Design Trade Studies Research Articles

Superconducting Ducted Fan Design for Reduced Emissions Aeropropulsion

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This article introduces a new conceptual design tool for an environmentally sustainable method of aeropropulsion: a ducted fan system driven by a fully superconducting electrical machine. Such a system could help mitigate aviation's contribution to global climate change by enabling the reduction of greenhouse gas emissions from aircraft. An electro-thermal motor sizing model was coupled with cycle analysis and weight estimation routines to create an automated environment for rapid design trade studies. The resulting parametric cycle analysis and sizing outcomes revealed the system's operational boundaries for a given aspiration space. </para>

Recent progress at NASA in LISA formulation and technology development

Over the last year, the NASA half of the joint LISA project has focused its efforts on responding to a major review, and advancing the formulation and technology development of the mission. The NAS/NRC Beyond Einstein program assessment review will be described, including the outcome. The basis of the LISA science requirements has changed from detection determined by integrated signal-to-noise ratio to observation determined by uncertainty in the estimation of astrophysical source parameters. The NASA team has further defined the spacecraft bus design, participated in many design trade studies and advanced the requirements flow down and the associated current best estimates of performance. Recent progress in technology development is also summarized.

Adaptive optics sky coverage modeling for extremely large telescopes

A Monte Carlo sky coverage model for laser guide star adaptive optics systems was proposed by Clare and Ellerbroek [J. Opt. Soc. Am. A 23, 418 (2006)]. We refine the model to include (i) natural guide star (NGS) statistics using published star count models, (ii) noise on the NGS measurements, (iii) the effect of telescope wind shake, (iv) a model for how the Strehl and hence NGS wavefront sensor measurement noise varies across the field, (v) the focus error due to imperfectly tracking the range to the sodium layer, (vi) the mechanical bandwidths of the tip-tilt (TT) stage and deformable mirror actuators, and (vii) temporal filtering of the NGS measurements to balance errors due to noise and servo lag. From this model, we are able to generate a TT error budget for the Thirty Meter Telescope facility narrow-field infrared adaptive optics system (NFIRAOS) and perform several design trade studies. With the current NFIRAOS design, the median TT error at the galactic pole with median seeing is calculated to be 65 nm or 1.8 mas rms.

The Optical Telescope Assembly for the Terrestrial Planet Finder Coronagraph: Design and Analysis Results

The Terrestrial Planet Finder Coronagraph (TPFC) is a National Aeronautics and Space Administration (NASA) exploration mission to directly detect and characterize terrestrial exoplanets at visible and near-infrared wavelengths. The TPFC mission is currently in a “pre-formulation” stage where requirements and designs are traded. TPFC must distinguish a planet that is more than 10 orders of magnitude fainter than its parent star at a separation of 62 mas ( nm). Coronagraphic detection requires a large aperture telescope to resolve the exoplanet from its parent star, and great system (wavefront) stability during detection and characterization. This paper discusses the design considerations, trade studies and analysis leading to the current, “reference” design for the TPFC telescope. We present the salient features of the design and the most significant structural, thermal and optical analysis results. We also discuss the planned model validation and performance verification approach.

Space systems considerations in the design of advanced geostationary operational environmental satellites

Advances in space systems are providing challenging opportunities for the design of smaller, lighter, more efficient and cheaper satellite systems. A review of spacecraft power systems, structural materials, thermal design and cooling systems, electronic modules and advances in detector technology is provided. The science requirements for NOAA's advanced imager are presented. The NASA Jet Propulsion Laboratory design trade study for NOAA's 8-channel advanced imager shows that a 30 cm aperture mirror design can meet most of NOAA's requirements; though superior, the 45 cm mirror design option was abandoned due to instrument mass restrictions. The Aerospace Corporation was requested by NOAA to compare consolidated and distributed architectures. There appears to be no significant advantage for NOAA in pursuing distributed architecture for our future systems. A lighter overall mass is the key driver in reducing geostationary launch vehicle costs. Instrument design trade studies and spacecraft architectural studies are helping NOAA to plan for the future GOES systems.

Mixer-Ejector Noise-Suppressor Model

A flexible and efficient compressible mixer-ejector model is described. This model is used to predict the performance of ejectors employing lobed mixers. Through comparisons with experimental data, the model is shown to qualitatively capture the impact of streamwise vorticity on the evolution of the mixing layer and to quantitatively predict the change in the pressure coefficient through the duct associated with the mixing process to within 15 %. The relative accuracy, speed, and flexibility of the model make it useful as a preliminary design tool. Two design trade studies are performed with the model. First, the model is used to assess the impact of streamwise vorticity on the thrust and pumping performance of a supersonicsubsonic mixer-ejector; for the mixer geometry utilized in this study, pumping and thrust augmentations are associated with the addition of streamwise vorticity. Second, the impact of mixer height on the effectiveness of streamwise vorticity is evaluated. The results of this study demonstrate that the effectiveness of streamwise vorticity decreases with increasing lobe height-to-wavelength ratio, and for the higher height-to-wavelength ratios investigated, a net performance penalty is associated with the addition of streamwise vorticity.

Parametric cost model for solar space power and DIPS systems

A detailed cost model has been developed to parametrically determine the program development and production cost of photovoltaic, solar dynamic, and dynamic isotope (DIPS) space power systems. The model is applicable in the net electrical power range of 3 to 300 kWe for solar power and 0.5 to 10 kWe for DIPS. Application of the cost model allows spacecraft or space-based power system architecture and design trade studies or budgetary forecasting and cost benefit analyses. The cost model considers all major power subsystems (i.e., power generation, power conversion, energy storage, thermal management, and power management/distribution/control). It also considers system cost effects such as integration, testing, and management. The cost breakdown structure, model assumptions, ground rules, bases, cost estimation relationship format, and rationale are presented, and the application of the cost model to 100-kWe solar space power plants and to a 1.0-kWe DIPS is demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Functional Requirement Mapping as a Framework for Concurrent Engineering

The complexity of current engineered products has created an environment of information overload for the personnel responsible for the many stages of product engineering and development. The increasingly competitive global market has created an added demand for shorter design and production cycles. This paper will examine a technique described as functional requirement mapping (FRM) as a flexible framework for organizing a comparative design process or trade study. An organized design process is one characterized by the ability to structure hybrid sets of information which define results of current design efforts, future tasks and their priority, various metrics, and a presentation format for decision making. A number of current concepts will be addressed within the scope of this topic, including axiomatic design theory and object-oriented paradigms of software engineering. An example case will be used to illustrate the concepts presented in this paper. The contribution of this paper will be the presentation of a theoretical basis and prototype model for development of a concurrent engineering software application.

Durability Assessment Based on Initial Material Quality

Abstract New U.S. Air Force durability design philosophies are aimed at minimizing evolution and growth of structural cracks to sizes affecting readiness and life cycle repair costs. Durability design requires attention to material quality and manufacturing quality, since both can be sources of in-service cracking problems. Improvement in the quality of Al-Zn-Cu-Mg, 7050 alloy, thick plate through reductions in microporosity has been correlated with increased smooth-coupon fatigue lives. Consequently, in commercial production, the smooth fatigue test is now employed as a lot release test to warrant initial metal quality. This work is aimed at translating results of smooth fatigue quality-screening tests to aircraft component performance in the context of new durability methodologies. For this purpose, a fracture mechanics analysis is used to convert the smooth coupon lifetimes to an equivalent initial flaw size (EIFS) distribution, which then becomes the starting point for probabilistic crack growth assessment in a component. The EIFS distribution back-extrapolated from life data is shown to be in good agreement with the distribution of crack initiating microflaws determined by more labor-intensive post-test fractography. Consequently, the fracture mechanics back-calculation enables cost-effective conversion of coupon lifetimes, a simple measurement, into a “material characteristic,” initial flaw size population, which can then be utilized analytically for durability design trade studies. A hypothetical component study performed in this manner for materials of varying initial quality is used to demonstrate how material quality differentiated at the coupon level can be translated into a performance advantage under representative in-service loading conditions.

Elevated temperature aluminum alloys for advanced fighter aircraft

Elevated temperature aluminum alloys are being developed for aircraft structural applications in the 300 F to 600 F temperature range. Material properties of various alloy systems and product forms display excellent room and elevated temperature strength, fracture toughness, and corrosion resistance. These materials are considered for applications in the aft fuselage of an Advanced Tactical Fighter (ATF). Design trade studies were conducted for a center keel beam structure between the engine compartments. Results show potential weight and cost savings of 12.8 percent and 46.5 percent, respectively, for a structure fabricated from elevated temperature aluminum alloys as opposed to titanium alloys. Additional weight and cost savings can be achieved by using hot molded metal matrix composite (MMC) Al/SiCf beam caps.

Low-cost composite primary structure : Lloyd, M.S., O'Brien, W.L. and Parker, D.E. SAMPE Quarterly Vol 9 No 1 (October 1977) pp 28–39

The B-1 vertical stabilizer has been redesigned taking advantage of the unique properties of advanced composite materials to realize weight as well as cost savings. The advanced composite vertical stabilizer has been designed to meet all of the physical and functional-interfaces as well as the service environment. The more significant design trade studies leading to selection of the final structural configuration and testing to verify structural integrity are discussed. Evolution of the tooling required to fabricate the advanced composite substructure is presented, beginning with the original concept and rationale for selection. Various refinements which have been initiated either to improve the producibility of the composite parts or increase the longevity of the tooling are also discussed.

Human Resources Data in System Design Trade Studies

The system design trade study process was investigated to determine the feasibility of including human resources data. First, 61 completed trade studies from aeronautical, missile, and command and control systems were analyzed to determine the characteristics of trade studies. Then, four simulated trade studies containing engineering and human resources data and representing flight control and avionics subsystems were constructed for experimental use. Seventy-two experienced design engineers performed the simulated trade studies. It was found that engineers can and do use human resources data in system design trade studies. Personnel costs and quantities are assigned more weight than skill types, skill levels, and availability of personnel. A detailed presentation of human resources data is given more weight than a condensed presentation. Four major sources of variability in trade study results were found. These are: choice of parameters, weighting factors for the parameters, methods of normalizing the parametric data, and methods of combining parametric data and weighting factors. Standardization of trade study methods is recommended to help overcome this variability.

Reliability considerations in design trade studies : R. L. Eisner. Proc. Ann. Symp. Reliab., Washington D.C., U.S.A., IEEE Cat. No. 71C 2-R, 12–14 January (1971), p. 98

Reliability considerations in design trade studies : R. L. Eisner. Proc. Ann. Symp. Reliab., Washington D.C., U.S.A., IEEE Cat. No. 71C 2-R, 12–14 January (1971), p. 98