Design Trade Studies Research Articles

Setting the Stage for the Search for Life with the Habitable Worlds Observatory: Properties of 164 Promising Planet-survey Targets

The Decadal Survey on Astronomy and Astrophysics 2020 has recommended that NASA realize a large IR/optical/UV space telescope optimized for high-contrast imaging and spectroscopy of ∼25 exo-Earths and transformative general astrophysics. The NASA Exoplanet Exploration Program (ExEP) has subsequently released a list of 164 nearby (d < 25 pc) targets deemed the most accessible to survey for potentially habitable exoplanets with the Habitable Worlds Observatory (HWO). We present a catalog of system properties for the 164 ExEP targets, including 1744 abundance measurements for 14 elements from the Hypatia Catalog and 924 photometry measurements spanning from 151.6 nm to 22 μm in the GALEX, Strömgren, Tycho, Gaia, Two Micron All Sky Survey, and Wide-field Infrared Survey Explorer bandpasses. We independently derive stellar properties for these systems by modeling their spectral energy distributions with Bayesian model averaging. Additionally, by consulting the literature, we identify TESS flare rates for 46 stars, optical variability for 78 stars, and X-ray emission for 46 stars in our sample. We discuss our catalog in the context of planet habitability and draw attention to key gaps in our knowledge where precursor science can help to inform HWO mission design trade studies in the near future. Notably, only 33 of the 164 stars in our sample have reliable space-based UV measurements, and only 40 have a mid-IR measurement. We also find that phosphorus, a bioessential element, has only been measured in 11 of these stars, motivating future abundance surveys. Our catalog is publicly available and we advocate for its use in future studies of promising HWO targets.

Analyzing Micrometeoroid and Orbital Debris Shield Performance for Sample Return Spacecraft

Sample-return missions typically seek to collect and return samples from extraterrestrial locations to Earth for analysis. The return of samples from certain locations in the solar system represents a potential hazard to Earth’s biosphere from foreign microorganisms. One way this could occur would be a break-up of the returning capsule during entry (which would disperse the samples through the air) due to undetected damage to the capsule thermal protection system (TPS). As a result, missions that plan to return payloads from some destinations are likely to have certain design requirements for the TPS surrounding their returning capsules, which may include ensuring that the TPS shielding is able to withstand damage due to micrometeoroid and orbital debris impacts. In this paper, we develop a particle impact-based ballistic limit equation (BLE) for a shielded TPS covering a variety of impact scenarios, as well as shield component materials, thicknesses, and internal spacings. The predictions of the BLE we develop with regard to TPS failure/nonfailure are seen to be consistent with the predictions of hydrocode simulations. Because of the manner in which it was developed, the BLE is sufficiently flexible that it can be used for design trade studies and probabilistic risk assessment exercises.

Sizing of Superconducting Cables for Turbo-ElectricDistributed Propulsion Aircraft Using a Particle Swarm Optimization Approach

Superconducting electrical power systems are proposed to meet high specific power densities required for turbo-electric distributed propulsion aircraft. Superconducting materials have unique thermal and electrical requirements for maintaining the superconducting state, which is critical to their normal operation. Electrical system faults can lead to this state being lost for all network assets in the electrical fault path. The resulting temperature rise can prevent the superconducting state from being immediately resumed following fault clearance, requiring disconnection of nonfaulted equipment. Undersized cables experience a higher temperature rise under faulted conditions and disconnect from the system more readily. Oversized cables are heavier and more costly. Therefore, there is a need to optimize the cable size, preventing disconnection of equipment due to temperature rise following a fault while minimizing the weight and cost penalty. This article proposes a system parameter-driven methodology, using particle swarm optimization, to identify fault-tolerant cable designs, which deliver minimum through-life costs. This facilitates high-value, quantifiable design trade studies incorporating system parameters. Key observations drawn are that the choice between improving fault ride-through capability of a superconducting cable by increasing the amount of either superconducting material or conventional former material strongly depends on acceptable system operating temperature and voltage.

Combined Momentum Theory and Simple Vortex Theory Inflow Model for Multirotor Configurations

For conventional main/tail rotor helicopters, momentum theory-based inflow models are still popular for design trade studies and flight simulations. However, simple momentum theory-based inflow models are not readily applicable in design trade studies of multirotor configuration vehicles where complex flow interactions among rotors can have a significant impact on vehicle overall performance, and hence, can impact vehicle sizing. The use of empirically corrected ad hoc inflow models is not often satisfactory. In this study, momentum theory is combined with a simple vortex theory in the development of a combined momentum theory and simple vortex theory (CMTSVT) based inflow model that is readily applicable to generic multirotor configurations. The developed model is validated against some multirotor inflow models and experimental data from the literature through comparisons of inflow predictions and performance predictions for different dual-rotor configurations. Further, inflow predictions using the proposed inflow model for a partially overlapping quad-rotor configuration are presented to illustrate the significance of rotor-on-rotor flow interactions in multirotor vehicle configurations.

GRACE Fast Mascons From Spherical Harmonics and a Regularization Design Trade Study

AbstractMass concentration (mascon) solutions have become a prominent medium for investigating time‐variable gravity recovered by GRACE and GRACE Follow‐On. While GRACE Level‐2 spherical harmonic products require various postprocessing techniques to eliminate correlated noise, mascon formulations employ spatial regularization strategies during the estimation step to improve signal recovery. However, mascon estimation has traditionally required large computing resources and GRACE Level‐1B processing capabilities. In this study, we show that a typical mascon estimation system can be reformulated to allow for the estimation of regularized mascons from Level‐2 spherical harmonics. Provided that spherical harmonic solution covariances are available, the computed mascons will be mathematically equivalent to similar mascons estimated from Level‐1B observations. This method is computationally efficient, better leverages GRACE spherical harmonics than past methods, and matches the performance of typical mascon solutions without locking scientists into predetermined regularization designs. We develop a proof‐of‐concept solution using ITSG‐Grace2018 and compare results with traditional mascons from the Jet Propulsion Lab (JPL) and NASA Goddard Space Flight Center (GSFC). We then assess the effects of spherical harmonic truncation and use of regularization correlations on basin signal recovery. We find that spherical expansions to degree and order 60 provide the minimum expansion necessary to study most basins, while larger expansions help further localize signals. We also find that diagonal regularizations (i.e., regularizations that do not contain inter‐mascon correlations) are adversely affected by leakage, especially across boundaries such as coastlines where signals are not highly correlated, whereas including inter‐mascon correlations and regional boundaries in the regularization greatly improves signal recovery.

Multifidelity Space Mission Planning and Infrastructure Design Framework for Space Resource Logistics

To build a sustainable space transportation system for human space exploration, the design and deployment of space infrastructure, such as in situ resource utilization plants, in-orbit propellant depots, and on-orbit servicing platforms, are critical. The design analysis and trade studies for these space-infrastructure systems require the consideration of not only the design of the infrastructure elements themselves, but also their supporting systems (e.g., storage and power) and logistics transportation while exploring various architecture options (e.g., location and technology). This paper proposes a system-level space infrastructure and logistics design optimization framework to perform architecture trade studies. A new space-infrastructure logistics optimization problem formulation is proposed that considers the internal interactions of infrastructure subsystems and their external synergistic effects with space logistics simultaneously. Because the full-size version of this proposed problem formulation can be computationally prohibitive, a new multifidelity optimization formulation is developed by varying the granularity of the commodity-type definition over the space logistics network; this multifidelity formulation can find an approximate solution to the full-size problem computationally efficiently with little sacrifice in the solution quality. The proposed problem formulation and method are applied to the design of in situ resource utilization systems in a multimission lunar exploration campaign to demonstrate their values.

Holistic System Design Evaluation Through Expanded MATE

According to Buede and Miller, not applying a holistic simulation and modeling approach to early design evaluation practices and trade studies results in greater developmental costs, time to market, and unforeseeable system-level design consequences. Completed research is presented for an innovative methodology that enhances the capacity of conventional design evaluations by integrating new types of simulations consistently into the existing Multi-attribute Tradespace Exploration (MATE) design evaluation architecture. This enhancement is particularly important for any envisioned software-intensive system that introduces greater system complexity. According to Ross et al., MATE was originally developed to guide engineering design and initial product selection by exploring candidate designs to deliver utility-based solutions. Unfortunately, the MATE methodology does not support software design evaluation and integration into complex systems. The results presented validate MATE improvements that are scalable and extensible to any software-based system of varying complexity and application. The subject research provides proof of this concept by focusing on sensor systems as an initial practical demonstration due to their rapidly expanding commercial use and Internet of Things (IoT) applications. Project engineers and especially software developers in any product field will benefit from this design method by leveraging its holistic evaluation of software and hardware system design performance for more efficient product design identification and implementation.

Feasibility Study of a Multi-Purpose Aircraft Concept with a Leading-Edge Embedded Cross-Flow Fan

The research presented focuses on investigating the use of Cross-Flow Fan (CFF) as a high-lift device for a Short Take-off and Landing (STOL) aircraft. The wing-embedded fan performance analysis is mostly addressed from an aerodynamic perspective and focuses on using such Active Flow Control (AFC) technology in the conceptual aircraft design process. In particular, the design trade study of an aircraft featuring the fan as a high-lift device applied to a conceptual design of a medium-range multi-purpose aircraft is performed. A sensitivity analysis is employed to investigate the impact of the technology on the aircraft weight, aerodynamics, stability and control, and fight performance. The aircraft design modifications are introduced to maximize the aircraft mission performance given the fan specifications and constraints. Results indicate a reduction of the take-of field length by 18% with the payload penalty of 14%. The aircraft ferry range is also decreased by 7% compared to the baseline aircraft design. The scaling analysis of the aircraft concept is performed to determine the potential market for such technology. The results show that a light General Aviation (GA) airplane or a medium-large size Unmanned Aerial Vehicle (UAV) could benefit more from the wing-embedded CFF compared to more heavy airplanes.

Upper Bound Performance of Shipboard Power and Energy Systems for Early-Stage Design

Shipboard power systems that service large-scale dynamic loads and electric propulsion can significantly improve their performance by adding controllable energy storage. These systems require power management controls that consider dynamics like generator ramp rates, along with energy storage capacity and location. In the early-stage design process, many alternative designs are considered, and each requires a unique controller. This article describes a numerical optimization technique that establishes an upper bound performance criteria without manually designing controllers for each system. The solution is a best case performance that assumes perfect future knowledge of the time-varying load. While unrealistic in real-time, this technique yields a fair comparison between competing architectures without the variability of different control methods. To demonstrate the concept, a notional multi-bus power system architecture is evaluated on a representative set of operational duties to illustrate comparisons between system attributes like energy storage power and efficiency ratings. A design trade study shows that the success rate for a baseline ship can improve from under 60% to nearly 100% by increasing generator power by 10% and energy storage capacity by 100%. These automated architecture benchmarks fit into a broader total ship optimization process, or can be used in human-driven trade studies.

Optimization of eyesafe avalanche photodiode lidar for automobile safety and autonomous navigation systems

Newly emerging accident-reducing, driver-assistance, and autonomous-navigation technology for automobiles is based on real-time three-dimensional mapping and object detection, tracking, and classification using lidar sensors. Yet, the lack of lidar sensors suitable for meeting application requirements appreciably limits practical widespread use of lidar in trucking, public livery, consumer cars, and fleet automobiles. To address this need, a system-engineering perspective to eyesafe lidar-system design for high-level advanced driver-assistance sensor systems and a design trade study including 1.5 - μ m spot-scanned, line-scanned, and flash-lidar systems are presented. A cost-effective lidar instrument design is then proposed based on high-repetition-rate diode-pumped solid-state lasers and high-gain, low-excess-noise InGaAs avalanche photodiode receivers and focal plane arrays. Using probabilistic receiver-operating-characteristic analysis, derived from measured component performance, a compact lidar system is proposed that is capable of 220 m ranging with 5-cm accuracy, which can be readily scaled to a 360-deg field of regard.

Wing weight estimation in conceptual design: a method for strut-braced wings considering static aeroelastic effects

This paper presents a method for the wing weight estimation of strut-braced wing aircraft in conceptual design. The method is simple to implement while still capturing important effects for early design estimates. Static aeroelastic loads, aeroelastic divergence and aileron reversal criteria are calculated directly with small matrices suitable for implementation in spreadsheet software. Maneuver, gust and ground cases are considered. A direct non-iterative method is used for the strut and wing internal loads calculation. The wing and strut load-carrying structures are sized with analytical box-beam equations for strength, buckling and fatigue criteria. Aluminum or composite laminates can be considered. Semi-empirical methods are presented for non-optimal mass components and the secondary structure. The aeroelastic effects and strut reaction estimations are compared for a wide range of design parameters with Nastran validating the proposed method. The weight estimations are verified with conventional aircraft data and strut-braced wing studies available in the literature, showing good accuracy. Design trade studies are presented illustrating typical applications of the method. A potential to reduce the wing mass in about 18 % or to increase the aspect ratio from 10 to 16 compared to a cantilever wing is identified.

Efficient Fluid-Structure Interaction Method for Conceptual Design of Flexible, Fixed-Wing Micro-Air-Vehicle Wings

Micro-air-vehicle wing designs often incorporate flexible structures that mimic the skeletal and membrane attributes found in natural flyers. Accurate performance predictions for these wing types require coupling of aerodynamic and structural simulations. Such fluid–structure interaction simulations are often performed using high-fidelity, numerically expensive techniques such as computational fluid dynamics coupled to nonlinear structural finite element analysis. Although the computational cost of conducting many conceptual design trade studies with these methods is prohibitive, simplified approaches may lack sufficient fidelity to provide conceptual design insights. This paper summarizes the development, comparison, and application of an efficient fluid–structure interaction method to simulate flexible-wing performance for rapid conceptual design of micro air vehicles. An advanced potential flow model computes aerodynamic performance, whereas a corotational frame and shell finite element structural model computes wing deflections due to aerodynamic loading. The paper reviews existing computation approaches, then describes the model formulation, aerodynamic load coupling algorithm, comparisons with a higher fidelity method, and aeroelastic results of wing flexibility parametric and optimization studies at chord-Reynolds numbers of about 75,000. For one specific 304.8 mm wingspan planform, carrying a 0.45 kg payload, the studies indicate the optimized flexible wing achieves 7% endurance parameter gain compared with the stiffer baseline wing.

Vehicle Level Tip-to-Tail Modeling of an Aircraft

A system-level multidisciplinary aircraft model has been developed exclusively in MATLAB/Simulink. Aircraft subsystem models representing the air vehicle system, propulsion system, robust electrical power system, thermal management systems, actuation system and their associated controllers were integrated to investigate the thermal management issues of a long range strike platform. The aircraft model coined tip-to-tail modeling and simulation tool (T2T M&S) allows conceptual design trade studies of various subsystems and can quantify performance gains across the aircraft. As a result, the thermal and power challenges that face modern aircraft can be addressed, potentially increasing the performance capabilities of future aircraft. Preliminary simulation results are discussed with a specific focus on thermal management during mission segments of high thermal demands.

Characterization of Swirl-Venturi Lean Direct Injection Designs for Aviation Gas Turbine Combustion

Injector geometry, physical mixing, chemical processes, and engine cycle conditions together govern performance, operability, and emission characteristics of aviation gas turbine combustion systems. The present investigation explores swirl-venturi lean direct injection combustor fundamentals, characterizing the influence of key geometric injector parameters on reacting flow physics and emission production trends. In this computational study, a design space exploration was performed using a parameterized swirl-venturi lean direct injector model. From the parametric geometry, 20 three-element lean direct injection combustor sectors were produced and simulated using steady-state Reynolds-averaged Navier–Stokes reacting computations. Species concentrations were solved directly using a reduced 18-step reaction mechanism for Jet A. Turbulence closure was obtained using a nonlinear model. Results demonstrate sensitivities of the geometric perturbations on axially averaged flowfield responses. Output variables include axial velocity, turbulent kinetic energy, static temperature, fuel patternation, and minor species mass fractions. Significant trends have been reduced to surrogate model approximations, intended to guide future injector design trade studies and advance aviation gas turbine combustion research.

Modeling Techniques for a Computational Efficient Dynamic Turbofan Engine Model

A transient two-stream engine model has been developed. Individual component models developed exclusively in MATLAB/Simulink including the fan, high pressure compressor, combustor, high pressure turbine, low pressure turbine, plenum volumes, and exit nozzle have been combined to investigate the behavior of a turbofan two-stream engine. Special attention has been paid to the development of transient capabilities throughout the model, increasing physics model, eliminating algebraic constraints, and reducing simulation time through enabling the use of advanced numerical solvers. The lessening of computation time is paramount for conducting future aircraft system-level design trade studies and optimization. The new engine model is simulated for a fuel perturbation and a specified mission while tracking critical parameters. These results, as well as the simulation times, are presented. The new approach significantly reduces the simulation time.

Using Probabilistic Computational Durability Modeling and Simulation to Create a Virtual Design of Experiments Based on Limited Laboratory Tests

Laboratory testing is essential in understanding the fatigue durability limits of a medical device. Only a limited number of tests, however, are feasible considering the time and cost of manufacturing and testing the device. Many geometries and materials are available as design alternatives and testing is typically constrained to a limited number of devices. Additionally, physical test method capability typically has limitations and uncertainty for such breath of design alternatives. The time and cost is greatly magnified if the designs do not meet the durability test requirements. This leads to an important question, “How do we combine results from the laboratory testing of similar designs and similar materials with state-of-the-art computational methods to create the best possible understanding of the design space?” The Virtual Life Management® (VLM) methodology accomplishes this by creating a Virtual Design of Experiment: a computational method that combines structural analysis (FEA) data, material characterization models and probabilistic methods.For a specific Context of Use, using a computational approach, a) the structural analysis (FEA) models are used to understand the effect of the boundary conditions and loads on the stresses, stress gradients and stressed volumes, b) the material models are used to understand the damage induced by the stresses, and c) probabilistic and Monte Carlo methods are used to extend the design of experiment to high reliability levels and understand the design space at the statistical tails of the durability distribution i.e., Minimum Device Lifetime. The sensitivity of the minimum lifetime to the design parameter will be different than the sensitive at nominal lifetimes. Only by predicting the tails of the distribution can we quantify the durability of the design in the marketplace. This process is pictorially depicted in Fig. 1.Boston Scientific has been working with VEXTEC to create probabilistic microstructural material models for computational strength prediction and then combining these with structural analysis (FEA) and Virtual Life Management to predict risk i.e., probability of failure of a device. Two specific devices and Contexts of Use include: a) pacemaker leads made of MP35N material subject to two amplitudes of bending fatigue and b) endoscopic airway stent made of Nitinol material subject to a crushing load to represent stent deformation depicting a cough. For the airway stent effort, VLM was able to estimate the fatigue lifetime of stent design before stent is manufactured and tested. The simulation was able to show difference in average fatigue lifetime for two Nitinol alloy lots with different inclusion contents (and both complied with the specification (ASTM2063-05)). This was confirmed by the few (∼10) experiments completed. Significantly, VLM was able to predict a large difference for the −3σ fatigue lifetime for the two flavors of Nitinol. (Experimentally this would have required a large number of tests.) For the pacemaker leads project, VLM was able to characterize the lead design as a function of material microstructure (grain size, inclusion size and density) while using residual stress as a calibrating parameter (shown in Fig. 2). This study was able to demonstrate VLM's ability to iterate with material substitution, vendor management, sensitivity analysis, design trade studies and design optimization. To summarize, merging material science with computational methods opens a whole new level of engineering capabilities specifically uncertainty quantification and probabilistic distributions associated with microstructural characterization; a key step in supporting the verification and validation framework being developed by the ASME V&amp;V 40 standard for medical devices.Although the work to date is early stage, the favorable results have provided confidence in the methodology and toolset; and insight to the potential application in the formal medical device product development process.

Adaptive Control of Quadrotor UAVs: A Design Trade Study With Flight Evaluations

This brief describes the application of direct and indirect model reference adaptive control to a lightweight low-cost quadrotor unmanned aerial vehicle platform. A baseline trajectory tracking controller is augmented by an adaptive controller. The approach is validated using simulations and flight tested in an indoor test facility. The adaptive controller is found to offer increased robustness to parametric uncertainties. In particular, it is found to be effective in mitigating the effects of a loss-of-thrust anomaly, which may occur due to component failure or physical damage. The design of the adaptive controller is presented, followed by a comparison of flight test results using the existing linear and augmented adaptive controllers.

A case for trading risk in complex conceptual design trade studies

Complex conceptual system design trade studies traditionally consider risk after a conceptual design has been created. Further, one person is often tasked with collecting risk information and managing it from each subsystem. This paper proposes a method to explicitly consider and trade risk on the same level as other important system-level variables during the creation of conceptual designs in trade studies. The proposed risk trading method advocates putting each subsystem engineer in control of risk for each subsystem. A risk vector is proposed that organizes many different risk metrics for communication between subsystems. A method of coupling risk models to dynamic subsystem models is presented. Several risk visualization techniques are discussed. A trade study example is presented based upon a simplified spacecraft model. Results from introducing the risk trading methodology into a simulated Collaborative Design Center are presented. The risk trading method offers an approach to more thoroughly consider risk during the creation of conceptual designs in trade studies.

Form Factor and Critical Mach Number Estimation for Finite Wings

Empirical methods used in conceptual aircraft design for the calculation of form factor drag and critical Mach number typically have been based on two-dimensional profile considerations alone or, at most, limited wing parameters. This paper compares many of these legacy methods. Motivated by the limited wing features modeled in current approaches, surrogate models for form factor and critical Mach number have been built as functions of airfoil thickness and trapezoidal wing parameters. These surrogate models are regressed from the results of a threedimensional potential flow solution coupled to a profile boundary-layer analysis. The surrogates are physics based, yet their simple functional forms make them applicable for inclusion in aircraft sizing algorithms for rapid conceptual and preliminary design trade studies. The models capture the increasing influence of tip effects and spanwise flow as the aspect ratio is decreased and sweep is increased. A primary finding is the strongly beneficial effects of reduced aspect ratio on the form drag and critical Mach number of thick wings.

Robust and Adaptive Control of X-45A J-UCAS: A Design Trade Study

AbstractThis paper presents a control design trade study related to robust and adaptive control methods for an autonomous aerial platform representative of the Boeing / USAF X-45A Joint Unmanned Combat Air System (J-UCAS). Control architectures and methodologies selected for this study include a robust baseline augmented by a direct adaptive model reference controller with various recently developed modifications. Specifically, inner-loop flight control design using robust adaptive methods is performed, and closed-loop system tracking performance is demonstrated in simulation environment.