Contactless attitude control of an uncooperative satellite by laser ablation

An active debris removal method using a laser is a promising technology for its advantage in contactless operations. This paper deals with the attitude control of an uncooperative target by a laser, which is an important phase before deorbiting. The difficulty of attitude control by the laser stems from the torque directional constraint because the laser generates thrust along the normal vector of the irradiated face irrespective of the irradiating direction. Thus, the control torque along the normal vector cannot be generated, which makes the attitude control with the laser torque challenging. To tackle this problem, this paper first designs a reference controller that assumes arbitrary control torques are available. Then, a method for determining the irradiating point is proposed so that the difference between the reference torque and the actual one is minimized. Although the proposed controller does not guarantee theoretical convergence to the desired attitude, the effectiveness of the proposed controller is numerically verified for a box-type object. Furthermore, the robustness to the uncertainties of thrust magnitude and direction is also examined by Monte Carlo simulations.Published version is available for viewing only. (See "Related URI")「関連URI」より出版社版の閲覧専用ページへリン

Risk Assessment of a Large Constellation of Satellites in Low-Earth Orbit

This paper aims to assess the risk of mission termination for a large constellation of satellites in a low-Earth orbit. Many large constellations will be deployed to provide broadband network services using thousands of satellites. There is concern that such large constellations will have a serious impact on the long-term sustainability of outer space activities due to the rapid increase in population. First, therefore, the authors conducted an assessment under nominal activities (referred to as “business-as-usual”) on the basis of a prediction by ESA’s MASTER-2009 and NASA standard breakup model 2001 revision. The assessment found that nearly one catastrophic collision may happen in a large constellation, generating more than two million fragments as small as 1mm in size. Second, the authors conducted a further assessment assuming a hypothetical collision of a satellite in a large constellation using the NASA standard breakup model and a spherical finite element model adopted in ESA’s MASTER-2009. In consequence, another catastrophic collision may happen to a large constellation, generating approximately a half-million fragments as small as 1mm in size. Therefore, such catastrophic collisions and resulting secondary collisions should be prevented for large constellations

Posterior reversible encephalopathy syndrome (PRES) associated with SARS-CoV-2 infection in a patient under maintenance haemodialysis: a case report

Abstract Background Endothelial dysfunction is common in patients undergoing chronic haemodialysis, and is a major cause of posterior reversible encephalopathy syndrome (PRES). Recently, Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been shown to cause endothelial dysfunction by infecting vascular endothelial cells. Several cases of neurological complications in patients without kidney dysfunction, and only a few cases in patients with chronic kidney disease, have been reported in the literature. However, no previous report has yet described PRES associated with SARS-CoV-2 infection among patients undergoing maintenance dialysis. Case presentation A 54-year-old woman undergoing maintenance haemodialysis was admitted to our hospital for status epilepticus. She had developed end-stage kidney disease (ESKD) secondary to diabetic nephropathy. Seven days prior to admission, she had developed fever and was diagnosed with COVID-19. Subsequently her blood pressure increased from 160/90 mmHg to 190/100 mmHg. On admission, she presented with severe hypertension (> 220/150 mmHg), unconsciousness, and epilepticus. CT tomography revealed no signs of brain haemorrhage. Cranio-spinal fluid (CSF) examination revealed no signs of encephalitis, and CSF polymerase chain reaction (PCR) for SARS-CoV-2 was negative. MRI findings revealed focal T2/FLAIR hyperintensity in the bilateral parietooccipital regions, leading to the diagnosis of PRES. Deep sedation and strict blood pressure control resulted in a rapid improvement of her symptoms, and she was discharged without sequelae. Conclusions We report the first case of PRES associated with SARS-CoV-2 infection in a patient undergoing maintenance haemodialysis. Patients undergoing maintenance haemodialysis are at high risk of PRES because of several risk factors. SARS-CoV-2 infection causes direct invasion of endothelial cells by binding to angiotensin-converting enzyme 2 (ACE2), initiating cytokine release, and hypercoagulation, leading to vascular endothelial cell injury and increased vascular leakage. In the present case, SARS-CoV-2 infection possibly be associated with the development of PRES