Shooting method to allow for perturbations in the optimized boundary value initial orbit determination

Space debris poses threats to functional spacecraft around the Earth due to the possibility of collisions in orbit. The debris object population needs to be cataloged to monitor the space environment. Optical surveys result in observations of objects on very short arcs (when compared to their orbital period). These short-arc angles-only observations are not suitable to derive a reliable orbit, hence two of them are associated together to test if they belong to the same object and to compute initial orbits. Initial Orbit determination (IOD) is done using the Optimized Boundary Value Initial Orbit Determination (OBVIOD), which is an existing method to associate short-arc optical observations. A so-called shooting method is used inside the OBVIOD to include perturbations. This method consists of choosing a hypothetical value for a variable at first boundary and propagating to the second boundary. The propagation from one boundary to the second includes perturbations such as solar radiation pressure, earth’s geopotential terms, solar and lunar gravitational forces. The root-finding method used inside the Shooting procedure may take its initial value from the unperturbed solution. However, root-finding methods, like e.g. Newton-Raphson, might have difficulties in the convergence or converge to a wrong solution in case the initial value lies far from the actual root. In addition, for multiple revolutions scenarios several possible solutions, according to the high and low path of the Lambert problem, have to be computed inside the OBVIOD. A root-finding method based on bisection is proposed to get global convergence. Constraints originating from an admissible region approach are set to narrow down the possible scenarios, which are be computed to find the desired solutions. Both, the proposed method and Newton-Raphson are tested for their performance inside the Shooting-OBVIOD. Tests are done using simulated short-arc angles-only observations, separated by single or multiple revolutions, and different area-to-mass ratio values for the observed objects. The results lead to the conclusion that the proposed method is superior to the previous one for use inside OBVIOD to associate short-arc optical observations

Perturbations in the optimized boundary value initial orbit determination approach

One of the increasing threats to functional spacecraft around Earth is that of Space Debris. The risks that it poses for current and future space operations due to collisions are growing in an exponential manner. It is essential to create and maintain a catalog of space debris to monitor the space environment. Optical survey observations from the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald, Switzerland, are used to discover space debris objects. The result of these surveys are observations of objects on very short arcs (when compared to their orbital period). Optimized Boundary Value Initial Orbit Determination (OBVIOD) is one existing method to associate short-arc observations with each other and to compute initial orbits. This method is based on the solution of the Lambert problem. An important extension of this initial orbit determination method consists in including perturbations. One way to accomplish this task is by using shooting methods. In the methods hypothetical initial values are chosen at one boundary and, after integration up to the second boundary, the end values are compared with the boundary conditions. The hypothetical values satisfying the boundary conditions are accepted as the solution of the problem. We also analyzed to what extent the Keplerian model gives acceptable results and under what conditions it becomes imperative to include perturbations in the model. This was done by comparing the performance of this initial orbit determination algorithm with and without the addition of perturbations. Here performance refers to the capability of correlating the short-arc observations, which truly belong to the same object. Moreover, the analysis of different factors including computational complexity, the time taken for the algorithm to converge was also done. The tests include simulated observations for the GEO orbital regime. These observations were simulated using the same perturbation model as in the initial orbit determination. Later tests were performed using real observations obtained from the optical surveys of the Zimmerwald Observatory

Space debris observations with the Slovak AGO70telescope: Astrometry and light curves

The Faculty of Mathematics, Physics and Informatics of Comenius University in Bratislava, Slovakia (FMPI) operates its own 0.7-m Newtonian telescope (AGO70) dedicated to the space surveillance tracking and research, with an emphasis on space debris. The observation planning focuses on objects on geosynchronous (GEO), eccentric (GTO and Molniya) and global navigation satellite system (GNSS) orbits. To verify the system’s capabilities, we conducted an observation campaign in 2017, 2018 and 2019 focused on astrometric and photometric measurements. In last two years we have built up a light curve catalogue of space debris which is now freely available for the scientific community. We report periodic signals extracted from more than 285 light curves of 226 individual objects. We constructed phase diagrams for 153 light curves for which we obtained apparent amplitudes

Hypoxemic Respiratory Failure and Coccidioidomycosis-Associated Acute Respiratory Distress Syndrome

BackgroundSevere coccidioidomycosis presenting with respiratory failure is an uncommon manifestation of disease. Current knowledge of this condition is limited to case reports and small case series.MethodsA retrospective multicenter review of patients with coccidioidomycosis-associated acute respiratory distress syndrome (CA-ARDS) was conducted. It assessed clinical and laboratory variables at the time of presentation, reviewed the treatment course, and compared this cohort with a national database of patients with noncoccidioidomycosis ARDS. Survivors and nonsurvivors of coccidioidomycosis were also compared to determine prognostic factors.ResultsIn this study, CA-ARDS (n = 54) was most common in males, those of Hispanic ethnicity, and those with concurrent diabetes mellitus. As compared with the PETAL network database (Prevention and Early Treatment of Acute Lung Injury; n = 1006), patients with coccidioidomycosis were younger, had fewer comorbid conditions, and were less acidemic. The 90-day mortality was 15.4% for patients with coccidioidomycosis, as opposed to 42.6% (P < .0001) for patients with noncoccidioidomycosis ARDS. Patients with coccidioidomycosis who died, as compared with those who survived, were older, had higher APACHE II scores (Acute Physiology and Chronic Health Evaluation), and did not receive corticosteroid therapy.ConclusionsCA-ARDS is an uncommon but morbid manifestation of infection. When compared with a national database, the overall mortality appears favorable vs other causes of ARDS. Patients with CA-ARDS had a low overall mortality but required prolonged antifungal therapy. The utility of corticosteroids in this condition remains unconfirmed

Slovakian Optical Sensor for HAMR Objects Cataloguing and Research

Slovakia became the 9th ESA European Cooperative State in 2015 and the first calls to action for the Plan for European Cooperating State (PECS) were announced shortly after. The Department of Astronomy and Astrophysics, a part of the Faculty of Mathematics, Physics and Informatics of Comenius University in Bratislava, Slovakia (FMPI CU), won the call and an activity with a main goal to transform a 0.7-m Newton telescope (AGO70) dedicated to amateur astronomical observations to a professional optical system for regular support of the space debris tracking and research has started. The transformation includes the necessary hardware and software modifications to the existing solution. The presented activity has been performed in cooperation with the Astronomical Institute of University of Bern (AIUB). The AGO70 has been installed at the FMPI's Astronomical and Geophysical Observatory in Modra, Slovakia (AGO) in fall 2016. There are several predefined objectives to be accomplished within the activity. First, it was imperative to adapt the low-level telescope control for the needs of space debris tracking. Second, the image processing software must have been developed in a modular way. The observation planning has been formulated according to the AGO70 system's hardware limitations with focus on GEO, GTO and GNSS like orbits. To verify the system's capabilities, the whole activity is concluded with an observation campaign measuring AIUB's HAMR (High-Area-to-Mass-Ratio) objects and public TLE objects. The quality of the system's output is monitored by the AIUB via its state-of-the-art epoch bias and astrometric accuracy analysis routines