Alan Wilhite

Alan Wilhite
Georgia Institute of Technology | GT · School of Aerospace Engineering

PhD, Aerospace Engineering, North Carolina State University, 1984

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119
Publications
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582
Citations

Publications

Publications (119)
Article
Full-text available
Systems enabling long-duration crewed missions are expected to have high probabilities of success through sparing of components. To enable such systems, the tradeoff between the reliability and the mass needs to be incorporated early in the design phase to ensure that the requirements are optimally captured. Additionally, effective operational spar...
Article
Full-text available
This study’s primary purpose was to assess the feasibility of new approaches for achieving our national goals in space. NexGen assembled a team of former NASA executives and engineers who assessed the economic and technical viability of an “Evolvable Lunar Architecture” (ELA) that leverages commercial capabilities and services that are existing or...
Article
Full-text available
A case study is presented on risk management as applied to the development of advanced technologies. The success of complex projects depends on the parallel development and integration of diverse technologies. Prior to investing large sums of money in these technologies, stakeholders want to know the risk in technology investment that includes the...
Conference Paper
Withincreased interest in paradigm-shifting aerospace vehicles, such as those with a blended wing-body configuration or mostly composite structures, it is necessary to develop structural design methods that will help these concepts reach their full potential. With the introduction of advanced vehicle geometry and materials, the dimensionality of th...
Article
In any manned mission architecture, upwards of seventy percent of all payload delivered to orbit is propellant, and propellant mass fraction dominates almost all transportation segments of any mission requiring a heavy lift launch system like the Saturn V. To mitigate this, the use of an orbital propellant depot has been extensively studied. In thi...
Article
Current space system architecture modeling frameworks use a variety of methods to generate their architecture definitions and system models but are either too manual or too limited in scope to effectively explore the architecture-level design space exploration. This paper outlines a method to mathematically model space system architectures using gr...
Article
NASA has created a plan to implement the Flexible Path strategy, which utilizes a heavy lift launch vehicle to deliver crew and cargo to orbit. In this plan, NASA would develop much of the transportation architecture (launch vehicle, crew capsule, and in-space propulsion), leaving the other in-space elements open to commercial and international par...
Article
With increased interest in paradigm-shifting aerospace vehicles, such as those with a blended wing-body configuration or mostly composite structures, it is necessary to develop structural design methods that will help these concepts reach their full potential. Many traditional design methods are only suited for traditional aerospace structures. Wit...
Conference Paper
The objective of space habitat design is to minimize mass and system size while providing adequate space for all necessary equipment and a functional layout that supports crew health and productivity. Unfortunately, development and evaluation of interior layouts is often ignored during conceptual design because of the subjectivity and long times re...
Conference Paper
The use of orbital depots for cryogenic propellants has become a prominent concept for enabling large-scale deep space exploration missions with high propellant requirements. Propellant depots are intended to eliminate the need for a heavy-lift launch vehicle, but lack the flight history of heavy-lift launch vehicles. As such, it is necessary to th...
Conference Paper
Full-text available
Preinjection of fuel on the forebody of an airbreathing vehicle is a proposed method to gain access to hypervelocity flight Mach numbers. However, this creates the possibility of autoignition either near the wall or in the core of the flow, thereby consuming fuel prematurely as well as increasing the amount of pressure drag on the vehicle. The comp...
Article
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A crewed mission to a near earth asteroid would yield both scientific and engineering advancements. Visiting one or several of these objects would not only validate technologies that could later be used to visit the Moon or Mars, but would also develop our scientific understanding of asteroids and the solar system. This study proposes an architectu...
Article
Habitable volume is an important spacecraft design figure of merit necessary to determine the required size of crewed space vehicles, or habitats. In order to design habitats for future missions and properly compare the habitable volumes of future habitat designs with historical spacecraft, consistent methods of both defining the required amount of...
Conference Paper
The 2010 National Space Policy set wide reaching goals for the United States space pro- gram, however these milestones are in serious jeopardy due the economic down turn and budget restrictions. There is an increasing need to examine the current exploration archi- tecture to determine if there are more economical, yet still technically feasible opt...
Conference Paper
Full-text available
The use of premixed, shock-induced combustion in the context of a hypervelocity, airbreathing vehicle requires effective injection and mixing of hydrogen fuel and air on the vehicle forebody. Three dimensional computational simulations of fuel injection and mixing from flush-wall and modified ramp and strut injectors are reported in this study. A w...
Article
The abstract presents concepts and approaches for the reduction of uncertainty in radiation exposure estimation. Radiation presents a major challenge for human exploration of Mars and some risk could be mitigated through less uncertainty.
Conference Paper
Full-text available
Rocket vehicles today are limited by the chemical potential of their propellants, regardless of advancements in combustion technology or engine and nozzle material properties. Increasing specific impulse for high thrust levels would widen the spectrum of technically feasible space mission architectures. Current LH2-fueled nuclear thermal engine des...
Conference Paper
In order to make long duration human space exploration feasible, significant advances must be made to overcome current technology limitations. In any manned mission architecture, upwards of seventy percent of all payload delivered to orbit is propellant and propellant mass fraction dominates almost all segments of any mission due to the current lim...
Conference Paper
Full-text available
Recent studies indicate a significant need for increased remediation efforts of the low Earth orbit (LEO) debris environment. Without active debris removal (ADR), the LEO debris population will grow at an ever-increasing rate, eventually preventing any form of sustainable space operations. Based on evolutionary debris field simulations from the lit...
Conference Paper
Radiation environments beyond low Earth orbit represent a serious risk to crew health and, as a result, mission success. Often, this hazard is not adequately addressed in the conceptual phase of architecture modeling and evaluation. This situation can lead to candidate designs that inadequately mitigate crew needs related to radiation protection an...
Conference Paper
Full-text available
A premixed, shock-induced combustion engine has been proposed in the past as a viable option for operating in the Mach 10 to 15 range in a single stage to orbit vehicle. In this approach, a shock is used to initiate combustion in a premixed fuel/air mixture. Apparent advantages over a conventional scramjet engine include a shorter combustor that, i...
Conference Paper
As the cost and complexity of deep space missions continue to climb, the interaction of spacecraft with highly dynamic atmospheric environments will increase in frequency. Uncertainty in atmospheric state estimates leads to an increase in both mission risk and the trajectory and design margins required to ensure safe atmospheric entry. Algorithms f...
Conference Paper
The wing/body design of reusable launch vehicles must meet the aerodynamic constraints through the complete speed regime from hypersonic entry to subsonic landing. In order to investigate a complete range of wing and body shapes, parametric geometry models were developed and integrated with the Aerodynamic Preliminary Analysis System (APAS) to perf...
Conference Paper
With the release of the Design Reference Architecture 5.0, NASA established a new baseline for crewed missions to Mars. The most notable change in this iteration is the chemical propulsion option for the trans-Mars injection and Mars orbit insertion mission phases as an alternative to the baseline nuclear thermal propulsion option in previous versi...
Conference Paper
Mass growth in aerospace systems from conceptual design to first flight is a well known issue. The substantial mass growth is attributed to requirements changes, uncertainty in the performance of the technology, and uncertainty in the mass estimation of the different subsystems. Historical aerospace systems show an average of 28.5 percent mass grow...
Conference Paper
The selection of a space system architecture to perform a human space mission is the most important decision in the development process. This decision provides the greatest impact on the cost and performance of the mission. However, decisions not only affect the current mission, but also subsequent missions in the overall exploration program. This...
Conference Paper
This paper develops a design methodology for future planetary habitat interior layouts and proposes a preliminary approach for optimization. The purpose of this paper is two-fold. The first purpose is to outline a structured methodology to perform systems level evaluations of habitat interior layouts. This process uses multi-attribute decision maki...
Article
Inert or dry mass in aerospace systems has historically grown during aerospace vehicle development because of a number of factors: changing requirements, uncertainty in the performance of the initial technology selection, addition of redundancy, errors in the original design, as well as uncertain masses and loads. In the case of exploration archite...
Article
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 perform...
Article
Many human lunar exploration architectures, both flown and conceptual, use at least one heavy-lift launch vehicle to deliver flight hardware to low Earth orbit. There exists a technology, however, that allows these large exploration missions to be performed without the use of a heavy-lift launch vehicle: propellant transfer. This study presents a m...
Article
Full-text available
This paper presents an analysis of the ascent stage to be used in future human missions to Mars, commonly known as the Mars Ascent Vehicle. The focus of the analysis is to minimize the initial mass, which must be delivered to low-Earth orbit to have a fully functioning Mars Ascent Vehicle. At the end of the surface mission, the Mars Ascent Vehicle...
Article
The performance, cost, and safety benefits of developing a variety of revolutionary technologies for inclusion in crewed Mars missions are quantified. Technologies in propulsion and materials are investigated individually and in various combinations with respect to their effects on overall mission economic and safety figures of merit. These technol...
Article
Parallel coordinates plot (PCP) for visualization of multidimensional human interplanetary mission design space was proposed. The heliocentric trajectories were calculated using the universal variable solution to Lambert's problem to generate the data set used in this technique. The positions of the planets were obtained from the planetary ephemeri...
Conference Paper
This paper outlines a methodology to mathematically model space architectures by using graph theory. An overview of previous Mars architecture design studies is given, from the early studies in the Apollo era to the Space Exploration Initiative to the latest Design Reference Architecture 5.0. Utilizing graph theory to model architectures provides a...
Conference Paper
Full-text available
To support a permanent human settlement on the Lunar surface, improvements to the current Lunar outpost architecture are investigated. A detailed analysis of architectures utilizing an orbital propellant depot and reusable vehicles is presented. Comparisons focus on cost, extensibility, performance, heritage, and reliability. An architecture utiliz...
Conference Paper
Full-text available
The purpose of this paper is to perform a preliminary comparative analysis of four leading bimodal nuclear thermal propulsion system designs to determine which would result in the lowest initial mass in low-Earth orbit and how it would affect Mars mission payload capability and a launch vehicle's lift requirement. The Commonwealth of Independent St...
Conference Paper
Full-text available
§An aeroelastic analysis of the behavior of an entry vehicle utilizing an attached inflatable aerodynamic decelerator during supersonic flight is presented. The analysis consists of a planar, four degree of freedom simulation. The aeroshell and the IAD are assumed to be separate, rigid bodies connected with a spring-damper at an interface point con...
Article
This study is to find an optimized architecture for transporting crew and cargo vehicle to the moon and return. The mission requires the following burns: low-Earth orbit insertion, translunar injection, lunar orbit insertion, lunar descent, lunar ascent, and transEarth injection. Apollo and the present architecture both have four stages. The presen...
Article
Various lunar descent trajectories were analyzed that include the optimization of the Apollo constrained mission trajectory, a fully optimized minimum energy trajectory, and a optimal, constrained trajectory using current instrumentation technology. Trade studies were conducted to determine the impacts of mission assumptions, pilot in the loop/auto...
Article
A process was developed for determining the impact of technology performance assumptions and weight prediction method uncertainty. Weight and performance uncertainties were defined for components from historical weight-estimating relationships that are typically used during the concept definition phase. A systems analysis model was developed that s...
Article
Full-text available
AIAA SPACE 2007 Conference & Exposition 18-20 September 2007, Long Beach, California. 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 performan...
Article
Full-text available
The conceptual design of an architecture for space exploration involves the evaluation of many concepts. These design spaces may encompass millions or billions of options when each trade is evaluated at the system, vehicle, subsystem, and component level. Various techniques are typically employed to select the conf iguration of systems that best me...
Article
A new method for selecting the number of engines on a rocket stage based upon re- liability and cost is presented. This method will compare a new technique for reliability analysis that results in a higher fidelity model when considering engine out capability. The cost of each vehicle configuration is calculated to find an optimal balance of system...
Article
Full-text available
In January 2005, President Bush announced the Vision for Space Exploration. This vision involved a progressive expansion of human capabilities beyond Low Earth Orbit beginning with a return to the moon starting no later than 2020. Current design processes utilized to meet this vision employ performance based trade studies to determine the lowest co...
Article
14th AIAA/AHI Space Planes and Hypersonic Systems and Technologies Conference November 2006, Canberra, Australia Lazarus is an unmanned single stage reusable launch vehicle concept utilizing advanced propulsion concepts such as rocket based combined cycle engine (RBCC) and high energy density material (HEDM) propellants. These advanced propulsion e...
Conference Paper
This article develops and presents a technology engineering framework for the selection, development, and insertion of space transportation technologies concurrent with the systems engineering of the space transportation system(s) in which the technology will eventually be employed. The technology engineering framework developed and presented in th...
Article
Full-text available
AIAA Space 2006 Conference September 2006, San Jose, CA.
Article
This conference features the work of authors from: Georgia Tech’s Space Systems Design Lab, Aerospace Systems Design Lab, School of Aerospace Engineering, Georgia Tech Research Institute; NASA’s Jet Propulsion Laboratory, Marshall Space Flight Center, Goddard Space Flight Center, Langley Research Center; and other aerospace industry and academic in...
Article
A viewgraph presentation on the cost/risk analysis capability of systems engineering is shown.
Article
Full-text available
The approach and techniques described herein define an optimization and evaluation approach for a liquid hydrogen/liquid oxygen single-stage-to-orbit system. The method uses Monte Carlo simulations, genetic algorithm solvers, a propulsion thermo-chemical code, power series regression curves for historical data, and statistical models in order to op...
Article
GT-SSEC.E.4 First Annual Space Systems Engineering Conference November 2005, Atlanta, GA. The crew launch vehicle is a new NASA launch vehicle design proposed by the Exploration Systems Architecture Study (ESAS) to provide reliable transportations of humans and cargo from the earth’s surface to low earth orbit (LEO). ESAS was charged with the task...
Article
One of the challenges facing the designers of an integrated engineering system is to blend in a robust and efficient way a wide variety of independently developed programs, each with its specific requirements for input and output. The Environment for Application Software Integration and Execution (EASIE, for short) provides a methodology and set of...
Article
Horizontal takeoff and landing two-stage systems with an airbreathing first stage and rocket second stage are evaluated for staging Mach numbers that range from 5 to 14. All systems are evaluated with advanced technologies being developed in the NASP Program and sized to the same mission requirements. With these advanced technologies, the two-stage...
Article
Various concepts for advanced manned launch systems (AMLS) are examined for delivery missions to Space Station and polar orbit. Included are single- and two-stage winged systems with rocket and/or airbreathing propulsion systems. For near-term technologies, two-stage, reusable rocket systems are favored over single-stage rocket or airbreathing/rock...
Article
In this paper a predominantly airbreathing SSTO vehicle is compared with three different TSTO configurations that stage at Mach numbers of 10, 12, and 14. The first stage of the TSTO vehicle uses the same propulsion system type and airframe shape as the SSTO vehicle except for modifications required to integrate the orbiter on top of the first stag...
Article
A predominantly airbreathing SSTO vehicle is compared with three different two stages to orbit (TSTO) configurations which stage at Mach numbers 10, 12, and 14. The technologies utilized on each of the vehicles are consistent with a successful NASP technology development program in the areas of structures, propulsion systems, and subsystems. To det...