Reconfigurable satellite constellations for geo-spatially adaptive Earth observation missions

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 145-151).Continuously increasing demand for Earth observation in atmospheric research, disaster monitoring, and intelligence, surveillance and reconnaissance (ISR) has been met by responsive architectures such as unmanned aerial systems (UAS) or artificial satellites. Space-based architectures can provide non-dominated design solutions on the utility-cost curve compared to alternate architectures through the use of two approaches: (1) reducing satellite manufacturing and launch costs and (2) introducing reconfigurability to the satellite constellations. Reconfigurable constellations (ReCons) enable fast responses to access targets of interest while providing global monitoring capability from space. The wide-area coverage and fast responses provided ReCon can complement high-resolution imagery provided by UAS. A newly proposed ReCon framework improves the model fidelity of previous approaches by utilizing Satellite Tool Kit (STK) simulations and Earth observation mission databases. This thesis investigates the design and optimization of ReCon in low Earth orbits. A multidisciplinary simulation model is developed, to which optimization techniques are applied for both single-objective and multi-objective problems. In addition to the optimized baseline ReCon design, its variants are also considered as case studies. Future work will potentially co-optimize ReCon and UAS-like systems.by Sung Wook Paek.S.M

Optimization of Reconfigurable Satellite Constellations Using Simulated Annealing and Genetic Algorithm

Agile Earth observation can be achieved with responsiveness in satellite launches, sensor pointing, or orbit reconfiguration. This study presents a framework for designing reconfigurable satellite constellations capable of both regular Earth observation and disaster monitoring. These observation modes are termed global observation mode and regional observation mode, constituting a reconfigurable satellite constellation (ReCon). Systems engineering approaches are employed to formulate this multidisciplinary problem of co-optimizing satellite design and orbits. Two heuristic methods, simulated annealing (SA) and genetic algorithm (GA), are widely used for discrete combinatorial problems and therefore used in this study to benchmark against a gradient-based method. Point-based SA performed similar or slightly better than the gradient-based method, whereas population-based GA outperformed the other two. The resultant ReCon satellite design is physically feasible and offers performance-to-cost(mass) superior to static constellations. Ongoing research on observation scheduling and constellation management will extend the ReCon applications to radar imaging and radio occultation beyond visible wavelengths and nearby spectrums. Keywords: Earth observation; remote sensing; satellite constellation; reconfigurability; repeat ground tracks; simulated annealing; genetic algorith

Space-based Earth remote sensing: Part 1. Satellite orbit theory

The development of oceanography and meteorology has greatly benefited from remotely sensed satellite data of the atmosphere and ocean. For oceanographers, meteorologists, hydrologists and climatologists to obtain high-quality satellite data, orbits along which the satellites move must be designed carefully. For this reason, Sun-synchronous, repeat ground track orbits have traditionally been used for visible-wavelength and infrared Earth observations. As the needs for varied datasets are growing, however, new classes of Earth-observing missions are emerging such as interferometry and radiometry to name a few. On the other side, satellite platforms and onboard sensors are getting more compact and less expensive, allowing developing nations to launch their own satellites and under-researched parts of the Earth be studied. In light of these changes, this paper introduces new types of satellite orbits from celestial mechanics perspectives, whose applications will be detailed further in the follow-up work

Primary Culture of Central Neurocytoma: A Case Report

A seventeen-year-old female patient was admitted with sudden-onset of headache and vomiting. Brain magnetic resonance imaging demonstrated a heterogeneously enhancing tumour in the left lateral ventricle. The tumour was removed and confirmed as a central neurocytoma (CN). For the residual tumour in the left lateral ventricle, gamma knife stereotactic radiosurgery was done at fifteen months after the initial surgery. Tumour recurred in the 4th ventricle at 5 yr after initial surgery. The tumour was removed and proved as a CN. In vitro primary culture was done with both tumours obtained from the left lateral ventricle and the 4th ventricle, respectively. Nestin, a neuronal stem cell marker was expressed in reverse Transcriptase-Polymerase Chain Reaction of both tumors. Both tumours showed different morphology and phenotypes of neuron and glia depending on the culture condition. When cultured in insulin, transferrin selenium and fibronectin media with basic fibroblast growth factors, tumour cells showed neuronal morphology and phenotypes. When cultured in the Dulbeco's Modified Essential Media with 20% fetal bovine serum, tumors cells showed glial morphology and phenotypes. It is suggested that CN has the characteristics of neuronal stem cells and potential to differentiate into mature neuron and glial cells depending on the environmental cue

Asteroid deflection campaign design integrating epistemic uncertainty

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2016.Cataloged from PDF version of thesis.Includes bibliographical references (pages 241-249).Planetary defense, or asteroid collision avoidance, has been gaining interest with recent meteor or fly-by events, including the Chelyabinsk meteor that entered the Earth's atmosphere and exploded over Russia in 2013. Past or planned robotic missions to near-Earth asteroids are expected to provide an excellent opportunity to demonstrate asteroid deflection techniques. However, applying a deflection technique to a hazardous asteroid in real-world situations requires extreme care for decision makers due to inherent uncertainty. The forms of uncertainty can be epistemic or aleatoric. Epistemic uncertainty can be reduced by replenishing incomplete information with better observations, whereas stochastic uncertainty cannot be reduced owing to its randomness. Although we cannot reduce stochastic uncertainty itself, we can come up with a plan which is robust to random uncertainty, by reducing epistemic uncertainty. This thesis develops a methodology to design an asteroid deflection campaign that consists of multiple mission stages. The first stage serves as a precursor whose type can achieve different amounts of uncertainty reduction. With this in-situ information obtained by precursors, the follow-up stage may adapt its impactor design. The methodology is implemented in the Asteroid Deflection Integrating Epistemic Uncertainty (ADIEU) framework. The ADIEU framework is demonstrated in deflection campaigns of select near- Earth asteroids. Generation of campaign solutions over a 15-year period, with different confidence requirements, requires up to 125,000 full-factorial runs and 400 optimization runs per asteroid. Results show that campaigns which consider and reduce epistemic uncertainty can both decrease launch mass and increase robustness. However, there are also cases, under extreme conditions, where a single-stage mission turns out to perform best. The performance envelopes of these different approaches are superposed to generate a decision map for use as a visual aid. Finally, this thesis concludes by outlining future work to refine the framework, as well as potential uses of the methodology in terrestrial applications.by Sung Wook Paek.Ph. D

Design and Synthesis of Small Molecules as Potent Staphylococcus aureus Sortase A Inhibitors

The widespread and uncontrollable emergence of antibiotic-resistant bacteria, especially methicillin-resistant Staphylococcus aureus, has promoted a wave of efforts to discover a new generation of antibiotics that prevent or treat bacterial infections neither as bactericides nor bacteriostats. Due to its crucial role in virulence and its nonessentiality in bacterial survival, sortase A has been considered as a great target for new antibiotics. Sortase A inhibitors have emerged as promising alternative antivirulence agents against bacteria. Herein, the structural and preparative aspects of some small synthetic organic compounds that block the pathogenic action of sortase A have been described

Asteroid Deflection Campaign Design Integrating Epistemic Uncertainties

Asteroid deflection entails multiple sources of epistemic uncertainties and stochastic uncertainties. Epistemic uncertainties can be reduced by replenishing incomplete information with a better means of observation, whereas stochastic uncertainties are inherent and irreducible owing to their randomness. Our understanding of asteroid deflection is largely limited by lack of in-situ data or full-scale experiments. Reducing these epistemic uncertainties in (1) the physical properties of asteroids or (2) the consequences of human interference will drastically benefit our mitigation efforts against their hazards. Much of previous literature concentrated on single-stage missions or simple asteroid models with fixed physical attributes, making it inadequate to handle epistemic or stochastic uncertainties. To fill this gap, this paper tries to incorporate different kinds of uncertainties within a campaign design framework. In a multi-stage campaign, a precursor is deployed first to reduce epistemic uncertainties. Because stochastic uncertainties cannot be reduced by nature, the campaign should be optimized to maximize its robustness against the worst random situations. Finally, whether or not a two-stage campaign is better than a single-stage mission can be visualized as a decision map for decision-makers. The paper analyzes a hypothetical scenario of deflecting 99942 Apophis and discusses future work

Small-satellite synthetic aperture radar for continuous global biospheric monitoring: a review

Space-based radar sensors have transformed Earth observation since their first use by Seasat in 1978. Radar instruments are less affected by daylight or weather conditions than optical counterparts, suitable for continually monitoring the global biosphere. The current trends in synthetic aperture radar (SAR) platform design are distinct from traditional approaches in that miniaturized satellites carrying SAR are launched in multiples to form a SAR constellation. A systems engineering perspective is presented in this paper to track the transitioning of space-based SAR platforms from large satellites to small satellites. Technological advances therein are analyzed in terms of subsystem components, standalone satellites, and satellite constellations. The availability of commercial satellite constellations, ground stations, and launch services together enable real-time SAR observations with unprecedented details, which will help reveal the global biomass and their changes owing to anthropogenic drivers. The possible roles of small satellites in global biospheric monitoring and the subsequent research areas are also discussed

SATELLITE CONSTELLATION DESIGN FOR THE SOLVE MISSION INVESTIGATING DIURNAL CYCLES OF VEGETATION PHENOMENA

This paper discusses the problem of finding an optimal satellite constellation for the SOLVE (Satellites Observing Lakes and Vegetation Environments) Mission. A key requirement of this mission is a temporal resolution of several observations per day. A semi-analytical approach is proposed. After some analytical design steps which reduces the problem space to circular sun synchronous orbits, a genetic algorithm is used for finding all remaining orbital parameters. The result is an easy to use tool which allows to study cost impact from given science requirements enabling a good understanding of the relation between temporal, spatial resolution and cost

Satellite constellation design algorithm for remote sensing of diurnal cycles phenomena

This paper proposes an algorithm to find the smallest satellite constellation satisfying a given set of Earth observation requirements. This methodology is exemplified with the Satellites Observing Lakes and Vegetation Environments (SOLVE) study, which aims at deploying a fleet of small satellites carrying miniaturized hyperspectral spectrometers. A key requirement of this mission is a high temporal resolution through which the ground target can be observed several times a day. Hourly observations are required in this mission in order to capture diurnal changes in water quality and vegetation environments. Given sensor specifications and observation requirements, the proposed algorithm determines orbital parameters of an optimal constellation design via a semi-analytical approach. This approach reveals trade-offs amongst performance metrics and deployment cost, providing better physical intuition for decision making compared to stochastic optimization. (C) 2018 COSPAR. Published by Elsevier Ltd. All rights reserved