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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Modulation Study for Beam Steerable Reflectarray Antennas

The reflectarray antenna is a power-efficient antenna but with an inherent intersymbol interference (ISI) problem with digital modulations. The composite signal model of a reflectarray is established. The ISI is characterized by the signal components delays. The feed-to-element distance and the element-to-observation distance contribute to the total delay, with the latter having the major effect. The effect of typical phase shifters' phase errors is analyzed and evaluated. Simulations are performed. The analytical and simulation results for an example reflectarray at f(sub c) = 26.5 GHz and bit rate of 1.325 Gbps show that the BER degradation due to ISI is proportional to the symbol rate and the loss ranges from less than 1 dB to around 2 dB in E(sub b)/N(sub o), depending on original E(sub b)/N(sub o), for BPSK, QPSK, 8PSK and 16QAM. The phase error effect is negligible for lower order modulations and is unacceptable for higher order modulations such as 64 and 256QAM.

Xiong, Fuqin↗
NASA NTRSDate not supplied

Development and Demonstration of a Digital NDE Pipeline for Streamlined Analysis of Ultrasonic Data

Currently when nondestructive evaluation (NDE) is performed on composite structures, the results, although recorded digitally are often manually interpreted and indicated (drawn) on the part being inspected by hand. Following this, a determination must be made on how to disposition that part. This decision could be based on engineering guidelines and best practices, rule-of-thumb, expert opinion or finite-element analysis of the part with some approximate representation of the damage. In order to streamline this process for ultrasonic inspection an effort was undertaken as part of NASA Advanced Composites Project to develop the Digital NDE Pipeline. The Digital NDE Pipeline is an integrated tool suite and associated framework that streamlines the inspection and defect disposition process through model-assisted inspection optimization, automated defect analysis of NDE data, and mapping of NDE data into finite element analysis software. This paper will provide an overview of the Digital NDE Pipeline and provide details of the individual tools developed along with the results of applying these tools to a demonstration test case.

Composites↗
NASA NTRS1987

Measuring the Interlaminar Shear Strengths of Composites

Acousto-ultrasonic technique utilizing computer and waveform digitizer developed for nondestructive evaluation (NDE) of composite materials. Technique employed on filament-wound composite (FWC) specimens cut from sample segments of graphite/epoxy cylinders. Developed for use on large composite structures to verify integrity and assure reusability. Similar applications of technique anticipated for variety of composite structures, such as pipelines and storage tanks.

Kautz, Harold E.↗
NASA NTRS1998

Composite x-ray image assembly for large-field digital mammography with one- and two-dimensional positioning of a focal plane array

To demonstrate the feasibility of a novel large-field digital mammography technique, a 1024 x 1024 pixel Loral charge-coupled device (CCD) focal plane array (FPA) was positioned in a mammographic field with one- and two-dimensional scan sequences to obtain 950 x 1800 pixel and 3600 x 3600 pixel composite images, respectively. These experiments verify that precise positioning of FPAs produced seamless composites and that the CCD mosaic concept has potential for high-resolution, large-field imaging. The proposed CCD mosaic concept resembles a checkerboard pattern with spacing left between the CCDs for the driver and readout electronics. To obtain a complete x-ray image, the mosaic must be repositioned four times, with an x-ray exposure at each position. To reduce the patient dose, a lead shield with appropriately patterned holes is placed between the x-ray source and the patient. The high-precision motorized translation stages and the fiber-coupled-scintillating-screen-CCD sensor assembly were placed in the position usually occupied by the film cassette. Because of the high mechanical precision, seamless composites were constructed from the subimages. This paper discusses the positioning, image alignment procedure, and composite image results. The paper only addresses the formation of a seamless composite image from subimages and will not consider the effects of the lead shield, multiple CCDs, or the speed of motion.

Mammography/methods/statistics & numerical data↗
NASA NTRS1979

Quiet Clean Short-haul Experimental Engine (QCSEE)

The design, fabrication, and testing of two experimental propulsion systems for powered lift transport aircraft are given. The under the wing (UTW) engine was intended for installation in an externally blown flap configuration and the over the wing (OTW) engine for use in an upper surface blowing aircraft. The UTW engine included variable pitch composite fan blades, main reduction gear, composite fan frame and nacelle, and a digital control system. The OTW engine included a fixed pitch fan, composite fan frame, boilerplate nacelle, and a full authority digital control. Many acoustic, pollution, performance, and weight goals were demonstrated.

Willis, W. S.↗
NASA NTRS1980

Graphics and composite material computer program enhancements for SPAR

User documentation is provided for additional computer programs developed for use in conjunction with SPAR. These programs plot digital data, simplify input for composite material section properties, and compute lamina stresses and strains. Sample problems are presented including execution procedures, program input, and graphical output.

Farley, G. L.↗
NASA NTRS1970

Digital phase-modulation/multiplex system

System combines and modulates subcarriers and pulse code modulation data entirely with digital logic, and phase modulates an RF carrier with a digital representation of the composite subcarrier signal. It permits programmed control and modification of the modulation indices.

Couvillon, L. A.↗
NASA NTRS1975

Quiet clean short-haul experimental engine /QCSEE/ design rationale

The principal design features of the NASA QCSEE Under-The-Wing and Over-The-Wing powered lift propulsion systems are given. In the UTW engine, these include noise reduction features, a variable pitch low pressure ratio fan, a fan drive reduction gear, an advanced core and low pressure turbine with a low pollution combustor, a digital control, and advanced composite construction for the inlet, fan frame, fan exhaust duct, and variable area fan exhaust nozzle. The OTW engine is similar but has higher fan pressure and a fixed pitch fan. Both engines are scheduled to be fabricated and tested starting in 1976.

Adamson, A. P.↗
NASA NTRS1980

Qualification of HiMAT flight systems

The highly maneuverable aircraft technology (HiMAT) remotely piloted research vehicle is discussed with emphasis on the advanced composite and metallic structures, digital fly-by-wire controls, and digitally implemented integrated propulsion control systems. Techniques used to qualify the systems for flight are examined. Computation and simulation of the HiMAT system are investigated in relation to Cyber-Varian simulation. The techniques used in flight qualification are complicated by ground based flight critical systems and severe onboard volume constraints imposed by the scale design.

Myers, A. F.↗
NASA NTRS1983

Conceptual design of a data reduction system

A telemetry data processing system was defined of the Data Reduction. Data reduction activities in support of the developmental flights of the Space Shuttle were used as references against which requirements are assessed in general terms. A conceptual system design believed to offer significant throughput for the anticipated types of data reduction activities is presented. The design identifies the use of a large, intermediate data store as a key element in a complex of high speed, single purpose processors, each of which performs predesignated, repetitive operations on either raw or partially processed data. The recommended approach to implement the design concept is to adopt an established interface standard and rely heavily on mature or promising technologies which are considered main stream of the integrated circuit industry. The design system concept, is believed to be implementable without reliance on exotic devices and/or operational procedures. Numerical methods were employed to examine the feasibility of digital discrimination of FDM composite signals, and of eliminating line frequency noises in data measurements.

Source record↗
NASA NTRS1982

A Method for Peat Inventory Based on LANDSAT Data and Computerized Mapping

Wetlands were preliminarily delineated on a geometrically-corrected color composite map printed from digital LANDSAT data using a computerized color plotting system. A digital classification was performed to identify the location and extent of wetland types (e.g., open bog, types of treed fen and black spruce-alder swamp). A map is printed from the results of this classification using the computerized color plotter. This color-coded map, produced at several different scales, provides a basis for pre-selecting field sampling sites. Helicopter-aided spot sampling based on the LANDSAT-derived map was conducted over the entire 1700 sq km area of North Ontario. Traditional transect sampling was carried out over a portion of the area, so that the two methods could be compared. Spot sampling based on the LANDSAT-derived map was found to produce results virtually identical to those produced by the transect sampling technique, in approximately one-fifteenth of the time and with a proportionate reduction in cost.

Pala, S.↗
NASA NTRS1988

Flight control systems development and flight test experience with the HiMAT research vehicles

Two highly maneuverable aircraft technology (HiMAT) remotely piloted vehicles were flown a total of 26 flights. These subscale vehicles were of advanced aerodynamic configuration with advanced technology concepts such as composite and metallic structures, digital integrated propulsion control, and ground (primary) and airborne (backup) relaxed static stability, digital fly-by-wire control systems. Extensive systems development, checkout, and flight qualification were required to conduct the flight test program. The design maneuver goal was to achieve a sustained 8-g turn at Mach 0.9 at an altitude of 25,000 feet. This goal was achieved, along with the acquisition of high-quality flight data at subsonic and supersonic Mach numbers. Control systems were modified in a variety of ways using the flight-determined aerodynamic characteristics. The HiMAT program was successfully completed with approximately 11 hours of total flight time.

Kempel, Robert W.↗
NASA NTRS1993

Digital data over video channels - Techniques for Spacelab

A study was made of various techniques for transmitting digital data over a composite video channel. Transmitting data from experiments on the Space Shuttle Orbiter over a video channel is attractive since extra channel capacity is needed. Broadcast television telecommunications schemes and other techniques described in the literature were reviewed and compared. PSK (Phase Shift Keying), MPSK (m-ary PSK), or PAM (Pulse Amplitude Modulation) can be transmitted on visible lines of a frame, unassigned lines of the VBI (Vertical Blanking Interval), or during the HBI (Horizontal Blanking Interval). All three modulation techniques can be attractive under the proper conditions. However, PAM on visible lines or during the VBI should be relatively easy to implement, provide adequate average data rates, and give acceptable BERs (Bit Error Rates).

Smith, Dean L.↗
NASA NTRS1993

Techniques for transmitting digital data on the Spacelab's analog video channel

A study was made of various techniques for transmitting digital data over a composite video channel. Transmitting data from experiments on the Space Shuttle Orbiter over a video channel is attractive since extra channel capacity is needed. Broadcast television telecommunications schemes and other techniques described in the literature were reviewed and compared. PSK (Phase Shift Keying), MPSK (m-ary PSK), or PAM (Pulse Amplitude Modulation) can be transmitted on visible lines of a frame, unassigned lines of the VBI (Vertical Blanking Interval), or during the HBI (Horizontal Blanking Interval). All three modulation techniques can be attractive under the proper conditions. However, PAM on visible lines or during the VBI should be relatively easy to implement, provide adequate average data rates, and give acceptable BERs (Bit Error Rates).

Smith, Dean L.↗
NASA NTRSDate not supplied

Design for Manufacturing of Structures with Automated Fiber Placement via Integration of Analysis and Process Planning

Under the Design for Manufacturing (DFM) task in the NASA HiCAM program, significant process has been made towards establishing a fully automated optimization process that spans the structural analysis, design, and manufacturing process planning for Automated Fiber Placement (AFP) structures. Previous efforts in this area established the data formats and mapping processes needed to exchange data between disciplines. The software tools used in the framework are HyperX (structural optimization), CAPP (process planning), and VCP (AFP path generation). The work has culminated with automation of data exchanges and an optimization process that drives the three software toward convergence. Within this framework, HyperX is used to generate mass-optimum composite designs which are iterated with VCP and CAPP to improve manufacturability of the designs. As the ply manufacturing process is adjusted by CAPP and VCP, HyperX continually re-assesses the structural integrity of the part and makes adjustments to the laminate as needed. For example, the position of fiber steering and tow overlaps/gaps can necessitate changes to the laminate design. Once the design converges, the end result is a stack of plies that meets both structural and manufacturing requirements. This paper presents the details of the framework and demonstrations the automated process on several parts with significant double-curvature.

HiCAM↗