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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Specification-based software sizing: An empirical investigation of function metrics

For some time the software industry has espoused the need for improved specification-based software size metrics. This paper reports on a study of nineteen recently developed systems in a variety of application domains. The systems were developed by a single software services corporation using a variety of languages. The study investigated several metric characteristics. It shows that: earlier research into inter-item correlation within the overall function count is partially supported; a priori function counts, in themself, do not explain the majority of the effort variation in software development in the organization studied; documentation quality is critical to accurate function identification; and rater error is substantial in manual function counting. The implication of these findings for organizations using function based metrics are explored.

Jeffery, Ross↗
NASA NTRS1994

Engine Structures Analysis Software: Component Specific Modeling (COSMO)

A component specific modeling software program has been developed for propulsion systems. This expert program is capable of formulating the component geometry as finite element meshes for structural analysis which, in the future, can be spun off as NURB geometry for manufacturing. COSMO currently has geometry recipes for combustors, turbine blades, vanes, and disks. Component geometry recipes for nozzles, inlets, frames, shafts, and ducts are being added. COSMO uses component recipes that work through neutral files with the Technology Benefit Estimator (T/BEST) program which provides the necessary base parameters and loadings. This report contains the users manual for combustors, turbine blades, vanes, and disks.

Mcknight, R. L.↗
NASA NTRS1995

Surface cleanliness of fluid systems, specification for

This specification establishes surface cleanliness levels, test methods, cleaning and packaging requirements, and protection and inspection procedures for determining surface cleanliness. These surfaces pertain to aerospace parts, components, assemblies, subsystems, and systems in contact with any fluid medium.

Source record↗
NASA NTRS1995

Lower body negative pressure chamber: Design and specifications for tilt-table mounting

Specifications for a lower body negative pressure chamber for mounting on a tilting table are presented. The main plate is made from HEXEL honeycomb board 1.0 inch thick. The plate, supported at three edges, will be subjected to a uniform pressure differential of -4.7 lb/sq in. A semi-cylindrical Plexiglass top (chamber) is attached to the main plate; the pressure within the chamber will be about 10lb/sq in during operation. The stresses incurred by the main plate with this partial vacuum were calculated. All linear dimensions are in inches.

Salamacha, Laura↗
NASA NTRS1995

Reliable multicast protocol specifications protocol operations

This appendix contains the complete state tables for Reliable Multicast Protocol (RMP) Normal Operation, Multi-RPC Extensions, Membership Change Extensions, and Reformation Extensions. First the event types are presented. Afterwards, each RMP operation state, normal and extended, is presented individually and its events shown. Events in the RMP specification are one of several things: (1) arriving packets, (2) expired alarms, (3) user events, (4) exceptional conditions.

Callahan, John R.↗
NASA NTRS1995

Reliable multicast protocol specifications flow control and NACK policy

This appendix presents the flow and congestion control schemes recommended for RMP and a NACK policy based on the whiteboard tool. Because RMP uses a primarily NACK based error detection scheme, there is no direct feedback path through which receivers can signal losses through low buffer space or congestion. Reliable multicast protocols also suffer from the fact that throughput for a multicast group must be divided among the members of the group. This division is usually very dynamic in nature and therefore does not lend itself well to a priori determination. These facts have led the flow and congestion control schemes of RMP to be made completely orthogonal to the protocol specification. This allows several differing schemes to be used in different environments to produce the best results. As a default, a modified sliding window scheme based on previous algorithms are suggested and described below.

Callahan, John R.↗
NASA NTRS1996

Applications of Formal Methods to Specification and Safety of Avionics Software

This report treats several topics in applications of formal methods to avionics software development. Most of these topics concern decision tables, an orderly, easy-to-understand format for formally specifying complex choices among alternative courses of action. The topics relating to decision tables include: generalizations fo decision tables that are more concise and support the use of decision tables in a refinement-based formal software development process; a formalism for systems of decision tables with behaviors; an exposition of Parnas tables for users of decision tables; and test coverage criteria and decision tables. We outline features of a revised version of ORA's decision table tool, Tablewise, which will support many of the new ideas described in this report. We also survey formal safety analysis of specifications and software.

Hoover, D. N.↗
NASA NTRS1996

An introduction to requirements capture using PVS: Specification of a simple autopilot

This paper presents an introduction to capturing software requirements in the PVS formal language. The object of study is a simplified digital autopilot that was motivated in part by the mode control panel of NASA Langley's Boeing 737 research aircraft. The paper first presents the requirements for this autopilot in English and then steps the reader through a translation of these requirements into formal mathematics. Along the way deficiencies in the English specification are noted and repaired. Once completed, the formal PVS requirement is analyzed using the PVS theorem prover and shown to maintain an invariant over its state space.

Butler, Ricky W.↗
NASA NTRS1996

Design Specification for a Thrust-Vectoring, Actuated-Nose-Strake Flight Control Law for the High-Alpha Research Vehicle

Specifications for a flight control law are delineated in sufficient detail to support coding the control law in flight software. This control law was designed for implementation and flight test on the High-Alpha Research Vehicle (HARV), which is an F/A-18 aircraft modified to include an experimental multi-axis thrust-vectoring system and actuated nose strakes for enhanced rolling (ANSER). The control law, known as the HARV ANSER Control Law, was designed to utilize a blend of conventional aerodynamic control effectors, thrust vectoring, and actuated nose strakes to provide increased agility and good handling qualities throughout the HARV flight envelope, including angles of attack up to 70 degrees.

Bacon, Barton J.↗
NASA NTRS1997

Generic Airplane Model Concept and Four Specific Models Developed for Use in Piloted Simulation Studies

A generic airplane model concept was developed to allow configurations with various agility, performance, handling qualities, and pilot vehicle interface to be generated rapidly for piloted simulation studies. The simple concept allows stick shaping and various stick command types or modes to drive an airplane with both linear and nonlinear components. Output from the stick shaping goes to linear models or a series of linear models that can represent an entire flight envelope. The generic model also has provisions for control power limitations, a nonlinear feature. Therefore, departures from controlled flight are possible. Note that only loss of control is modeled, the generic airplane does not accurately model post departure phenomenon. The model concept is presented herein, along with four example airplanes. Agility was varied across the four example airplanes without altering specific excess energy or significantly altering handling qualities. A new feedback scheme to provide angle-of-attack cueing to the pilot, while using a pitch rate command system, was implemented and tested.

Hoffler, Keith D.↗
NASA NTRS1998

Space Station Cathode Design, Performance, and Operating Specifications

A plasma contactor system was baselined for the International Space Station (ISS) to eliminate/mitigate damaging interactions with the space environment. The system represents a dual-use technology which is a direct outgrowth of the NASA electric propulsion program and, in particular, the technology development efforts on ion thruster systems. The plasma contactor includes a hollow cathode assembly (HCA), a power electronics unit, and a xenon gas feed system. Under a pre-flight development program, these subsystems were taken to the level of maturity appropriate for transfer to U.S. industry for final development. NASA's Lewis Research Center was subsequently requested by ISS to manufacture and deliver the engineering model, qualification model, and flight HCA units. To date, multiple units have been built. One cathode has demonstrated approximately 28,000 hours lifetime, two development unit HCAs have demonstrated over 10,000 hours lifetime, and one development unit HCA has demonstrated more than 32,000 ignitions. All 8 flight HCAs have been manufactured, acceptance tested, and are ready for delivery to the flight contractor. This paper discusses the requirements, mechanical design, performance, operating specifications, and schedule for the plasma contactor flight HCAs.

Patterson, Michael J.↗
NASA NTRS1995

Constant-Pressure Specific Heat to Hemispherical Total Emissivity Ratio for Undercooled Liquid Nickel, Zirconium, and Silicon

Radiative cooling curves of nickel, zirconium, and silicon melts that were obtained using the high-temperature, high-vacuum electrostatic levitator (HTHVESL) have been analyzed to determine the ratio between the constant-pressure specific heat and the hemispherical total emissivity, c(sub p)(T)epsilon(sub T)(T). This ratio determined over a wide liquid temperature range for each material allows us to determine c(sub p)(T) if epsilon(sub T)(T) is known or vice versa. Following the recipe, the hemi-spherical total emissivities for each sample at its melting temperature, epsilon(sub T)(T(sub M)), have been determined using c(sub p)(T(sub m)) values available in the literature. They are 0.15, 0.29, and 0.17, for Ni, Zr, and Si, respectively.

Rulison, Aaron J.↗
NASA NTRS1999

NDE Process Development Specification for SRB Composite Nose Cap

The Shuttle Upgrade program is a continuing improvement process to enable the Space Shuttle to be an effective space transportation vehicle for the next few decades. The Solid Rocket Booster (SRB), as a component of that system, is currently undergoing such an improvement. Advanced materials, such as composites, have given us a chance to improve performance and to reduce weight. The SRB Composite Nose Cap (CNC) program aims to replace the current aluminum nose cap, which is coated with a Thermal Protection System and poses a possible debris hazard, with a lighter, stronger, CNC. For the next 2 years, this program will evaluate the design, material selection, properties, and verification of the CNC. This particular process specification cites the methods and techniques for verifying the integrity of such a nose cap with nondestructive evaluation.

Suits, M.↗
NASA NTRS1997

Magnetic flux in modeled magnetic clouds at 1 AU and some specific comparisons to associated photospheric flux

In order to better understand the solar origins of magnetic clouds, statistical distributions of the estimated axial magnetic flux of 30 magnetic clouds at 1 AU, separated according to their occurrence during the solar cycle, were obtained and a comparison was made of the magnetic flux of a magnetic cloud to the aggregate flux of apparently associated photospheric magnetic flux tubes, for some specific cases. The 30 magnetic clouds comprise 12 cases from WIND, and the remainder from IMP-8, earlier IMPs, the International Sun-Earth Explorer (ISEE) 3 and HELIOS. The total magnetic flux along the cloud axis was estimated using a constant alpha, cylindrical, force-free flux rope model to determine cloud diameter and axial magentic field strength. The distribution of magentic fluxes for the 30 clouds is shown to be in the form of a skewed Gaussian.

Lepping, R. P.↗
NASA NTRS1997

Specific Volumes of the Zr(41.2)Ti(13.8)Cu(12.5)Ni(10.0)Be(22.5) Alloy in the Liquid, Glass, and Crystalline States

The specific volumes of the Zr(41.2)Ti(3.8)Cu(2.5)Ni(10.0)Be(22.5) alloy as a function of temperature, T, are determined by employing an image digitizing technique and numerical calculation methods applied to the electrostatically levitated spherical alloy. The linear fitting of the volumes of the alloy in the liquid, V(sub l), glass, V(sub g) and crystalline V(sub c), states in the temperature ranges shown in parentheses are V(sub l)(T) = 0.1583 + 8.877 x 10(exp -6) T(cu cm/g) (700-1300 K);V(sub g)(T) = 0.1603 + 5.528 x 10(exp -6) T (400-550 K);V(sub c)(T) = 0.1583 + 6.21 x 10(exp -6)T(400-850 K). The average volume thermal expansion coefficients within the temperature ranges are determined to be 5.32, 3.39. and 3.83 x 10(exp -5) (1/K) for the liquid, glass, and crystalline states, respectively.

Ohsaka, K.↗
NASA NTRS1995

Intent Specifications

We have been investigating the implications of using abstractions based on intent rather than the aggregation and information-hiding abstractions commonly used in software en- gineering: Cognitive psychologists have shown that intent abstraction is consistent with human problem-solving processes. We believe that new types of specifications and designs based on this concept can assist in understanding and specifying requirements, capturing the most important design rationale information in an efficient and economical way, and supporting the process of identifying and analyzing required changes to minimize the introduction of errors. The goal of hierarchical abstraction is to allow both top-down and bottom-up reasoning about a complex system. In computer science, we have made much use of (1) part-whole abstractions where each level of a hierarchy represents an aggregation of the components at a lower level and of (2) information-hiding abstractions where each level contains the same conceptual information but hides some details about the concepts, that is, each level is a refinement of the information at a higher level.

Leveson, Nancy G.↗