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  • 1
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    Quieting a Rib-Framed Honeycomb Core Sandwich Panel for a Rotorcraft Roof (2017)
    In:  CASI
    Details
    Publication Date: 2019-06-12
    Description: A rotorcraft roof composite sandwich panel has been redesigned to optimize sound power transmission loss (TL) and minimize structure-borne sound for frequencies between 1 and 4 kHz where gear-meshing noise from the transmission has the most impact on speech intelligibility. The roof section, framed by a grid of ribs, was originally constructed of a single honeycomb core/composite face sheet sandwich panel. The original panel has acoustic coincidence frequencies near 600 Hz, leading to poor TL across the frequency range of 14 kHz. To quiet the panel, the cross section was split into two thinner sandwich subpanels separated by an air gap. The air gap was sized to target the fundamental mass-spring-mass resonance of the panel system to less than 500 Hz, well below the frequency range of interest. The panels were designed to withstand structural loading from normal rotorcraft operation, as well as "man-on-the-roof" static loads experienced during maintenance operations. Thin layers of viscoelastomer were included in the face sheet ply layups, increasing panel damping loss factors from about 0.01 to 0.05. TL measurements show the optimized panel provides 611 dB of acoustic TL improvement and 615 dB of structure-borne sound reduction at critical rotorcraft transmission tonal frequencies. Analytic panel TL theory simulates the measured performance within 3 dB over most frequencies. Detailed finite element/boundary element modeling simulates TL slightly more accurately, within 2 dB for frequencies up to 4 kHz, and also simulates structure-borne sound well, generally within 3 dB.
    Keywords: Aircraft Design, Testing and Performance
    Type: NF1676L-26307 , Journal of the American Helicopter Society (ISSN 2161-6027); 62; 1; 1-10
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  • 2
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    Attitude Control System for a Balloon Based Telescope (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is an 8-meter interferometer which operates on a high-altitude balloon. BETTII had its first successful engineering flight in June 2017. In this paper we discuss the design of the control system for BETTII, which includes the coarse pointing loop and the estimator controls algorithm (Extended Kalman Filter) implemented in FPGA. We will also discuss the different system modes that we defined in the controls system loop, which are used in different phases of the flight and are activated in order to acquire a target star in the science detector. The pointing loop uses different sensors and actuators in each phase to keep pointing at the desired target. The main sensors aregyroscopes, star cameras, and auxiliary sensors such as high-altitude GPS and magnetometers. The azimuth control is achieved with Compensated Controlled Moment Gyros (CCMG) and a Momentum Dump motor. For the elevation control, high-precision motors are used, which change the elevation of the siderostat mirrors. The combination of these instruments keep the baseline oriented within few arcseconds from the target star.In this paper, we will also present the software architecture relevant to the control system. This includes the description of the two flight computers present on the payload and the different control loops that are executed on them. Similarly, we will explain the importance of synchronization between all the sensors and actuators, which have to be referenced to a single master clock in order to obtain science data.
    Keywords: Optics
    Type: GSFC-E-DAA-TN67041 , SPIE Defense + Security 2018; Apr 15, 2018 - Apr 19, 2018; Orlando, FL; United States
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  • 3
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    Fabrication and Characterization of a NIR-FIR Dichroic for the Infrared Interferometer BETTII (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: BETTII is a balloon-borne far infra-red (FIR: 30-100 m) interferometer that also uses a near-infrared (NIR: 1-2.5 m) channel for fine pointing sensing using stars. We have developed an inductive grid dichroic to divide the incoming beam into two components, by reflecting FIR light and transmitting NIR light. The dichroic is fabricated using focused electron beam technology to produce a 1 m period, 100 nm width metal grid on a sapphire substrate in order to have high reflectance for FIR wavelengths. Here we discuss the design and the detailed manufacturing process for such a dichroic. The transmission and reflectance characteristics are also presented. We discuss them in context of the BETTII requirements.
    Keywords: Astronomy; Instrumentation and Photography
    Type: GSFC-E-DAA-TN67073 , GSFC-E-DAA-TN67055 , Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX; 10708; 107083I|SPIE Astronomical Telescopes + Instrumentation; Jun 12, 2018 - Jun 14, 2018; Austin, TX; United States
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  • 4
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    Toward Reduced Aircraft Community Noise Impact Via a Perception-Influenced Design Approach (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This is an exciting time for aircraft design. New configurations, including small multi-rotor uncrewed aerial systems, fixed- and tilt-wing distributed electric propulsion aircraft, high-speed rotorcraft, hybrid-electric commercial transports, and low-boom supersonic transports, are being made possible through a host of propulsion and airframe technology developments. The resulting noise signatures may be radically different, both spectrally and temporally, than those of the current fleet. Noise certification metrics currently used in aircraft design do not necessarily reflect these characteristics and therefore may not correlate well with human response. Further, as operations and missions become less airport-centric, e.g., those associated with on-demand mobility or package delivery, vehicles may operate in closer proximity to the population than ever before. Fortunately, a new set of tools are available for assessing human perception during the design process in order to affect the final design in a positive manner. The tool chain utilizes system noise prediction methods coupled with auralization and psychoacoustic testing, making possible the inclusion of human response to noise, along with performance criteria and certification requirements, into the aircraft design process. Several case studies are considered to illustrate how this approach could be used to influence the design of future aircraft.
    Keywords: Acoustics; Aircraft Design, Testing and Performance
    Type: NF1676L-23666 , Inter-Noise 2016 Conference; Aug 21, 2016 - Aug 24, 2016; Hamburg; Germany
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  • 5
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    Simulation of Rotorcraft Fly-In Noise (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-21243 , Acoustics Technical Working Group Meeting (ATWG 2015); Apr 21, 2015 - Apr 22, 2015; Hampton, VA; United States
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  • 6
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    Recent Aeroacoustic Tools and Methods Developments for Analysis and Design of Advanced Aviation Systems (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Acoustics; Aircraft Design, Testing and Performance
    Type: NF1676L-20548 , AIAA Aerospace Sciences Meeting (AIAA SciTech 2015); Jan 05, 2015 - Jan 09, 2015; Kissimmee, FL; United States
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  • 7
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    Schedule Matters: Understanding the Relationship between Schedule Delays and Costs on Overruns (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper examines the relationship between schedule delays and cost overruns on complex projects. It is generally accepted by many project practitioners that cost overruns are directly related to schedule delays. But what does "directly related to" actually mean? Some reasons or root causes for schedule delays and associated cost overruns are obvious, if only in hindsight. For example, unrealistic estimates, supply chain difficulties, insufficient schedule margin, technical problems, scope changes, or the occurrence of risk events can negatively impact schedule performance. Other factors driving schedule delays and cost overruns may be less obvious and more difficult to quantify. Examples of these less obvious factors include project complexity, flawed estimating assumptions, over-optimism, political factors, "black swan" events, or even poor leadership and communication. Indeed, is it even possible the schedule itself could be a source of delay and subsequent cost overrun? Through literature review, surveys of project practitioners, and the authors' own experience on NASA programs and projects, the authors will categorize and examine the various factors affecting the relationship between project schedule delays and cost growth. The authors will also propose some ideas for organizations to consider to help create an awareness of the factors which could cause or influence schedule delays and associated cost growth on complex projects.
    Keywords: Economics and Cost Analysis
    Type: GSFC-E-DAA-TN29214 , 2016 IEEE Aerospace Conference; Mar 05, 2016 - Mar 12, 2016; Big Sky, MT; United States
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  • 8
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    Historical Mass, Power, Schedule, and Cost Growth for NASA Spacecraft (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Although spacecraft developers have been moving towards standardized product lines as the aerospace industry has matured, NASA's continual need to push the cutting edge of science to accomplish unique, challenging missions can still lead to spacecraft resource growth over time. This paper assesses historical mass, power, cost, and schedule growth for multiple NASA spacecraft from the last twenty years and compares to industry reserve guidelines to understand where the guidelines may fall short. Growth is assessed from project start to launch, from the time of the preliminary design review (PDR) to launch and from the time of the critical design review (CDR) to launch. Data is also assessed not just at the spacecraft bus level, but also at the subsystem level wherever possible, to help obtain further insight into possible drivers of growth. Potential recommendations to minimize spacecraft mass, power, cost, and schedule growth for future missions are also discussed.
    Keywords: Spacecraft Design, Testing and Performance
    Type: GSFC-E-DAA-TN28907 , 2016 IEEE Aerospace Conference; Mar 05, 2016 - Mar 12, 2016; Big Sky, MT; United States
    Format: text
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  • 9
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    The Business Change Initiative: A Novel Approach to Improved Cost and Schedule Management (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Goddard Space Flight Center's Flight Projects Directorate employed a Business Change Initiative (BCI) to infuse a series of activities coordinated to drive improved cost and schedule performance across Goddard's missions. This sustaining change framework provides a platform to manage and implement cost and schedule control techniques throughout the project portfolio. The BCI concluded in December 2014, deploying over 100 cost and schedule management changes including best practices, tools, methods, training, and knowledge sharing. The new business approach has driven the portfolio to improved programmatic performance. The last eight launched GSFC missions have optimized cost, schedule, and technical performance on a sustained basis to deliver on time and within budget, returning funds in many cases. While not every future mission will boast such strong performance, improved cost and schedule tools, management practices, and ongoing comprehensive evaluations of program planning and control methods to refine and implement best practices will continue to provide a framework for sustained performance. This paper will describe the tools, techniques, and processes developed during the BCI and the utilization of collaborative content management tools to disseminate project planning and control techniques to ensure continuous collaboration and optimization of cost and schedule management in the future.
    Keywords: Astronautics (General); Economics and Cost Analysis
    Type: GSFC-E-DAA-TN29217 , 2016 IEEE Aerospace Conference; Mar 05, 2016 - Mar 12, 2016; Big Sky, MT; United States
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  • 10
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    Contribution of Schedule Delays to Cost Growth: How to Make Peace with a Marching Army (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Numerous research papers have shown that cost and schedule growth are interrelated for NASA space science missions. Although there has shown to be a strong correlation of cost growth with schedule growth, it is unclear what percentage of cost growth is caused by schedule growth and how schedule growth can be controlled. This paper attempts to quantify this percentage by looking at historical data and show detailed examples of how schedule growth influences cost growth. The paper also addresses a methodology to show an alternate approach for assessing and setting a robust baseline schedule and use schedule performance metrics to help assess if the project is performing to plan. Finally, recommendations are presented to help control schedule growth in order to minimize cost growth for NASA space science missions.
    Keywords: Astronautics (General)
    Type: GSFC-E-DAA-TN28889 , 2016 IEEE Aerospace Conference; Mar 05, 2016 - Mar 12, 2016; Big Sky, MT; United States
    Format: text
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