Trajectory-based launch vehicle performance analysis for design-space exploration in conceptual design

Trajectory optimization is an important part of launch vehicle conceptual design. Current methods for trajectory optimization involve numerical analysis, are computationally expensive and require trajectory experts in the loop, thus limiting efforts for design space exploration. A simplified performance analysis, like the rocket equation, is much better suited to the types of studies desired in conceptual design, where thousands of vehicles can be considered and compared. Unfortunately, the rocket equation does not take into account trajectory losses and therefore does not provide an accurate measure of performance. The lack of a fast and accurate method to evaluate launch vehicle performance represents a gap in the current capability that will be addressed in this thesis. The goal of this research is to formulate and implement a performance analysis method in the form of the rocket equation (i.e. closed-form) that takes into account the trajectory losses considered in a numerical trajectory analysis method. This goal is achieved by generating a surrogate model of launch vehicle trajectory data. Several challenges arise when generating this data in an automated fashion. For this reason, extreme value theory is used in conjunction with an industry standard optimization method. The trajectory problem is statistically posed finding the extreme value of a distribution representing the performance of all possible trajectories. The process of generating a surrogate model is formulated into a method named RAPTOR (Rapid Trajectory Optimization Routine). The method is successfully implemented on the Delta IV Heavy launch vehicle. Implementation of the RAPTOR method results in a capability that enables rapid and accurate performance evaluation of launch vehicles.Ph.D

Surrogate Modeling of Orbital Decay of Lunar Orbits

Presented at AIAA SciTech Forum 2023Operations in cislunar space are expected to greatly increase over the next decade, which will place a heightened demand on satellites operating in cislunar space. The orbit selection of the satellites is a key parameter of the mission. Orbital decay can present significant challenges for some lunar orbits due to gravitational perturbations. This study focuses on developing a fast method to assess the decay of lunar orbits. The method is based on modeling lunar orbits propagation in the presence of these perturbations to quantify orbital decay as a function of orbital parameters, then using the model to generate data and fit surrogate models. Results from this effort will enable decision makers to trade performance and station-keeping costs associated with relevant lunar orbits

Augmenting Parametric Optimal Ascent Trajectory Modeling with Graph Theory

It has been well documented that decisions made in the early stages of Conceptual and Pre-Conceptual design commit up to 80% of total Life-Cycle Cost (LCC) while engineers know the least about the product they are designing [1]. Once within Preliminary and Detailed design however, making changes to the design becomes far more difficult to enact in both cost and schedule. Primarily this has been due to a lack of detailed data usually uncovered later during the Preliminary and Detailed design phases. In our current budget-constrained environment, making decisions within Conceptual and Pre-Conceptual design which minimize LCC while meeting requirements is paramount to a program's success. Within the arena of launch vehicle design, optimizing the ascent trajectory is critical for minimizing the costs present within such concerns as propellant, aerodynamic, aeroheating, and acceleration loads while meeting requirements such as payload delivered to a desired orbit. In order to optimize the vehicle design its constraints and requirements must be known, however as the design cycle proceeds it is all but inevitable that the conditions will change. Upon that change, the previously optimized trajectory may no longer be optimal, or meet design requirements. The current paradigm for adjusting to these updates is generating point solutions for every change in the design's requirements [2]. This can be a tedious, time-consuming task as changes in virtually any piece of a launch vehicle's design can have a disproportionately large effect on the ascent trajectory, as the solution space of the trajectory optimization problem is both non-linear and multimodal [3]. In addition, an industry standard tool, Program to Optimize Simulated Trajectories (POST), requires an expert analyst to produce simulated trajectories that are feasible and optimal [4]. In a previous publication the authors presented a method for combatting these challenges [5]. In order to bring more detailed information into Conceptual and Pre-Conceptual design, knowledge of the effects originating from changes to the vehicle must be calculated. In order to do this, a model capable of quantitatively describing any vehicle within the entire design space under consideration must be constructed. This model must be based upon analysis of acceptable fidelity, which in this work comes from POST. Design space interrogation can be achieved with surrogate modeling, a parametric, polynomial equation representing a tool. A surrogate model must be informed by data from the tool with enough points to represent the solution space for the chosen number of variables with an acceptable level of error. Therefore, Design Of Experiments (DOE) is used to select points within the design space to maximize information gained on the design space while minimizing number of data points required. To represent a design space with a non-trivial number of variable parameters the number of points required still represent an amount of work which would take an inordinate amount of time via the current paradigm of manual analysis, and so an automated method was developed. The best practices of expert trajectory analysts working within NASA Marshall's Advanced Concepts Office (ACO) were implemented within a tool called multiPOST. These practices include how to use the output data from a previous run of POST to inform the next, determining whether a trajectory solution is feasible from a real-world perspective, and how to handle program execution errors. The tool was then augmented with multiprocessing capability to enable analysis on multiple trajectories simultaneously, allowing throughput to scale with available computational resources. In this update to the previous work the authors discuss issues with the method and solutions

Haematopoietic and cardiac GPR55 synchronize post-myocardial infarction remodelling

While classical cannabinoid receptors are known to crucially impact on myocardial infarction (MI) repair, a function of the cannabinoid-sensitive receptor GPR55 herein is poorly understood. We investigated the role of GPR55 in cardiac physiology and post-MI inflammation and remodelling. Global GPR55-/- and wildtype (WT) mice were basally characterized or assigned to 1, 3 or 28~days permanent MI and subsequently analysed via pro-inflammatory and pro-hypertrophic parameters. GPR55-/- deficiency was basally associated with bradycardia, increased diastolic LV volume and sarcomere length and a subtle inflammatory phenotype. While infarct size and myeloid cell infiltration were unaffected by GPR55 depletion, acute cardiac chemokine production was prolonged post-MI. Concurrently, GPR55-/- hearts exhibited a premature expansion of pro-reparative and phagocytic macrophages paralleled by early up-regulation of extracellular matrix (ECM) factors 3~days post-MI, which could be mimicked by sole haematopoietic GPR55 depletion. Moreover, global GPR55 deficiency mitigated MI-induced foetal gene re-programming and cardiomyocyte hypertrophy, culminating in aggravated LV dilatation and infarct expansion. GPR55 regulates cardiac homeostasis and ischaemia responses by maintaining adequate LV filling and modulating three crucial processes post-MI: wound healing kinetics, cardiomyocyte hypertrophy and maladaptive remodelling

Growth of Ga₂O₃ by furnace oxidation of GaN studied by perturbed angular correlations

Ga₂O₃ is a promising material for use in “solar-blind” UV-detectors which can be produced efficiently by oxidation of GaN. In this study we focus on the evolution of the oxide layer when GaN is heated in air. The experimental method applied is the perturbed angular correlation (PAC) spectroscopy of γ-rays emitted by radioactive nuclides, here ¹¹¹Cd and ¹⁸¹Ta, whose parent nuclei are ion implanted into films of GaN grown on sapphire. As the emission pattern for nuclei in GaN is clearly distinct from that of nuclei in Ga₂O₃, the fraction of probe nuclei in the oxide layer can be directly measured and allows to follow the time dependent growth of the oxide on a scale of less than 100 nm. Additional measurements were carried out with the oxidized sample held at fixed temperatures in the temperature range from 19 K to 973 K showing transitions between the hyperfine interactions of ¹¹¹Cd in the oxide matrix both at high and low temperatures. A model for these transitions is proposed.Instituto de Física La Plat

What Do Men with Lower Urinary Tract Symptoms Expect from a Urologist in Secondary Care?

Purpose: To identify the expectations of men with LUTS referred to a urologist and to study the association between those expectations and satisfaction with the care provided. Methods: In this prospective cohort study, adult men with LUTS completed a questionnaire before their first outpatient appointment, and again at 6 and 12 weeks. The questionnaires included IPSS and OABq-SF, and self-constructed questions on patient expectations, outcome of expectations and satisfaction. Results: Data from 182 participants showed positive expectations about the urologist performing examinations, providing explanations and finding the underlying cause, but mostly neutral expectations for treatment plans and outcomes. Positive treatment expectations were associated with positive expectations about outcomes after physiotherapy, drug treatment and surgery. Higher symptom scores and age were associated with higher expectations about drug treatment. Expectations were subjectively and objectively fulfilled for 66.4% and 27.3%, respectively. Symptom improvement (decrease in IPSS scores) was significantly more in men with objectively fulfilled expectations than in men with no unfulfilled expectations. No significant difference was present between men with subjectively fulfilled expectations and men with unfulfilled expectations. However, satisfaction was significantly higher for patients with subjectively fulfilled expectations at 6 and 12 weeks compared with those who had unfulfilled expectations. Conclusion: Most men referred to a urologist with LUTS do express clear expectations about treatment in secondary care. Patients with higher expectations for treatment outcomes are more likely to expect to receive that treatment. Satisfaction with the care of a urologist is also higher when patients self-report that they receive the treatment they expected