Controllability of an underactuated spacecraft with one thruster under disturbance

For an underactuated spacecraft using only one thruster, the attitude controllability with respect to the or- bit frame is studied in the presence of periodical oscillation disturbance, which provides a preconditional guide on de- signing control law for underactuated attitude control sys- tem. Firstly, attitude dynamic model was established for an underactuated spacecraft, and attitude motion was described using the special orthogonal group （SO （3））. Secondly, Liou- ville theorem was used to confirm that the flow generated by the drift vector of the underactuated attitude control system is volume-preserving. Furthermore, according to Poincar6＇s re- currence theorem, we draw conclusions that this drift field is weakly positively poisson stable （WPPS）. Thirdly, the suffi- cient and necessary condition of controllability was obtained on the basis of lie algebra rank condition （LARC）. Finally, the controllable conditions were analyzed and simulated in different cases of inertia matrix with the installed position of thruster.

Quality assessment of the practice of focused antenatal care (FANC) in rural and urban primary health centres in Ekiti State

Objective: To ascertain that standard antenatal care (Focused antenatal care) is being received at the Primary Health Care level in urban and rural areas of Ekiti State and to determine the facilitating factors and challenges to the practice of FANC in urban and rural areas. Design: Cross sectional. Setting: Primary Health Centers Participants: Pregnant women and Heads of health facilities. Methods: Two hundred respondents each from urban and rural areas primary health centres were proportionately selected from 18 primary health centers using simple random sampling. Exit interviews were conducted using the antenatal care exit interview form of the Safe Motherhood Needs Assessment package. In-depth Interviews were conducted with the heads of selected facilities. Data was analysed using descriptive statistics and Chi square test and content analysis for indepth interview. Results: More respondents 58 (29.3%) from the urban areas had the minimum contents compared to 41 (20.7%) of the rural respondents (p < 0.05) and 178 (90.8%) of the urban were taught a range of health education topics compared to 177 (88.5%) (p = 0.45). Urban respondents were about 1.6 times more likely to receive the minimum contents than rural respondents. In-depth interview results explicated the facilitating factors and challenges to focused antenatal care in the study areas. Conclusion: The findings of this study is consistent with other studies establishing the fact that better health service is available to urban residents than rural residents;however, this study has succeeded in comparing the documented standard of antenatal care with what was being practiced in the selected PHCs of the state. The basic contents of focused antenatal care in Ekiti state were received by a small proportion of the respondents, suggesting that focused antenatal care had not fully translated into quality service;one major challenge to the delivery of standard antenatal care was inadequate number of skilled health workers especially in the rural areas. The gap between quality and utilisation of antenatal in urban and rural areas is gradually being closed up;this success should be improved upon and maintained.

Psychosocial Determinants of Postpartum Depression and Maternal Well-Being among Postnatal Women

Postpartum depression, a major depressive disorder, predisposes postnatal mothers to physical, social, and psychological malfunctioning. Purpose: The study aimed to identify the psychosocial determinants of postpartum depression and maternal well-being among mothers in the Accra metropolis. Materials and Method: A sample of 205 postnatal women between the ages of 15 - 39 years and are 4 - 12 weeks old postpartum was drawn from 37 Military Hospital, Accra. Employing a sequential explanatory approach, participants were administered the Depression, Anxiety and Stress Scale (DASS-21), Multidimensional Scale of Perceived Social Support (MSPSS), Marital Adjustment Test (MAT), and the Edinburgh Postnatal Depression Scale (EPDS). Findings: The study revealed that 14.1% of postnatal women in the Accra metropolis are at risk of developing PPD. A significant model emerged, [R2 = 0.488, F (7, 197) = 26.86, ρ < 0.05] and this was predicted by anxiety, stress and marital dissatisfaction among couples. On the other hand, results from Interpretive Phenomenological Analysis (IPA) of participants’ in-depth information revealed inadequate social support and dissatisfaction in marriage account for mothers’ at-risk behaviour of developing PPD;which impacts on maternal well-being. Conclusion: It is concluded that PPD is patent among postnatal women and psychosocial variables contribute a significant role in their experience of mental health problems following childbirth. This, in effect, requires attention from health professionals for holistic healthcare. The implications of these outcomes are discussed concerning mental healthcare delivery, the general public, and stakeholders in the health sector.

Underactuated spacecraft angular velocity stabilization and three-axis attitude stabilization using two single gimbal control moment gyros

Angular velocity stabilization control and attitude stabilization control for an underactuated spacecraft using only two single gimbal control moment gyros （SGCMGs） as actuators is investigated. First of all, the dynamic model of the underactuated spacecraft is established and the singularity of different configurations with the two SGCMGs is analyzed. Under the assumption that the gimbal axes of the two SGCMGs are installed in any direction, and that the total system angular momentum is not zero, a state feedback control law via Lyapunov method is designed to globally asymptotically stabilize the angular velocity of spacecraft. Under the assumption that the gimbal axes of the two SGCMGs are coaxially installed along anyone of the three principal axes of spacecraft inertia, and that the total system angular momentum is zero, a discontinuous state feedback control law is designed to stabilize three-axis attitude of spacecraft with respect to the inertial frame. Furthermore, the singularity escape of SGCMGs for the above two control problems is also studied. Simulation results demonstrate the validity of the control laws.

Control of orientation for spacecraft formations in the vicinity of the Sun-Earth L2 libration point

Formation flying in the vicinity of the libration point is an important concept for space exploration and demands reliable and accurate techniques for the control of a spacecraft.On the basis of previous works,this paper addresses the problem of relative orientation control of spacecraft formation flying utilizing the framework of the circular restricted three-body problem(CR3BP)with the Sun and Earth as the primary gravitational bodies.Two specific tasks are accomplished in this study.First,the tangent targeting method(TTM),an efficient two-level differential correction algorithm,is exploited to control the Chief/Deputy architecture to maintain a prespecified orientation.The time spent within the orientation error corridor between successive maneuvers is maximized while the relative separation between the vehicles is held constant at each target point.The second task is to further optimize the maneuver intervals by dropping the constraint imposed on the relative vehicle separation.Numerical investigation indicates that the number of maneuvers can be significantly reduced and the length of time between successive maneuvers can be greatly increased by utilizing the TTM.