3D Reconstruction of Small Solar System Bodies using Rendered and Compressed Images

Synthetic image generation and reconstruction of Small Solar System Bodies and the influence of compression is becoming an important study topic because of the advent of small spacecraft in deep space missions. Most of these missions are fly-by scenarios, for example in the Comet Interceptor mission. Due to limited data budgets of small satellite missions, maximising scientific return requires investigating effects of lossy compression. A preliminary simulation pipeline had been developed that uses physics-based rendering in combination with procedural terrain generation to overcome limitations of currently used methods for image rendering like the Hapke model. The rendered Small Solar System Body images are combined with a star background and photometrically calibrated to represent realistic imagery. Subsequently, a Structure-from-Motion pipeline reconstructs three-dimensional models from the rendered images. In this work, the preliminary simulation pipeline was developed further into the Space Imaging Simulator for Proximity Operations software package and a compression package was added. The compression package was used to investigate effects of lossy compression on reconstructed models and the possible amount of data reduction of lossy compression to lossless compression. Several scenarios with varying fly-by distances ranging from 50 km to 400 km and body sizes of 1 km and 10 km were simulated and compressed with lossless and several quality levels of lossy compression using PNG and JPEG 2000 respectively. It was found that low compression ratios introduce artefacts resembling random noise while high compression ratios remove surface features. The random noise artefacts introduced by low compression ratios frequently increased the number of vertices and faces of the reconstructed three-dimensional model

Limitations of Initial Orbit Determination Methods for Low Earth Orbit CubeSats with Short Arc Orbital Passes

This thesis will focus on the performance of angles only initial orbit determi- nation (IOD) methods on observational data of low Earth orbit (LEO) CubeSats. Using data obtained by Lockheed Martin’s Space Object Tracking (SpOT) facil- ity, four methods: Gauss, Double-R, Gooding and Assumed Circular, will use different amounts of orbital arc to determine which methods perform the best in the short arc regime of less than 10 degrees of orbital arc. Once the best method for estimating the orbit is determined, there will be analysis on whether these IOD methods are accurate enough to predict a secondary observation session. Finally non-linear regression will be performed to determine if the error metrics follow a predictable trend based on how much orbital arc is seen by the observer. It was determined that above a certain amount of orbital arc, angles only IOD methods can reliably predict a secondary observation session to facilitate more observations. Below 4 degrees of orbital arc, which is around 60 seconds of ob- serving time for LEO objects, none of the methods were able to reliably predict a secondary observation session. The Assumed Circular method was the best method for observing LEO CubeSats because it forces the IOD solution to be circular, which limits the error in the shape of the orbit as the amount of orbital arc decreases. Finally, many metrics follow an exponential trend when compared to the orbital arc. Thus, the amount of orbital arc seen is a strong predictor for the accuracy of the angles only IOD solutions

Optimal Designs of Mobile Nuclear Engines to Power Manned Vehicles On Mars

This work develops original conceptual designs for compact nuclear fission reactor engines to power robust mobile equipment operating on the surface of the planet Mars. This is a nuclear application area not well explored in previous publications. Some novel analytical approaches are developed herein, including the application of optimal control theory to minimize radiation shielding mass. This work also provides the first study of using another planet\u27s atmosphere to implement open-cycle thermal conversion systems. To power equipment on Mars for extended durations at sustained power levels ranging from one hundred horsepower to several thousand horsepower, there is no practical alternative to a nuclear fission heat source. Design difficulties arise from mobility\u27s need to restrict engine size and mass, each of which is, in turn, determined by the schemes chosen for thermal conversion waste heat rejection and for neutron and gamma radiation shielding. The conceptual design solutions pursued herein entirely avoid a large waste heat rejection radiator or low pressure heat exchanger by instead using the martian air directly as the thermal conversion fluid. This Open Brayton Cycle implementation unconventionally employs large-diameter radial-flow compressor/turbine designs for the lower pressure air-flow stages in order to obtain sufficient efficiency from the low pressure martian air. Design prescriptions and analyses for these rotating components are included. The radiation shielding mass has been minimized by numerical algorithms developed as part of this work to solve the Euler-Lagrange equations for a minimum mass shield meeting stated radiation leakage requirements. In addition, a risk-balancing approach is taken to setting those radiation requirements in order to avoid excessive conservatism

Flower constellation optimization and implementation

Satellite constellations provide the infrastructure to implement some of the most important global services of our times both in civilian and military applications, ranging from telecommunications to global positioning, and to observation systems. Flower Constellations constitute a set of satellite constellations characterized by periodic dynamics. They have been introduced while trying to augment the existing design methodologies for satellite constellations. The dynamics of a Flower Constellation identify a set of implicit rotating reference frames on which the satellites follow the same closed-loop relative trajectory. In particular, when one of these rotating reference frames is “Planet Centered, Planet Fixed”, then all the orbits become compatible (or resonant) with the planet; consequently, the projection of the relative path on the planet results in a repeating ground track. The satellite constellations design methodology currently most utilized is the Walker Delta Pattern or, more generally, Walker Constellations. The set of orbital planes and initial spacecraft positions are represented by a set of only three integers and two real parameters rather than by all the orbital elements; Flower Constellations provide a more general framework in which most of the former restrictions are removed, by allowing the use of resonant elliptical orbits. Flower Constellations can represent hundreds of spacecraft with a set of 6 integers and 5 real parameters only and existing constellations can be easily reproduced. How to design a Flower Constellation to satisfy specific mission requirements is an important problem for promoting the acceptance of this novel concept by the space community. Therefore one of the main goals of this work is that of proposing design techniques that can be applied to satisfy practical mission requirements. The results obtained by applying Global optimization techniques, such as Genetic Algorithms, to some relevant navigation and Earth observation space-based systems show that the Flower Constellations not only are as effective asWalker Constellations, but can also be applied to non-traditional constellation problem domains, such as regional coverage and reconnaissance

LIPIcs, Volume 274, ESA 2023, Complete Volume

LIPIcs, Volume 274, ESA 2023, Complete Volum

Remote Sensing of the Oceans

This book covers different topics in the framework of remote sensing of the oceans. Latest research advancements and brand-new studies are presented that address the exploitation of remote sensing instruments and simulation tools to improve the understanding of ocean processes and enable cutting-edge applications with the aim of preserving the ocean environment and supporting the blue economy. Hence, this book provides a reference framework for state-of-the-art remote sensing methods that deal with the generation of added-value products and the geophysical information retrieval in related fields, including: Oil spill detection and discrimination; Analysis of tropical cyclones and sea echoes; Shoreline and aquaculture area extraction; Monitoring coastal marine litter and moving vessels; Processing of SAR, HF radar and UAV measurements

Evaluation of fatigue response of a carbonate clay till beneath wind turbine foundation

This thesis describes full-scale field monitoring and analysis of an onshore shallow wind turbine foundation and an associated laboratory testing program. The aim of the study was to investigate the soil-structure interaction under coupled cyclic vertical-horizontal-moment loading. This involved simulating the soil element behavior in controlled laboratory tests, evaluating the accumulated cyclic soil damage and correlating this with the observed wind and turbine responses. The results form an important part of the ‘wind-chain’, providing information for optimizing the performance of wind turbines, extending their operational lifespans and potentially for development of structural health monitoring systems. The field monitoring systems for the foundation, tower and wind fields are described, and the responses for high/low probability wind events are discussed. The identified spectral peaks from the field measurements corresponded with the literature. The measured foundation response was compared to numerical elastic models and a finite element model of the turbine foundation of study with some success. The laboratory testing program is described and the implications for assessing the soil strength and stiffness degradation due to the associated small loading cycles during the operation of the wind turbine are quantified and examined. A threshold strain value of cyclic degradation is identified and the degradation parameter for a compilation of strain levels for different stress states is developed. An example degradation calculation from the field measurements for a time history is carried out with some success