Structural design of booms for the solar sail of Helianthus sailcraft

Solar sail is a promising propulsion concept that exploits solar pressure to navigate in space without the use of propellants, therefore enabling missions otherwise not attainable by traditional propulsion (i.e. electric or chemical propulsion). For instance, a synchronous solar sail with the Earth-Moon barycenter to be used as a long warning time of solar storms caused by Coronal Mass Ejections is the main objective of the Helianthus project, funded by the Italian Space Agency. This paper is aimed specifically at the presentation and description of the design of the structural subsystem for the solar sail of the Helianthus project. This subsystem is composed of four deployable ultralight booms, which deploy and keep the sail-membrane in tension. The booms have to withstand the axial load, generated by the tensioned membrane, which must be smaller than the critical load at buckling. At the same time, the booms need to have sufficient stiffness to prevent a large out-of-plane displacement of the membrane leading to reduction of the thrust. First, the geometry and the dimensions of the boom cross-section to optimize the stiffness is determined. Then, a structural numerical analysis on a full-scale model of a square solar sail (40 m x 40 m) with four supporting booms is performed. For such configuration, the sail tension is simulated in order to determine the axial load acting on the tip of each boom and the displacements due to the solar radiation pressure are evaluated. Simulations are carried out by finite element method using the software ABAQUS. Results are presented at both system and individual components level

Effects of pre‐operative isolation on postoperative pulmonary complications after elective surgery: an international prospective cohort study

We aimed to determine the impact of pre-operative isolation on postoperative pulmonary complications after elective surgery during the global SARS-CoV-2 pandemic. We performed an international prospective cohort study including patients undergoing elective surgery in October 2020. Isolation was defined as the period before surgery during which patients did not leave their house or receive visitors from outside their household. The primary outcome was postoperative pulmonary complications, adjusted in multivariable models for measured confounders. Pre-defined sub-group analyses were performed for the primary outcome. A total of 96,454 patients from 114 countries were included and overall, 26,948 (27.9%) patients isolated before surgery. Postoperative pulmonary complications were recorded in 1947 (2.0%) patients of which 227 (11.7%) were associated with SARS-CoV-2 infection. Patients who isolated pre-operatively were older, had more respiratory comorbidities and were more commonly from areas of high SARS-CoV-2 incidence and high-income countries. Although the overall rates of postoperative pulmonary complications were similar in those that isolated and those that did not (2.1% vs 2.0%, respectively), isolation was associated with higher rates of postoperative pulmonary complications after adjustment (adjusted OR 1.20, 95%CI 1.05-1.36, p = 0.005). Sensitivity analyses revealed no further differences when patients were categorised by: pre-operative testing; use of COVID-19-free pathways; or community SARS-CoV-2 prevalence. The rate of postoperative pulmonary complications increased with periods of isolation longer than 3 days, with an OR (95%CI) at 4-7 days or >= 8 days of 1.25 (1.04-1.48), p = 0.015 and 1.31 (1.11-1.55), p = 0.001, respectively. Isolation before elective surgery might be associated with a small but clinically important increased risk of postoperative pulmonary complications. Longer periods of isolation showed no reduction in the risk of postoperative pulmonary complications. These findings have significant implications for global provision of elective surgical care