Alan Wilhite

Design options for advanced manned launch systems

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 two-stage airbreathing/rocket systems. Advanced technologies enable viable single-stage-to-orbit (SSTO) concepts. Although two-stage rocket systems continue to be lighter in dry weight than SSTOs, advantages in simpler operations may make SSTOs more cost effective over the life cycle. Generally, rocket systems maintain a dry weight advantage over airbreathing systems at the advanced technology levels, but to a lesser degree than when near-term technologies are used. More detailed understanding of vehicle systems and associated ground and flight operations requirements and procedures is essential in determining quantitative discrimination between these latter concepts.

Prediction of high-speed aerodynamic characteristics using the Aerodynamic Preliminary Analysis System (APAS)

An exercise was performed which illustrates the prediction of high-speed aerodynamic coefficients using the Aerodynamic Preliminary Analysis System. Two generic transatmospheric vehicle configurations are used as examples on which various inviscid and viscous estimation techniques are applied. As a means of evaluating the reliability of the Aerodynamic Preliminary Analysis System results, comparisons of predictions using this preliminary-level approach are compared with Shuttle-derived data, hypersonic helium tunnel data for several configurations, and computational fluid dynamics results. Overall, predictions using the Aerodynamic Preliminary Analysis System agree well with the other calculations and data.

Estimating the Risk of Technology Development

Abstract: 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 probability of technology development success and the impact the technology would have on the system. The risk identification process consists of developing the functional and technology needs of the system; collecting data on potential technology solutions; assessing the technology development probability of success for performance, cost, and schedule; determining the impact of the technology on the programs; and developing decision analysis presentations for the stakeholders. Based on a modified analytical hierarchical process, the Internet-Accessible Technology Risk Assessment Collaborative System (ITRACS©) was developed to solicit opinions from experts across the nation for the technology probability of success assessment. In addition, the Framework for Advanced Systems Trade-offs using Probabilistic Analysis of Concepts and Technologies (FASTPACT©) environment was developed to determine the technology impact on the system as measured by program Figures of Merit (FOMs)—safety, cost, and weight. The results from this technology analysis showed that many of the technologies in the present technology investment portfolio were not very effective in impacting the program FOMs, and that in some cases, multiple technologies in the same area should be funded to improve probability of development success.

Orbital Propellant Depots Enabling Lunar Architectures Without Heavy-Lift Launch Vehicles

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 methodology to incorporate propellant transfer into conceptual design of lunar architectures through the use of a low-Earth-orbit propellant depot. This technology is then applied to a two-launch human lunar architecture without a heavy-lift launch vehicle. The results show that not only is a lunar architecture without a heavy-lift launch vehicle feasible with a propellant depot, but it can also improve the capability to deliver payload to the surface over an architecture that includes a heavy-lift launch vehicle without a propellant depot. The optimal lunar lander for this architecture is a hypergolic lander with a deck height of only 1.53meters that performs only a portion of the descent burn, while the trans-lunar injection stage performs the other portion. The hypergolic propellant allows for a simpler, less expensive propulsion system, a volumetrically smaller lander, and enables the use of the existing hypergolic propellant transfer technology.

Modeling Space System Architectures with Graph Theory

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 graph theory, which provides a simple mathematical framework that is flexible enough to model many different system architecture options, such as lunar, asteroid, and Mars missions. Multiple lunar system architectures were considered in NASA’s Exploration System Architecture Study mission modes comparison. These system architectures are modeled within this framework to demonstrate the ability to rapidly compare the performance of different system architectures within a single framework. This capability is crucial in order to explore the system architecture-level design space and make informed decisions on the future of a human space exploration program.

Technology and staging effects on two-stage-to-orbit systems

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 systems are heavier than the single stage. The weights of the two-stage systems are closely related to staging. Using a rocket on the first stage to accelerate from the turboramjet limit of Mach 6 to Mach 10 signiificantly decreases dry weight as compared to the Mach 6-staged system. The optimum dry weight staging Mach number for the scramjet two-stage system is Mach 12. At a 40 percent weight growth (current technology level), the scramjet two-stage systems are half the weight and less sensitive to weight changes than the single stage, but still require substantial technology development in the areas of inlets, nozzles, ramjet propulsion, active cooling, and high-temperature structures.

Architecture Options for Propellant Resupply of Lunar Exploration Elements

The NASA Exploration Systems Architecture Study (ESAS) 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 resupply available, there is the potential to increase the payload that can be put on the moon, increase lunar mission durations, and enable a wider range of lunar missions. The availability of on-orbit cryogenic propellants, either at a propellant depot or directly from a propellant transfer stage, would impact the sizing and reusability of many architecture elements, including the Earth Departure Stage (EDS), the Crew Launch Vehicle (CLV) upper stage, the Lunar Surface Access Module (LSAM), and the Service Module (SM). These vehicles are modeled to approximate the baseline established by ESAS. Methods and tools used include launch trajectory optimization with POST, vehicle aerodynamic analysis using APAS, weights and sizing using historical and physics based estimating relationships, and cost estimation using NAFCOM. Uncertainty in estimates of advanced technology performance is modeled using probabilistic methods, such as Monte Carlo simulation. The impact of propellant resupply capability on vehicle design and performance is investigated. The availability of propellant at LEO allows for many possible architecture changes, including increasing the payload delivered to the moon, decreasing the size of the heavy lift launch vehicle, or staging extra propellant in lunar orbit. Other elements could also be designed to be reusable with propellant resupply available, such as the LSAM, the CLV upper stage, and the Service Module. Several of these architecture changes are investigated, and compared via metrics such as mission reliability, cost, and the range of lunar and near-Earth mission capabilities (i.e. duration time, mission latitude, missions to Lagrange points) they allow.

Lazarus: A SSTO Hypersonic Vehicle Concept Utilizing RBCC and HEDM Propulsion Technologies

14th AIAA/AHI Space Planes and Hypersonic Systems and Technologies Conference November 2006, Canberra, Australia

Study of Forebody Injection and Mixing with Application to Hypervelocity Airbreathing Propulsion

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 well-established code, VULCAN, is used to conduct nonreacting, viscous, turbulent simulations on a flat plate at conditions relevant to a Mach 12 flight vehicle forebody. In comparing results of various fuel injection strategies, it is found that strut injection provides the greatest balance of performance between mixing efficiency and stream thrust potential.

Reusable Lunar Transportation Architecture Utilizing Orbital Propellant Depots

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 utilizing a two stage reusable transit vehicle, a reusable Lunar lander, and a integrated orbital propellant depot is proposed. A 30% reduction in cost for payload delivered to the lunar surface is achieved with the proposed architecture when compared to the ESAS architecture. A detailed breakdown of the architecture is presented and recommendations are made regarding the direction of technology investments needed to enable permanent human settlement on the Lunar surface.