Organizational Unit:

Space Systems Design Laboratory (SSDL)

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https://hdl.handle.net/1853/70747

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Organizational Unit

Daniel Guggenheim School of Aerospace Engineering

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https://finding-aids.library.gatech.edu/agents/corporate_entities/1138

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Publication Search Results

Now showing 1 - 10 of 107

Computational Fluid Dynamics Validation of a Single, Central Nozzle Supersonic Retropropulsion Configuration

(Georgia Institute of Technology, 2009-05) Cordell, Christopher E., Jr.

Supersonic retropropulsion provides an option that can potentially enhance drag characteristics of high mass entry, descent, and landing systems. Preliminary flow field and vehicle aerodynamic characteristics have been found in wind tunnel experiments; however, these only cover specific vehicle configurations and freestream conditions. In order to generate useful aerodynamic data that can be used in a trajectory simulation, a quicker method of determining vehicle aerodynamics is required to model supersonic retropropulsion effects. Using computational fluid dynamics, flow solutions can be determined which yield the desired aerodynamic information. The flow field generated in a supersonic retropropulsion scenario is complex, which increases the difficulty of generating an accurate computational solution. By validating the computational solutions against available wind tunnel data, the confidence in accurately capturing the flow field is increased, and methods to reduce the time required to generate a solution can be determined. Fun3D, a computational fluid dynamics code developed at NASA Langley Research Center, is capable of modeling the flow field structure and vehicle aerodynamics seen in previous wind tunnel experiments. Axial locations of the jet terminal shock, stagnation point, and bow shock show the same trends which were found in the wind tunnel, and the surface pressure distribution and drag coefficient are also consistent with available data. The flow solution is dependent on the computational grid used, where a grid which is too coarse does not resolve all of the flow features correctly. Refining the grid will increase the fidelity of the solution; however, the calculations will take longer if there are more cells in the computational grid.
Survivability and Resiliency of Spacecraft and Space-Based Networks: a Framework for Characterization and Analysis, Version 2

(Georgia Institute of Technology, 2008-09-09) Castet, Jean-Francois ; Saleh, Joseph H.

Considerations of survivability and resiliency have always been of importance in the design and analysis of military systems. Over the past two decades, the importance of survivability and resiliency has expanded beyond military systems to include public networks and infrastructure systems. The analysis and assessment of networked systems with respect to survivability has become particularly acute in recent years, as attested to by a growing technical literature on the subject. In this paper, we bring these considerations of survivability and resiliency to bear on spacecraft and space-based networks. We develop a framework for comparing the survivability and resiliency of different space architectures, namely that of a monolithic design and a distributed (or networked) space system architecture. There are multiple metrics along which different space architectures can be benchmarked and compared. We argue that if survivability and resiliency are not accounted for, then the evaluation process is likely to be biased in favor of monolithic spacecraft. We show that if in a given context survivability and resiliency are an important requirement for a particular customer, then a distributed architecture is more likely to satisfy this requirement than a monolithic spacecraft design. We discuss in the context of our framework different classes of threats, as well as the high-frequency and low-frequency system response to (or coping strategies with) these shocks or damaging events. We illustrate the importance of this characterization for a formal definition of survivability and resiliency and a proper quantitative analysis of the subject. Finally, we propose in future work to integrate our framework with a design tool that allows the exploration of the design trade-space of distributed space architecture and show how survivability can be “optimized” or traded against other system attributes.
Survivability and Resiliency of Spacecraft and Space-Based Networks: a Framework for Characterization and Analysis, Version 1

(Georgia Institute of Technology, 2008-09) Castet, Jean-Francois ; Saleh, Joseph H.

Considerations of survivability and resiliency have always been of importance in the design and analysis of military systems. Over the past two decades, the importance of survivability and resiliency has expanded beyond military systems to include public networks and infrastructure systems. The analysis and assessment of networked systems with respect to survivability has become particularly acute in recent years, as attested to by a growing technical literature on the subject. In this paper, we bring these considerations of survivability and resiliency to bear on spacecraft and space-based networks. We develop a framework for comparing the survivability and resiliency of different space architectures, namely that of a monolithic design and a distributed (or networked) space system architecture. There are multiple metrics along which different space architectures can be benchmarked and compared. We argue that if survivability and resiliency are not accounted for, then the evaluation process is likely to be biased in favor of monolithic spacecraft. We show that if in a given context survivability and resiliency are an important requirement for a particular customer, then a distributed architecture is more likely to satisfy this requirement than a monolithic spacecraft design. We discuss in the context of our framework different classes of threats, as well as the high-frequency and low-frequency system response to (or coping strategies with) these shocks or damaging events. We illustrate the importance of this characterization for a formal definition of survivability and resiliency and a proper quantitative analysis of the subject. Finally, we propose in future work to integrate our framework with a design tool that allows the exploration of the design trade-space of distributed space architecture and show how survivability can be “optimized” or traded against other system attributes.
A Value Proposition for Lunar Architectures Utilizing Propellant Re-supply Capabilities

(Georgia Institute of Technology, 2007-09) Young, James ; Wilhite, Alan

The NASA Exploration Systems Architecture Study (ESAS)ⁱⁱ produced a transportation architecture for returning humans to the moon affordably and safely while using commercial services for tasks such as cargo delivery to low earth orbit (LEO). Another potential utilization of commercial services is the delivery of cryogenic propellants to LEO for use in lunar exploration activities. With in-space propellant re-supply available, there is the potential to increase the payload that can be delivered to the lunar surface, increase lunar mission durations, and enable a wider range of lunar missions. The addition of on-orbit propellant resupply would have far-reaching effects on the entire exploration architecture. Currently 70% of the weight delivered to LEO by the cargo launch vehicle is propellant needed for the TLI burn. This is a considerable burden and significantly limits the design freedom of the architecture. The ability of commercial providers to deliver cryogenic propellants to LEO may provide for a less expensive and better performing lunar architecture.
Responsive Space: Concept Analysis, Critical Review, and Theoretical Framework

(Georgia Institute of Technology, 2007-09) Saleh, Joseph H. ; Dubos, Gregory

Customers’ needs are dynamic and evolve in response to unfolding environmental uncertainties. The ability of a company or an industry to address these changing customers’ needs in a timely and cost-effective way is a measure of its responsiveness. In the space industry, a systemic discrepancy exists between the time constants associated with the change of customers’ needs, and the response time of the industry in delivering on-orbit solutions to these needs. Increasingly, the penalties associated with such delays are becoming unacceptable, and space responsiveness is recognized as a strategic imperative in commercial competitive and military environments. In this paper, we provide a critical assessment of the literature on responsive space and introduce a new multi-disciplinary framework for thinking about and addressing issues of space responsiveness. Our framework advocates three levels of responsiveness: a global industry-wide responsiveness, a local stakeholder responsiveness, and an interactive or inter-stakeholder responsiveness. We introduce and motivate the use of “responsiveness maps” for multiple stakeholders. We then identify “levers of responsiveness,” technical spacecraft- and launch-centric, as well as “soft” levers (e.g., acquisition policies) for improving the responsiveness of the space industry. Finally, we propose a series of research questions to aggressively tackle problems associated with space responsiveness.
The Gryphon: A Flexible Lunar Lander Design to Support a Semi-Permanent Lunar Outpost

(Georgia Institute of Technology, 2007-09) Arney, Dale ; Hickman, Joseph ; Tanner, Philip ; Wagner, John ; Wilson, Marc ; Wilhite, Alan W.

A lunar lander is designed to provide safe, reliable, and continuous access to the lunar surface by the year 2020. The NASA Exploration System Architecture is used to initially define the concept of operations, architecture elements, and overall system requirements. The design evaluates revolutionary concepts and technologies to improve the performance and safety of the lunar lander while minimizing the associated cost using advanced systems engineering capabilities and multi-attribute decision making techniques. The final design is a flexible (crew and/or cargo) lander with a side-mounted minimum ascent stage and a separate stage to perform lunar orbit insertion.
Technology Readiness Level, Schedule Risk and Slippage in Spacecraft Design: Data Analysis and Modeling

(Georgia Institute of Technology, 2007-09) Dubos, Gregory F. ; Saleh, Joseph H. ; Braun, Robert D.

Schedule slippage plagues the space industry, and is antinomic with the recent emphasis on space responsiveness. The Government Accountability Office has repeatedly noted the difficulties encountered by the Department of Defense in keeping its acquisition of space systems on schedule, and identified the low Technology Readiness Level (TRL) of the system/payload under development as a principal culprit driving schedule risk and slippage. In this paper, we analyze based on data from past space programs the relationship between technology uncertainty and schedule risk in the acquisition of space systems, and propose an analytical framework to identify appropriate schedule margins for mitigating the risk of schedule slippage. We also introduce the TRL-schedule-risk curves to help program managers make riskinformed decisions regarding the appropriate schedule margins for a given program, or the appropriate TRL to consider should the program’s schedule be exogenously and rigidly constrained. We recommend based on our findings, that the industry adopts and develops schedule risk curves (instead of single schedule point estimates), 2) that these schedule risk curves be made available to policy- and decision-makers in acquisition programs; and 3) that adequate schedule margins be defined according to an agreed upon and acceptable schedule risk level.
Design Space Pruning Techniques for Low-Thrust, Multiple Asteroid Rendezvous Trajectory Design

(Georgia Institute of Technology, 2007-09) Alemany, Kristina ; Braun, Robert D.

In 2006, the 2nd Global Trajectory Optimization Competition (GTOC2) posed a “Grand Asteroid Tour” trajectory optimization problem, where participants were required to find the best possible low-thrust trajectory that would rendezvous with one asteroid from each of four defined groups. As a first step, most teams employed some form of design space pruning, in order to reduce the overall number of possible asteroid combinations. Because of the large size of the problem, teams were not able to determine if their pruning technique had successfully eliminated only bad solutions from the design space. Therefore, a small subset of the GTOC2 problem was analyzed, and several design space pruning techniques were applied to determine their effectiveness. The results indicate that the pruning techniques chosen by the participants likely eliminated good solutions from the design space, because they either did not accurately represent the low-thrust problem or could not be considered independently without the effect of other factors.
An Approach for Calculating the Cost of Launch Vehicle Reliability

(Georgia Institute of Technology, 2007-09) Krevor, Zachary C. ; Wilhite, Alan W.

The goal of this paper is to determine the cost of increasing launch vehicle reliability during conceptual design. The launch vehicle mission requirements are held constant while various reliability strategies are evaluated for their affects on different performance and cost metrics. Traditional design disciplines, such as trajectory analysis and propulsion are included within the performance analysis while the cost discipline focuses on launch vehicle development and production cost. The reliability modeling is developed specifically for application to launch vehicles. A design environment is created that integrates the performance, cost, and reliability disciplines for use with optimization. The integrated environment is utilized to determine a set of optimal design configurations based on a specific weighting of cost and reliability. Different design options for the Cargo Launch Vehicle from the Exploration System Architecture Study are considered and the final result is a set of configurations optimized for a particular weighting of cost and reliability.
Mars Gravity Biosatellite: Engineering, Science, and Education

(Georgia Institute of Technology, 2007-09) Korzun, Ashley M. ; Braun, Robert D. ; Wagner, Erika B. ; Fulford-Jones, Thaddeus R.F. ; Deems, Elizabeth C. ; Judnick, Daniel C. ; Keesee, John E.

The Mars Gravity Biosatellite is a novel program aimed at providing data on the effects of partial gravity on mammalian physiology. Physiological problems intrinsic to prolonged stays in microgravity have long been concerns of manned spaceflight and will continue to be a significant obstacle in achieving the goals outlined in NASA’s Vision for Space Exploration. This student-developed, free-flyer spacecraft is designed to carry a payload of 15 mice into low Earth orbit, rotating to generate an acceleration environment equivalent to Martian gravity. After 35 days, the payload will be de-orbited and recovered for study. Data collected during the mission and post-recovery will be used to characterize the physiological changes incurred under partial gravity conditions and validate the models used in designing the spacecraft. This paper presents the preliminary design of the spacecraft. By providing groundbreaking flight data on the effects of partial gravity on mammalian physiology and engaging over 500 students to date, the Mars Gravity Biosatellite program is working to enable successful human exploration of the Moon and Mars while training and inspiring a new generation of scientists and engineers.