Person:
Steffens, Michael J.

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Publication Search Results

Now showing 1 - 6 of 6
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    Optimal Deployment Strategies for Cislunar PNT+C Architectures
    (Georgia Institute of Technology, 2024-01) Gabhart, Austin ; Drosendahl, Madilyn ; Robertson, Bradford E. ; Steffens, Michael J. ; Mavris, Dimitri N.
    Cislunar operations are expected to rise dramatically within the next decade, requiring a comparable increase in PNT and communications services. However, current PNT systems are at capacity and need to be augmented to serve a cislunar space domain, specifically in the form of novel cislunar PNT architectures. This paper studies the problem of the deployment of PNT and communications satellites, specifically, the problem of deployment strategies spanning multiple stages over extended periods of time. A set of stage definitions will be determined along with areas of potential user activity. A novel application of the hidden gene genetic algorithm to the constellation optimization problem is presented. A design space exploration is presented with comparisons of circular and elliptical constellations. Optimization results from the first stage are also provided. It is shown that acceptable performance can be achieved with a low number of deployed satellites and that strong trade-offs exist between performance and stability.
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    Surrogate Modeling of Orbital Decay of Lunar Orbits
    (AIAA, 2023-01) Varoqui, Maxime ; Steffens, Michael J. ; Mavris, Dimitri N.
    Operations 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.
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    Tradespace Exploration and Analysis Using Mission Effectiveness in Aircraft Conceptual Design
    (Georgia Institute of Technology, 2020-01) Braafladt, Alexander ; Steffens, Michael J. ; Mavris, Dimitri N.
    The success of aircraft development programs is based in requirements. Requirements are the starting point for the program and translate the key points of the operational need into what is eventually built. In many recent Air Force programs, significant cost and schedule challenges have been met. These challenges have compounded with operational requirements for improvement based on advancing and proliferating threats. The compounding issues drive a need to improve the development process. The need can be met in part by recent advancements in modeling approaches and computational frameworks. These advancements improve how operational effectiveness can be analyzed throughout design to inform the process. The work in this paper focuses on including operations analysis in the conceptual sizing and synthesis process. A modeling framework for design that can be used as a component of a decision support and requirements analysis environment is presented. The modeling framework is used in a test case of the basic conceptual design of a new tactical fighter. Results from the test case include an exploration of how changes to requirements impact the expected operational effectiveness. The critical requirements from the test case were identified and an example of a trade between critical variables was considered.
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    Exploring the Design Space of an Electric Ship using a Probabilistic Technology Evaluation Methodology
    (Georgia Institute of Technology, 2019-08) McNabb, Jeffrey ; Robertson, Nicole A. ; Steffens, Michael J. ; Sudol, Alicia ; Mavris, Dimitri N. ; Chalfant, Julie
    With the advent of new technologies for electric ships, there is a need for a robust methodology to quantitatively evaluate their impact on the performance of a ship, while accounting for the uncertain nature of their parameters. To that end, this paper gives an overview of the Technology Identification, Evaluation, and Selection, or TIES, methodology as applied a 10kton surface combatant. This case study highlights the ability of TIES to aid in a broad exploration of the design space, by giving designers key tools that allow them to show in a traceable manner the tradeoffs involved in infusing technologies and making other design choices, as well as which designs best meet different sets of Figures of Merit. This ultimately allows decision-makers to determine what technologies or design choices to invest in to yield a ship with the performance parameters that will best serve the needs of its stakeholders.
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    Trajectory-based launch vehicle performance analysis for design-space exploration in conceptual design
    (Georgia Institute of Technology, 2016-07-20) Steffens, Michael J.
    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.
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    A combined global and local methodology for launch vehicle trajectory design-space exploration and optimization
    (Georgia Institute of Technology, 2014-04-09) Steffens, Michael J.
    Trajectory optimization is an important part of launch vehicle design and operation. With the high costs of launching payload into orbit, every pound that can be saved increases affordability. One way to save weight in launch vehicle design and operation is by optimizing the ascent trajectory. Launch vehicle trajectory optimization is a field that has been studied since the 1950’s. Originally, analytic solutions were sought because computers were slow and inefficient. With the advent of computers, however, different algorithms were developed for the purpose of trajectory optimization. Computer resources were still limited, and as such the algorithms were limited to local optimization methods, which can get stuck in specific regions of the design space. Local methods for trajectory optimization have been well studied and developed. Computer technology continues to advance, and in recent years global optimization has become available for application to a wide variety of problems, including trajectory optimization. The aim of this thesis is to create a methodology that applies global optimization to the trajectory optimization problem. Using information from a global search, the optimization design space can be reduced and a much smaller design space can be analyzed using already existing local methods. This allows for areas of interest in the design space to be identified and further studied and helps overcome the fact that many local methods can get stuck in local optima. The design space included in trajectory optimization is also considered in this thesis. The typical optimization variables are initial conditions and flight control variables. For direct optimization methods, the trajectory phase structure is currently chosen a priori. Including trajectory phase structure variables in the optimization process can yield better solutions. The methodology and phase structure optimization is demonstrated using an earth-to-orbit trajectory of a Delta IV Medium launch vehicle. Different methods of performing the global search and reducing the design space are compared. Local optimization is performed using the industry standard trajectory optimization tool POST. Finally, methods for varying the trajectory phase structure are presented and the results are compared.