Mirror formation control in the vicinity of an asteroid

Two strategies are presented for the positioning and control of a spacecraft formation designed to focus sunlight onto a point on the surface of asteroid, thereby sublimating the material and ejecting debris creating thrust. In the first approach, the formation is located at artficial equilibrium points around the asteroid and controlled using the force from the solar radiation pressure. The second approach determines the optimal periodic formation orbits, subject to the gravitational perturbations from the asteroid, the solar radiation pressure and the control acceleration derived from a control law

On the deflection of asteroids with mirrors

This paper presents an analysis of an asteroid deflection method based on multiple solar concentrators. A model of the deflection through the sublimation of the surface material of an asteroid is presented, with simulation results showing the achievable orbital deflection with, and without, accounting for the effects of mirror contamination due to the ejected debris plume. A second model with simulation results is presented analyzing an enhancement of the Yarkovsky effect, which provides a significant deflection even when the surface temperature is not high enough to sublimate. Finally the dynamical model of solar concentrators in the proximity of an irregular celestial body are discussed, together with a Lyapunov-based controller to maintain the spacecraft concentrators at a required distance from the asteroid

Can childbirth be changed? - offering women a choice

This article discusses the implementation and evaluation of an initiative to routinely provide healthy women with five choices for the type of maternity care they receive (community- and hospital-based shared care, named midwife care, DOMINO and home birth). A cohort study of 345 women was carried out at the Glasgow Royal Maternity Hospital. The study aimed to: determine the proportion of women offered choice for their type of maternity care after the introduction of the initiative; determine the proportion of women choosing the different types of care and to examine the socio-demographic predictors of the choice of care; and examine women's attitudes to being offered a choice in the type of maternity care they receive and reasons for making particular choices. The study was carried out using a retrospective review of case records and self-report questionnaires from a consecutive sub-sample of 170 women. Of those eligible, 90% (95% CI: 86% to 93%) were offered choice of care type. Half of the eligible women chose community-based shared care, 36% chose named midwife care, 10% chose hospital-based shared care, 4% requested DOMINO care and less than 1% selected home birth. Women's choice of the type of care they received was unrelated to their socio-demographic characteristics. Women were satisfied with the way that choices were offered and valued being able to choose their type of care. The response rate of the questionnaire was 84%. This article concludes that it may be realistic to routinely offer women a variety of choices of the care type they receive given the support of the professional groups involved. </jats:p