Sensor Tasking for Low Earth Orbit Objects: Leveraging Space Sensor Data for Ground-Based Optical Observations

Because of recent advancements in space technologies, easier and more economical access to space, and an increase in commercial interests, the near-Earth space environment has witnessed an exploding number of objects being put into orbit. In particular, the low Earth orbit (LEO) region is at an increased risk of orbital collisions from large satellite constellation projects. Thus, monitoring LEO objects for space situational awareness and space traffic management has become increasingly imperative. In this paper, we use the concept of limited-CDF (cumulative distribution function) surface and mutual information for designing sensor tasking algorithms focusing on regular observation of known catalog LEO objects (follow-up). Observations are carried out using a simulated ground-based optical telescope. The simulations are representative of realistic observation processes. We investigate how data from passive space-based sensors can be used to improve the follow-up performance of the telescope. A sensor-tasking framework is developed in which we conduct a comparative study to assess how different types of satellite constellation patterns such as Walker-delta and Walker-star affect the overall sensor tasking performance. Several case studies are carried out to address the following points: (1) what are the appropriate characteristics of the parameters to be optimized and how does it impact the evolution of orbital state uncertainties?, (2) compare different traditional and non-traditional algorithms for sensor tasking problem, (3) investigate the effect of measurements from different constellation configurations of passive space-based sensor, and (4) what is an appropriate coordinate system for the limited-CDF surface

Optimization of satellite constellation deployment strategy considering uncertain areas of interest

This paper presents an integrated framework to design a flexible multi-stage telecommunication satellite configuration deployment strategy considering the uncertainties in the evolution of the areas of interest over time. The constructed stochastic demand model considers multiple possible scenarios for the evolution of the areas of interest with probabilities based on the market share growth in each area. The optimization aims to find each stage’s design with minimum expected lifecycle cost considering all possible scenarios. Each stage of the constellation, assumed to be Flower constellation with circular orbits, provides a regional coverage of the current area of interest as well as additional coverage for the potential future areas of interest. The proposed multi-stage satellite constellation enables the constellation designer to react flexibly and efficiently to the uncertain future expansion of the areas of interest. A case study reveals a reduction in the expected lifecycle cost for an optimized system compared with the all-in-single-stage system and global coverage constellation

Design and Operations of Satellite Constellations for Complex Regional Coverage

Fueled by recent technological advancements in small and capable satellites, satellite constellations are now shaping the new era of space commercialization creating new forms of services that span from Earth observations to telecommunications and navigation. With the mission objectives becoming increasingly complex, a new paradigm in the design and operations of satellite constellations is necessary to make a system cheaper and more efficient. This dissertation presents a set of novel mathematical formulations and solution methods that lend themselves to various applications in the design and operations of satellite constellation systems. The second chapter establishes the Access-Pattern-Coverage (APC) decomposition model that relaxes the symmetry and homogeneity assumptions of the classical global-coverage constellation design methods. Based on the model, this dissertation formulates an integer linear programming (ILP) problem that designs an optimal constellation pattern for complex spatiotemporally-varying coverage requirements. The third chapter examines the problem of reconfiguring satellite constellations for efficient adaptive mission planning and presents a novel ILP formulation that combines constellation design and transfer problems that are otherwise considered independent and serial in the state-of-the-art. Furthermore, the third chapter proposes a Lagrangian relaxation-based heuristic method that exploits the assignment problem structure embedded in the integrated design-transfer model. The fourth chapter extends the third chapter by investigating the multi-stage satellite constellation reconfiguration problem and develops two heuristic sequential decision-making methods based on the concepts of myopic policy and the rolling horizon procedure. This dissertation presents several illustrative examples as proofs-of-concept to demonstrate the value of the proposed work.Ph.D

Satellite Constellation Pattern Optimization for Complex Regional Coverage

The use of regional coverage satellite constellations is on the rise, urging the need for an optimal constellation design method for complex regional coverage. Traditional constellations are often designed for continuous global coverage, and the few existing regional constellation design methods lead to suboptimal solutions for periodically time-varying or spatially-varying regional coverage requirements. This paper introduces a new general approach to design an optimal constellation pattern that satisfies such complex regional coverage requirements. To this end, the circular convolution nature of the repeating ground track orbit and common ground track constellation is formalized. This formulation enables a scalable constellation pattern analysis for multiple target areas and with multiple sub-constellations. The formalized circular convolution relationship is first used to derive a baseline constellation pattern design method with the conventional assumption of symmetry. Next, a novel method based on binary integer linear programming is developed, which aims to optimally design a constellation pattern with the minimum number of satellites. This binary integer linear programming method is shown to achieve optimal constellation patterns for general problem settings that the baseline method cannot achieve. Five illustrative examples are analyzed to demonstrate the value of the proposed new approach.Comment: 47 pages, 23 figures, Journal of Spacecraft and Rockets (Published

Cislunar Satellite Constellation Design Via Integer Linear Programming

Cislunar space awareness is of increasing interest to the international community as Earth-Moon traffic is projected to increase. This raises the problem of placing satellites optimally in a constellation to provide satisfactory coverage for said traffic. The Circular Restricted 3 Body Problem (CR3BP) provides promising periodic orbits in the Earth-Moon rotating frame for traffic monitoring. This work converts a spatially and temporally varying traffic coverage requirement into an integer linear programming problem, attempting to minimize the number of satellites required for the requested coverage.Comment: 18 pages, 15 figures, submitted to 2023 AAS Conferenc

The role of nafamostat mesilate as a regional anticoagulant during extracorporeal membrane oxygenation

Background Anticoagulation during extracorporeal membrane oxygenation (ECMO) usually is required to prevent thrombosis. The aim of this study was to investigate the usefulness of nafamostat mesilate (NM) as a regional anticoagulant during veno-arterial ECMO (VA-ECMO) treatment. Methods We retrospectively reviewed the medical records of 16 patients receiving VA-ECMO and NM from January 2017 to June 2020 at Haeundae Paik Hospital. We compared clinical and laboratory data, including activated partial thromboplastin time (aPTT), which was measured simultaneously in patients and the ECMO site, to estimate the efficacy of regional anticoagulation. Results The median patient age was 68.5 years, and 56.3% of patients were men. Cardiovascular disease was the most common primary disease (75.0%) requiring ECMO treatment, followed by respiratory disease (12.5%). The median duration of ECMO treatment was 7.5 days. Among 16 patients, seven were switched to NM after first using heparin as an anticoagulation agent, and nine received only NM. When comparing aPTT values in the NM group between patients and the ECMO site, that in patients was significantly lower than that at the ECMO site (73.57 vs. 79.25 seconds; P=0.010); in contrast, no difference was observed in the heparin group. Conclusions NM showed efficacy as a regional anticoagulation method by sustaining a lower aPTT value compared to that measured at the ECMO site. NM should be considered as a safer regional anticoagulation method in VA-ECMO for patients at high risk of bleeding

Ranitidine Use and Incident Cancer in a Multinational Cohort

Importance: Ranitidine, the most widely used histamine-2 receptor antagonist (H2RA), was withdrawn because of N-nitrosodimethylamine impurity in 2020. Given the worldwide exposure to this drug, the potential risk of cancer development associated with the intake of known carcinogens is an important epidemiological concern. Objective: To examine the comparative risk of cancer associated with the use of ranitidine vs other H2RAs. Design, Setting, and Participants: This new-user active comparator international network cohort study was conducted using 3 health claims and 9 electronic health record databases from the US, the United Kingdom, Germany, Spain, France, South Korea, and Taiwan. Large-scale propensity score (PS) matching was used to minimize confounding of the observed covariates with negative control outcomes. Empirical calibration was performed to account for unobserved confounding. All databases were mapped to a common data model. Database-specific estimates were combined using random-effects meta-analysis. Participants included individuals aged at least 20 years with no history of cancer who used H2RAs for more than 30 days from January 1986 to December 2020, with a 1-year washout period. Data were analyzed from April to September 2021. Exposure: The main exposure was use of ranitidine vs other H2RAs (famotidine, lafutidine, nizatidine, and roxatidine). Main Outcomes and Measures: The primary outcome was incidence of any cancer, except nonmelanoma skin cancer. Secondary outcomes included all cancer except thyroid cancer, 16 cancer subtypes, and all-cause mortality. Results: Among 1 183 999 individuals in 11 databases, 909 168 individuals (mean age, 56.1 years; 507 316 [55.8%] women) were identified as new users of ranitidine, and 274 831 individuals (mean age, 58.0 years; 145 935 [53.1%] women) were identified as new users of other H2RAs. Crude incidence rates of cancer were 14.30 events per 1000 person-years (PYs) in ranitidine users and 15.03 events per 1000 PYs among other H2RA users. After PS matching, cancer risk was similar in ranitidine compared with other H2RA users (incidence, 15.92 events per 1000 PYs vs 15.65 events per 1000 PYs; calibrated meta-analytic hazard ratio, 1.04; 95% CI, 0.97-1.12). No significant associations were found between ranitidine use and any secondary outcomes after calibration. Conclusions and Relevance: In this cohort study, ranitidine use was not associated with an increased risk of cancer compared with the use of other H2RAs. Further research is needed on the long-term association of ranitidine with cancer development.</p

The effects of direct hemoperfusion with polymyxin B-immobilized fiber in patients with acute exacerbation of interstitial lung disease

Background Acute exacerbation of interstitial lung disease (AE-ILD) causes clinically significant deterioration and has an extremely poor prognosis with high mortality. Recently, several studies reported the effectiveness of direct hemoperfusion with a polymyxin B-immobilized fiber column (PMX-DHP) in patients with AE-ILD as a potential therapy. This study describes the clinical effectiveness and safety of PMX-DHP in patients with AE-ILD. Methods We retrospectively reviewed the medical records of 10 patients (11 episodes) with AE-ILD treated with PMX-DHP from January 2018 to June 2019. We compared laboratory and physiologic data of the ratio of partial pressure arterial oxygen to fraction of inspired oxygen (P/F ratio) and level of inflammatory markers before and after implementation of PMX-DHP. Results Ten patients were included according to the 2016 revised definition of acute exacerbation of idiopathic pulmonary fibrosis (IPF). Nine patients had IPF and one patient had fibrotic nonspecific interstitial pneumonia. Most patients (90.9%) were treated with a steroid pulse, and four patients (36.4%) were treated with an immunosuppressant. The median number of PMX-DHP cycles was 2, and the median duration of each cycle was 6 hours. After PMX-DHP, the mean P/F ratio improved (86 [range, 63–106] vs. 145 [86–260], P=0.030) and interleukin-6 and c-reactive protein decreased (79 [35–640] vs. 10 [5–25], P=0.018 and 14 [4–21] vs. 5 [2–6], P=0.019, respectively). The 30-day mortality rate was 27.3% and the 90-day mortality rate was 72.7%. Conclusions PMX-DHP treatment improved P/F ratio and reduced inflammatory markers in AE-ILD patients

ITPKC Single Nucleotide Polymorphism Associated with the Kawasaki Disease in a Taiwanese Population

Kawasaki disease (KD) is characterized by systemic vasculitis with unknown etiology. Previous studies from Japan indicated that a gene polymorphism of ITPKC (rs28493229) is responsible for susceptibility to KD. We collected DNA samples from 1,531 Taiwanese subjects (341 KD patients and 1,190 controls) for genotyping ITPKC. In this study, no significant association was noted for the ITPKC polymorphism (rs28493229) between the controls and KD patients, although the CC genotype was overrepresented. We further combined our data with previously published case/control KD studies in the Taiwanese population and performed a meta-analysis. A significant association between rs28493229 and KD was found (Odds Ratio:1.36, 95% Confidence Interval 1.12–1.66). Importantly, a significant association was obtained between rs28493229 and KD patients with aneurysm formation (P = 0.001, under the recessive model). Taken together, our results indicated that C-allele of ITPKC SNP rs28493229 is associated with the susceptibility and aneurysm formation in KD patients in a Taiwanese population

Meta-analysis Followed by Replication Identifies Loci in or near CDKN1B, TET3, CD80, DRAM1, and ARID5B as Associated with Systemic Lupus Erythematosus in Asians

Systemic lupus erythematosus (SLE) is a prototype autoimmune disease with a strong genetic involvement and ethnic differences. Susceptibility genes identified so far only explain a small portion of the genetic heritability of SLE, suggesting that many more loci are yet to be uncovered for this disease. In this study, we performed a meta-analysis of genome-wide association studies on SLE in Chinese Han populations and followed up the findings by replication in four additional Asian cohorts with a total of 5,365 cases and 10,054 corresponding controls. We identified genetic variants in or near CDKN1B, TET3, CD80, DRAM1, and ARID5B as associated with the disease. These findings point to potential roles of cell-cycle regulation, autophagy, and DNA demethylation in SLE pathogenesis. For the region involving TET3 and that involving CDKN1B, multiple independent SNPs were identified, highlighting a phenomenon that might partially explain the missing heritability of complex diseases