University Affiliated Research Center

University, MS, United States

University Affiliated Research Center

University, MS, United States
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Chen N.Y.,NASA | Chen N.Y.,Research Aerospace Engineer | Sridhar B.,NASA | Ng H.K.,University of California at Santa Cruz | Ng H.K.,University Affiliated Research Center
Journal of Aircraft | Year: 2012

This paper describes a class of strategies for reducing persistent contrail formation with the capability of trading off between contrails and aircraft-induced emissions. The concept of contrail-frequency index is defined and used to quantify the contrail activities. The contrail-reduction strategies reduce the contrail-frequency index by altering aircraft's cruising altitude with consideration to extra emissions. The strategies use a user-defined factor to trade off between contrail reduction and extra emissions. The analysis shows that contrails can be reduced with extra emissions and without adding congestion to airspace. For a day with high contrail activities, the results show that the maximal contrail-reduction strategy can achieve a contrail reduction of 88%. When a tradeoff factor is used, the strategy can achieve less contrail reduction while emitting less emissions compared to the maximal contrail-reduction strategy. The user-defined tradeoff factor provides a flexible way to trade off between contrail reduction and extra emissions. Better understanding of the tradeoffs between contrails and emissions and their impact on the climate need to be developed to fully use this class of contrail-reduction strategies. The strategies provide a starting point for developing operational policies to reduce the impact of aviation on climate. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.


Xue M.,University of California at Santa Cruz | Xue M.,University Affiliated Research Center | Zelinski S.,NASA
15th AIAA Aviation Technology, Integration, and Operations Conference | Year: 2015

In terminal airspace, integrating arrivals, departures, and surface operations with competing resources provides the potential of improving operational efficiency by removing barriers between different operations. This work develops a centralized stochastic scheduler for operations in a terminal area including airborne and surface operations using a non-dominated sorting genetic algorithm and Monte Carlo simulations. The scheduler handles competing resources between different flows, such as runway allocations, runway crossings, merges at departure fixes, and other interaction waypoints between arrivals and departures. The scheduler takes time-varied uncertainties into account in optimization as well. The scheduler is run sequentially to identify the best robust schedule for the next planning window. Resulting schedules determine routes, speeds or delays, and runway assignments subject to separation constraints at merging diverging waypoints in the air and at runways (including runway crossings) on the surface. The Los Angeles terminal area was used as an example in experiments with a four-hour traffic scenario. The results showed that using stochastic schedulers can reduce flight time delay (airborne and ground) anywhere from 28% to 40% statistically compared to deterministic schedulers. Sensitivity studies on various planning horizons presented that trade-offs exist between planning horizons and achievable minimum delays. A twenty-minute planning horizon was found to be a bad choice because uncertainties increased with the look-ahead time. Eight minutes was promising for planning as it achieved the lowest delay compared to others. However, the results demonstrated that any duration from two minutes to eight minutes could be a good candidate as well. The results on runway usage showed that using the stochastic scheduler, runway makespans and occupancy were usually slightly lower than applying deterministic schedulers. © 2015, American Institute of Aeronautics and Astronautics Inc.


Giannakopoulou D.,Carnegie Mellon University | Bushnell D.H.,NASA | Schumann J.,NASA | Erzberger H.,University of California at Santa Cruz | Heere K.,University Affiliated Research Center
Annals of Mathematics and Artificial Intelligence | Year: 2011

In order to address the rapidly increasing load of air traffic operations, innovative algorithms and software systems must be developed for the next generation air traffic control. Extensive verification of such novel algorithms is key for their adoption by industry. Separation assurance algorithms aim at predicting if two aircraft will get closer to each other than a minimum safe distance; if loss of separation is predicted, they also propose a change of course for the aircraft to resolve this potential conflict. In this paper, we report on our work towards developing an advanced testing framework for separation assurance. Our framework supports automated test case generation and testing, and defines test oracles that capture algorithm requirements. We discuss three different approaches to test-case generation, their application to a separation assurance prototype, and their respective strengths and weaknesses. We also present an approach for statistical analysis of the large numbers of test results obtained from our framework. © 2011 Springer Science+Business Media B.V.


Evans A.D.,University of California at Santa Cruz | Evans A.D.,University Affiliated Research Center | Lee P.,NASA
16th AIAA Aviation Technology, Integration, and Operations Conference | Year: 2016

When weather or congestion impacts the National Airspace System, multiple different Traffic Management Initiatives can be implemented, sometimes with unintended consequences. One particular perceived inequity that is commonly identified is in the interaction between Ground Delay Programs (GDPs) and time based scheduling of internal departures by the Traffic Management Advisor (TMA) (now operationally superseded by the FAA’s the Time-Based Flow Management system). Internal departures under TMA scheduling can take large GDP delays, followed by large TMA scheduling delays, because they cannot easily fit into the arrival flow at the runway. In this paper we examine the causes of these ‘double delays’ through an analysis of arrival operations at Newark Liberty International Airport (EWR) from June to August 2010. TMA scheduling delays are found to be generally higher than TMA airborne metering delays, regardless of prior GDP delays. Depending on how the double delay is defined, between 42% and 62% of all internal departures in GDP and TMA scheduling experienced double delays in this period. A deep dive into the data reveals that contributors to double delays include upstream flights departing before their Expect Departure Clearance Times (EDCTs); differences in the rates used for setting EDCTs and TMA Scheduled Times of Arrival; differences in the arrival demand expected based on EDCTs and the arrival demand entering TMA; and shorter en route times between takeoff and entry into TMA than assumed in the calculation of flight EDCTs, all of which undermine the sequencing and spacing underlying flight EDCTs. Double delays are also found to coincide with periods in which the virtual runway arrival queue being served by a TMA is large, there are periods of high demand relative to capacity, and there are high airborne metering delays. Data mining techniques are used to confirm that each of these factors contribute to the occurrence of double delay and/or high internal departure scheduling delay across three months of data from June to August 2010. Predictors of the occurrence of double delay and high TMA scheduling delay are built using logistic regression, providing prediction accuracies of 69% and 73%, respectively. © 2016 American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.


Xue M.,University of California at Santa Cruz | Xue M.,University Affiliated Research Center
AIAA Guidance, Navigation, and Control Conference | Year: 2010

In the national airspace system, sectors get overloaded due to high traffic demand and inefficient airspace designs. Overloads can be eliminated in some cases by redesigning sector boundaries. This paper extends the Voronoi-based sector design method by automatically selecting the number of sectors, allowing three-dimensional partitions, and enforcing traffic pattern conformance. The method was used to design sectors at Fort-Worth and Indianapolis centers for current traffic scenarios. Results show that new designs can eliminate overloaded sectors, although not in all cases, reduce the number of necessary sectors, and conform to major traffic patterns. Overall, the new methodology produces enhanced and efficient sector designs. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.


Xue M.,University of California at Santa Cruz | Xue M.,University Affiliated Research Center
Journal of Guidance, Control, and Dynamics | Year: 2012

In the national airspace system, sectors get overloaded due to high traffic demand and inefficient airspace designs. Overloads can be eliminated in some cases by redesigning sector boundaries. This paper extends the Voronoi-based sector design method by automatically selecting the number of sectors, allowing three-dimensional partitions, and enforcing traffic pattern conformance. The method was used to design sectors at the Fort Worth and Indianapolis Air Route Traffic Control Centers for current traffic scenarios. Results show that new designs can eliminate overloaded sectors (although not in all cases), reduce the number of necessary sectors, and conform to major traffic patterns. Overall, the new methodology produces enhanced and efficient sector designs.


Gong C.,NASA | McNally D.,NASA | Lee C.H.,University Affiliated Research Center
15th AIAA Aviation Technology, Integration, and Operations Conference | Year: 2015

Convective weather can cause arrival traffic to fly less efficient weather avoidance routes and is the primary cause for time-based metering to be discontinued. Dynamic Arrival Routes (DAR) is a trajectory-based weather avoidance system that is designed to help improve arrival traffic flow when weather is present. The DAR system continuously analyzes airborne arrival flights for opportunities to reroute them to more efficient arrival routes or around weather that is predicted to be on their current flight plan early enough to allow the arrival time-based metering system to adjust its times of arrival for the presence of weather. Analysis of 93 hours of actual traffic over 12 different days from Fort Worth Center showed DAR proposed more efficient arrival reroutes for 352 arrival flights for an average time savings of 12.3 minutes per flight at a look-ahead time of 60 minutes from the meter fix. DAR also identified 642 arrival flights with a need to deviate around weather and proposed weather avoidance routes that were analytically shown to remain weather-free 83 percent of the time for a look-ahead time of 30 minutes from the meter fix. © 2015 American Institute of Aeronautics and Astronautics Inc, AIAA. All right reserved.


Winter M.W.,NASA | Winter M.W.,University Affiliated Research Center | Trumble K.A.,NASA
Journal of Spacecraft and Rockets | Year: 2011

Thermal radiation of the heatshield and the emission of the postshock layer around the Stardust capsule, during its reentry, were detected by a NASA-led observation campaign aboard NASA's DC-8 airborne observatory involving teams from several nations. The German SLIT experiment used a conventional spectrometer, in a Czerny-Turner configuration (300 mm focal length and a 600 lines/mm grating), fed by fiber optics, to cover a wavelength range from 324 to 456 nm with a pixel resolution of 0.08 nm. The reentering spacecraft was tracked manually using a camera with a view angle of 20 deg, and light from the capsule was collected using a small mirror telescope with a view angle of only 0.45 deg. Data were gathered with a measurement frequency of 5 Hz in a 30-s time interval around the point of maximum heating until the capsule left the field of view. The emission of carbon nitride (as a major ablation product), N + 2 and different atoms were monitored successfully during that time. Because of the nature of the experimental setup, spatial resolution of the radiation field was not possible. Therefore, all measured values represent an integration of radiation from the visible part of the glowing heatshield, and from the plasma in the postshock region. Further, due to challenges in tracking, not every spectrum gathered contained data. The measured spectra can be split up into two parts: 1) continuum spectra, which represent a superposition of the heatshield radiation and the continuum radiation of particles due to microspallation in the plasma, and 2) line spectra from the plasma in the shock layer. Planck temperatures (interpreted as the surface temperatures of the Stardust heatshield) were determined assuming either a constant surface temperature, or a temperature distribution deduced from numerical simulation. The constant surface temperatures are in good agreement with numerical simulations, but the peak values at the stagnation point are significantly lower than those in the numerical simulation if a temperature distribution over the surface is assumed. Emission bands of carbon nitride and N + 2 were tracked along the visible trajectory and compared with a spectral simulation with satisfying agreement. Values for the integrated radiation of the transitions of interest for these species were extracted from this comparison. Copyright © 2010 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc.


Lee S.M.,University Affiliated Research Center | Mueller E.R.,NASA
2013 Aviation Technology, Integration, and Operations Conference | Year: 2013

In integrating Unmanned Aircraft Systems (UAS) into the National Airspace System, separation assurance is one of the important air traffic services for ensuring safe operations of air traffic. This paper describes an approach to develop a range of operational concepts by describing what functions and technologies are required to maintain safe separation of unmanned aircraft and how those functions are allocated and distributed across primary system elements, such as air traffic controllers, automation systems, aircraft onboard systems, and UAS ground control stations including UAS pilots. A framework proposed in this study identifies key functions and capabilities by decomposing high-level system goals into smaller functions to achieve them hierarchically and also identifies primary system elements to perform the identified functions by decomposing the whole system into smaller systems hierarchically. The framework represents hierarchical functional/physical structure and allocation of functions across system elements at different levels to generate a range of potential separation assurance concepts systematically. The detailed representation of functional decomposition and allocation enables an application of the framework for recommending levels of automation (LOA) developed based on human factors engineering principles. The detailed functional decomposition and allocation framework to develop a concept of operations provides additional analysis capabilities: stability, workflow, and task-load analysis to examine the completeness, correctness, and balance of functional decomposition and allocation schemes for concept development without requiring complex simulations. This paper demonstrates the framework through a case study of providing separation assurance functions for UAS operating in en-route and transition airspace in the Next Generation Air Transportation System (NextGen) timeframe.


Mukherjee A.,University Affiliated Research Center | Grabbe S.,NASA | Sridhar B.,NASA
AIAA Guidance, Navigation, and Control Conference 2011 | Year: 2011

Delays caused by uncertainty in weather forecasts can be reduced by improving traffic flow management decisions. This paper presents a methodology for traffic flow management under uncertainty in convective weather forecasts. An algorithm for assigning departure delays and reroutes to aircraft is presented. Departure delay and route assignment are executed at multiple stages, during which, updated weather forecasts and flight schedules are used. At each stage, weather forecasts up to a certain look-ahead time are treated as deterministic and flight scheduling is done to mitigate the impact of weather on fourdimensional flight trajectories. Uncertainty in weather forecasts during departure scheduling results in tactical airborne holding of flights. The amount of airborne holding depends on the accuracy of forecasts as well as the look-ahead time included in the departure scheduling. The weather forecast look-ahead time is varied systematically within the experiments perfomed in this paper to analyze its effect on flight delays. Based on the results, longer look-ahead times cause higher departure delays and additional flying time due to reroutes. However, the amount of airborne holding necessary to prevent weather incursions reduces when the forecast look-ahead times are higher. For the chosen day of traffic and weather, setting the look-ahead time to 90 minutes yields the lowest total delay cost.

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