Search Results (7)

For the mission requirements of the preliminary design phase for kinetic impact deflection of asteroids, an improved pork-chop plot design method is proposed which comprehensively considers both engineering constraints and deflection effectiveness. This method enables the visualization of engineering constraints, such as launch site, launch vehicle, and impact visibility, as well as the deflection distance after impact, all within a single plot. It provides a set of initial values that meet the requirements within the designated window for subsequent trajectory correction, based on different mission needs. Based on the patched conic technique, this paper first establishes a dynamical model for the spacecraft’s trajectory to the asteroid and then determines the parameters for both Earth departure and asteroid impact by solving the Lambert problem. Then, based on the departure parameters, the expression for Earth parking orbit escape is derived, and the constraints of rocket coasting time and launch site latitude, respectively, are transformed into parameter constraints on the argument of perigee and launch declination. Based on the impact parameters, an asteroid deflection dynamics model is established to compute the asteroid’s apparent magnitude and deflection distance. Finally, the improved pork-chop plot is generated using the aforementioned models. The plot comprehensively displays the optimized target parameters and engineering constraint parameters throughout the entire process, from launch vehicle departure to the post-impact deflection distance, within the given launch window. This provides initial values that satisfy both engineering constraints and mission requirements for the trajectory design of an in-orbit kinetic impactor asteroid deflection test mission. Compared to other trajectory design methods that provide only a single trajectory, the improved pork-chop plot enables a rapid, intuitive, and comprehensive visualization of a cluster of launch trajectories within the feasible window that satisfy engineering constraints. This approach reduces the number of iterations required for matching the deep-space transfer trajectory with the launch vehicle injection phase from more than five to one. The proposed method can serve as a valuable reference for target selection and trajectory optimization in in-orbit validation missions for kinetic impact deflection of asteroids. Full article

For the convenience of comparison with previous literature, the gravity calculations are revisited for the Asteroid 4769 Castalia, but with extensions on its surface and on intersecting planes and spheres around it, using the polyhedron and harmonic expansion methods with different order and degree for different cases, especially including the gravitational accelerations inside the asteroid, which did not appear at all before. In these evaluations, a few different facts of the these methods and results are revealed, such as the fact that gravity diverges when the position radius is less than the mean radius from harmonic-expansion method, and the maximum gravity is not at the deep valley and mountain top. For a surface that intersects the asteroid, the maximum gravity on it is at the intersection lines between the asteroid surface and the spheres or planes. This means that on the sphere and the plane, the gravities inside and outside the asteroid are smaller than the gravity on the intersection, i.e., on the surface. Some analyses of these conclusions are given with many examples with different radii of the sphere and with different order and degree harmonic expansion models for the above asteroid surface and surrounding spheres. It is interesting to note that very few researchers know that the polyhedral method can also be used to calculate the gravity inside an asteroid with just some modifications of the code. Some special gravity figures on surface and planes inside the asteroid Castalia are computed and made for the first time. The calculations also include tangential gravity, potential, and gravitational slope on surface. Specifically, we find that the overall mean gravitational slope could be one kind of indicator of the density of an asteroid. The minimum overall mean slope happens when the asteroid density is about 2.9 g/cm³, which is much larger than a usually assumed value between 1.7 and 2.5 for asteroid Castalia when its period is 4.07 h, since rotation period should be a more accurate parameter than its estimated density. These conclusions about this typical prolate-like asteroid could be a benchmark for analyzing other similar asteroids. Full article

Purpose: To describe the appearance of vitreous opacities using dynamic ultra-widefield infrared confocal scanning laser ophthalmoscopy (IRcSLO). Design: Retrospective case series. Methods: Eyes of patients complaining of myodesopsia were analyzed using dynamic ultra-widefield IRcSLO imaging (Nidek Mirante, Nidek Co., Ltd., Gamagori, Japan), and classified according to a vitreous opacity severity scale. Results: Thirty eyes of 21 patients were included in this study. The average age was 56 years. Symptom duration ranged from 1 to more than 365 days. The most common cause of vitreous floaters was posterior vitreous detachment (63.3%), followed by vitreous syneresis (23.3%), asteroid hyalosis (10%) and vitreous hemorrhage (3.3%). Opacities were classified as Grade 1 in three eyes (10%), Grade 2 in 10 eyes (33.3%), Grade 3 in 11 eyes (36.6%), Grade 4 in two eyes (6.6%) and Grade 5 in four eyes (13.3%). Patients with Grade 1 opacities were younger than patients with opacities Grade 2 or greater. A visible Weiss ring could be identified in 0% of eyes with Grade 1 opacities, 40% of eyes with Grade 2 opacities, 100% of eyes with Grade 3 opacities, and 100% of eyes with Grade 4 opacities. In patients with Grade 5 opacities, a Weiss ring could not be identified. Conclusion: Dynamic ultra-widefield IRcSLO imaging is a useful tool to evaluate patients with vitreous floaters. It allows for accurate visualization of the number, density, and behavior of the shadows that vitreous opacities project over a very wide area of the retina, which has a positive correlation with patient perception of floaters. Full article

The study of Near-Earth Asteroids (NEA) is crucial for human safety. Small hazardous asteroids with small radar cross sections are not easy to detect, track, and characterize due to the small signal-to-noise ratio (SNR) of the radar echo. This manuscript describes the results obtained for the application of a feed-forward neural network (FFNN) denoising methodology to NEA data obtained from the Goldstone Solar System Radar (GSSR). We demonstrate an increase in the signal level of up to ×4 the original value—in terms of sigma above the mean noise—when applying the FFNN denoising technique to radar Z-score normalized Binary Phase Code (BPC) images. This improvement benefits better radar detection of NEAs in general. Reducing the noise background level for antennas that have lower aperture, e.g., 34 m dishes, enables the use of FFNN denoising to improve visual detections on those noisier conditions. In addition, reducing noise level benefits shorter integration times of the data to obtain adequate signal levels. When talking about detection of small bodies crossing the antenna beam, since the asteroids or debris can move across the beam quite fast, it is relevant to reduce the integration time to allow for an increased number of independent pieces of information crossing the target through the antenna beam. The increased distance between the signal level and the noise level enables a better detection of the small-bodies at shorter integration times and therefore would be very useful for the detection of objects in the cis-lunar space. Full article

It is of great significance to apply the object detection methods to automatically detect boulders from planetary images and analyze their distribution. This contributes to the selection of candidate landing sites and the understanding of the geological processes. This paper improves the state-of-the-art object detection method of YOLOv5 with attention mechanism and designs a pyramid based approach to detect boulders from planetary images. A new feature fusion layer has been designed to capture more shallow features of the small boulders. The attention modules implemented by combining the convolutional block attention module (CBAM) and efficient channel attention network (ECA-Net) are also added into YOLOv5 to highlight the information that contribute to boulder detection. Based on the Pascal Visual Object Classes 2007 (VOC2007) dataset which is widely used for object detection evaluations and the boulder dataset that we constructed from the images of Bennu asteroid, the evaluation results have shown that the improvements have increased the performance of YOLOv5 by 3.4% in precision. With the improved YOLOv5 detection method, the pyramid based approach extracts several layers of images with different resolutions from the large planetary images and detects boulders of different scales from different layers. We have also applied the proposed approach to detect the boulders on Bennu asteroid. The distribution of the boulders on Bennu asteroid has been analyzed and presented. Full article

Purpose: To assess preliminarily the efficacy and safety of a relatively new surgical modification of phacovitrectomy in eyes with cataract and visually significant asteroid hyalosis (AH). Materials and methods: Prospective, noncomparative, interventional case series of six eyes of six patients (mean age 75.6 years; 1 woman, 5 men) with cataract and visually significant AH treated with a novel surgical technique—a phacoemulsification with anterior vitrectomy through posterior capsulorhexis and intraocular lens (IOL) implantation. Main outcome measures were: best-corrected visual acuity (BCVA), intraocular pressure (IOP), IOL centration, complications. Mean follow-up was 39.17 ± 4.31 months. Results: The mean BCVA (Snellen) improved from 0.26 ± 0.18 to 0.73 ± 0.33 at the end of the follow-up. IOP was in the normal range, and no problems with IOL fixation were observed at the end of the follow-up. No post-operative complications, retinal detachment, retinal tears, macular edema or prolonged inflammation were observed. Conclusions: The presented new surgical technique seems to be a safe and efficacious method to treat cataract with visually significant asteroid hyalosis. Full article

Planetary Defense (PD) has become a critical effort of protecting our home planet by discovering potentially hazardous objects (PHOs), simulating the potential impact, and mitigating the threats. Due to the lack of structured architecture and framework, pertinent information about detecting and mitigating near earth object (NEO) threats are still dispersed throughout numerous organizations. Scattered and unorganized information can have a significant impact at the time of crisis, resulting in inefficient processes, and decisions made on incomplete data. This PD Mitigation Gateway (pd.cloud.gmu.edu) is developed and embedded within a framework to integrate the dispersed, diverse information residing at different organizations across the world. The gateway offers a home to pertinent PD-related contents and knowledge produced by the NEO mitigation team and the community through (1) a state-of-the-art smart-search discovery engine based on PD knowledge base; (2) a document archiving and understanding mechanism for managing and utilizing the results produced by the PD science community; (3) an evolving PD knowledge base accumulated from existing literature, using natural language processing and machine learning; and (4) a 4D visualization tool that allows the viewers to analyze near-Earth approaches in a three-dimensional environment using dynamic, adjustable PHO parameters to mimic point-of-impact asteroid deflections via space vehicles and particle system simulations. Along with the benefit of accessing dispersed data from a single port, this framework is built to advance discovery, collaboration, innovation, and education across the PD field-of-study, and ultimately decision support. Full article