investigated using CT angiography. Results: PCCs were observed in 60 bones (66%) on the left and 60 bones (66%) on the right side. Mean PCC length was10.85 ±3.41 and 9.77±3.55 on the left and right sides, consequently. Mean internal orifice diameter was 3.87±1.99 mm onthe left and 3.31±4.43 mm on the right side; mean external orifice diameter was 4.02±1.59 mm on the left and 3.89±1.52mm on the right side. The majority of PCCs (75%-81.6%) had 2-5 mm diameter; only 5-13.3% were small in size (<2mm).In CT angiography, PCV was not identified in 45(22.5%) patients. PCVs were located bilaterally in 114 (57%) and unilaterally in 41(20.5%) patients. Only 4.3% of PCVs (n=17) were large in size, the majority (27.5%) were medium-sized and35.8% small-sized. Conclusion:This study will contribute to the limited body of research on OF, PCC, PCV, and OEV as a guide to surgical interventions for pathologies of the posterior cranial fossa such as tumors and injuries.Objectives:This study was carried out to make morphometric and radiological analyses of the occipital foramen (OF), posterior condylar canal (PCC), posterior condylar vein (PCV), and occipital emissary vein (OEV). Methods: Morphometric analyses were performed on 91 adult human occipital bones and radiological analyses on computed tomography (CT) angiography images of 221 patients. PCC length and mean diameters of the internal and externalorifices of PCC were measured and the number of OF on both sides was recorded for bony specimens. Prevalence of PCVand PCV size were investigated using CT angiography. Results: PCCs were observed in 60 bones (66%) on the left and 60 bones (66%) on the right side. Mean PCC length was10.85 ±3.41 and 9.77±3.55 on the left and right sides, consequently. Mean internal orifice diameter was 3.87±1.99 mm onthe left and 3.31±4.43 mm on the right side; mean external orifice diameter was 4.02±1.59 mm on the left and 3.89±1.52mm on the right side. The majority of PCCs (75%-81.6%) had 2-5 mm diameter; only 5-13.3% were small in size (<2mm).In CT angiography, PCV was not identified in 45(22.5%) patients. PCVs were located bilaterally in 114 (57%) and unilaterally in 41(20.5%) patients. Only 4.3% of PCVs (n=17) were large in size, the majority (27.5%) were medium-sized and35.8% small-sized. Conclusion:This study will contribute to the limited body of research on OF, PCC, PCV, and OEV as a guide to surgical interventions for pathologies of the posterior cranial fossa such as tumors and injuries

TRAJECTORY TRACKING CONTROL OF AN UNDERACTUATED UNDERWATER VEHICLE REDUNDANT MANIPULATOR SYSTEM

The purpose of this study is to control the position of an underactuated underwater vehicle manipulator system (U-UVMS). It is possible to control the end-effector using a regular 6-DOF manipulator despite the undesired displacements of the underactuated vehicle within a certain range. However, in this study an 8-DOF redundant manipulator is used in order to increase the positioning accuracy of the end-effector. The redundancy is resolved according to the criterion of minimal vehicle and joint motions. The underactuated underwater vehicle redundant manipulator system is modeled including the hydrodynamic forces for the manipulator in addition to those for the autonomous underwater vehicle (AUV). The shadowing effects of the bodies on each other are also taken into account when computing the hydrodynamic forces. The Newton-Euler formulation is used to derive the system equations of motion including the thruster dynamics. In order to establish the endeffector trajectory tracking control of the system, an inverse dynamics control law is formulated. The effectiveness of the control law even in the presence of parameter uncertainties and disturbing ocean currents is illustrated by simulations