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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Thematic mapper image quality - Preliminary results

Based on images analyzed so far, the band to band registration accuracy of the thematic mapper is very good. For bands within the same focal plane, the mean misregistrations are well within the specification, 0.2 pixels. For bands between the cooled and uncooled focal planes, there is a consistent mean misregistration of 0.5 pixels along-scan and 0.2-0.3 pixels across-scan. It exceeds the permitted 0.3 pixels for registration of bands between focal planes. If the mean misregistrations were removed by the data processing software, an analysis of the standard deviation of the misregistration indicates all band combinations would meet the registration specifications except for those including the thermal band. Analysis of the periodic noise in one image indicates a noise component in band 1 with a spatial frequency equivalent to 3.2 pixels in the along-scan direction.

Wrigley, R. C.↗
NASA NTRS1984

An interactive program for software reliability modeling

With the tremendous growth in computer software, the demand has arisen for producing cost effective reliable software. Over the last 10 years an area of research has developed which attempts to address this problem by estimating a program's current reliability by modeling either the times between error detections or the error counts in past testing periods. A new tool for interactive software reliability analysis using the computer is described. This computer program allows the user to perform a complete reliability analysis using any of eight well-known models appearing in the literature. Some of the capabilities of the program are illustrated by means of an analysis of a set of simulated error data.

Farr, W. H.↗
NASA NTRS1985

International Ultraviolet Explorer Observatory operations

This volume contains the final report for the International Ultraviolet Explorer IUE Observatory Operations contract. The fundamental operational objective of the International Ultraviolet Explorer (IUE) program is to translate competitively selected observing programs into IUE observations, to reduce these observations into meaningful scientific data, and then to present these data to the Guest Observer in a form amenable to the pursuit of scientific research. The IUE Observatory is the key to this objective since it is the central control and support facility for all science operations functions within the IUE Project. In carrying out the operation of this facility, a number of complex functions were provided beginning with telescope scheduling and operation, proceeding to data processing, and ending with data distribution and scientific data analysis. In support of these critical-path functions, a number of other significant activities were also provided, including scientific instrument calibration, systems analysis, and software support. Routine activities have been summarized briefly whenever possible.

Source record↗
NASA NTRS1987

Integrated Analysis Capability Program

Integrated Analysis Capability (IAC) software system provides highly effective, interactive analysis tool for integrated design of large structures. Developed to serve as interface for programs from fields of structures, thermodynamics, controls, and system dynamics with executive system and data base to yield highly-efficient multidisciplinary system. Written in FORTRAN 77.

Frisch, Harold P.↗
NASA NTRS1987

Software safety

Software safety and its relationship to other qualities are discussed. It is shown that standard reliability and fault tolerance techniques will not solve the safety problem for the present. A new attitude requires: looking at what you do NOT want software to do along with what you want it to do; and assuming things will go wrong. New procedures and changes to entire software development process are necessary: special software safety analysis techniques are needed; and design techniques, especially eliminating complexity, can be very helpful.

Leveson, Nancy↗
NASA NTRS1993

Calibration Of NASA/JPL DC-8 SAR Data

Report describes recent improvements in calibration of data gathered by polarimetric synthetic-aperture-radar (SAR) system operated by NASA's Jet Propulsion Laboratory. Improvements are: relocation of calibration site; JPL POLCAL software; and ANTENCAL software. Presents analysis of calibration performance over number of sites during years 1989 and 1990.

Freeman, Anthony↗
NASA NTRS1993

Computational Controls Workstation: Algorithms and hardware

The Computational Controls Workstation provides an integrated environment for the modeling, simulation, and analysis of Space Station dynamics and control. Using highly efficient computational algorithms combined with a fast parallel processing architecture, the workstation makes real-time simulation of flexible body models of the Space Station possible. A consistent, user-friendly interface and state-of-the-art post-processing options are combined with powerful analysis tools and model databases to provide users with a complete environment for Space Station dynamics and control analysis. The software tools available include a solid modeler, graphical data entry tool, O(n) algorithm-based multi-flexible body simulation, and 2D/3D post-processors. This paper describes the architecture of the workstation while a companion paper describes performance and user perspectives.

Venugopal, R.↗
NASA NTRS1994

Photospheric origins of chromospheric and coronal activity

This contract is for a two-year research study of the origins of activity in the upper atmosphere of the sun. The approach is to collect high resolution images of the lower atmosphere on observing runs at the Swedish Solar Observatory on La Palma, Canary Islands, Spain. The best observations are analyzed and compared with data from other telescopes and/or theoretical models, to study magnetic flux emergence, coronal heating, and various dynamic phenomena and transients. Software for analysis and visualization of the data is developed as needed. The contract is being performed by the Solar and Astrophysics Laboratory, part of the Lockheed Palo Alto Research Laboratory (LPARL) of the Research and Development Division (RDD) of Lockheed Missiles and Space Co., Inc. (LMSC).

Tarbell, Theodore↗
NASA NTRS1994

Study of the kinematic and dynamic characteristics of a wormgear transmission for helicopter applications

The first phase of the study of the performance of a wormgear transmission is reported. In this phase the work included the selection of a double-enveloping wormgear type, and its dimensions, suitable for use in helicopter transmissions; the 3-D graphics representation of the selected wormgear using the I-DEAS software; the analysis of the kinematics of meshing; the analysis of load sharing among the meshing teeth; and the implementation of the analyses in a computer program. The report describes the analyses, their results, and the use of the computer programs.

Sun, D. C.↗
NASA NTRS1994

In search of Nemesis

The parallax of all stars of visual magnitude greater than about 6.5 has already been measured. If Nemesis is a main-sequence star 1 parsec away, this requires Nemesis's mass to be less than about 0.4 solar masses. If it were less than about 0.05 solar masses its gravity would be too weak to trigger a comet storm. If Nemesis is on the main sequence, this mass range requires it to be a red dwarf. A red dwarf companion would probably have been missed by standard astronomical surveys. Nearby stars are usually found because they are bright or have high proper motion. However, Nemesis's proper motion would now be 0.01 arcsec/yr, and if it is a red dwarf its magnitude is about 10 - too dim to attract attention. Unfortunately, standard four-color photometry does not distinguish between red dwarfs and giants. So although surveys such as the Dearborn Red Star Catalog list stars by magnitude and spectral type, they do not identify the dwarfs. Every star of the correct spectral type and magnitude must be scrutinized. Our candidate list is a hybrid; candidate red stars are identified in the astrometrically poor Dearborn Red Star Catalog and their positions are corrected using the Hubble Guide Star Catalog. When errors in the Dearborn catalog make it impossible to identify the corresponding Hubble star, the fields are split so that we have one centering on each possible candidate. We are currently scrutinizing 3098 fields, which we believe contain all possible red dwarf candidates in the northern hemisphere. Since our last report the analysis and database software has been completely rebuilt to take advantage of updated hardware, to make the data more accessible, and to implement improved methods of data analysis. The software is now completed and we are eliminating stars every clear night.

Carlson, S.↗
NASA NTRS1994

Domain analysis for the reuse of software development experiences

We need to be able to learn from past experiences so we can improve our software processes and products. The Experience Factory is an organizational structure designed to support and encourage the effective reuse of software experiences. This structure consists of two organizations which separates project development concerns from organizational concerns of experience packaging and learning. The experience factory provides the processes and support for analyzing, packaging, and improving the organization's stored experience. The project organization is structured to reuse this stored experience in its development efforts. However, a number of questions arise: What past experiences are relevant? Can they all be used (reused) on our current project? How do we take advantage of what has been learned in other parts of the organization? How do we take advantage of experience in the world-at-large? Can someone else's best practices be used in our organization with confidence? This paper describes approaches to help answer these questions. We propose both quantitative and qualitative approaches for effectively reusing software development experiences.

Basili, V. R.↗
NASA NTRS1996

The Michelson Stellar Interferometer Error Budget for Triple Triple-Satellite Configuration

This report presents the results of a study of the instrumentation tolerances for a conventional style Michelson stellar interferometer (MSI). The method used to determine the tolerances was to determine the change, due to the instrument errors, in the measured fringe visibility and phase relative to the ideal values. The ideal values are those values of fringe visibility and phase that would be measured by a perfect MSI and are attributable solely to the object being detected. Once the functional relationship for changes in visibility and phase as a function of various instrument errors is understood it is then possible to set limits on the instrument errors in order to ensure that the measured visibility and phase are different from the ideal values by no more than some specified amount. This was done as part of this study. The limits we obtained are based on a visibility error of no more than 1% and a phase error of no more than 0.063 radians (this comes from 1% of 2(pi) radians). The choice of these 1% limits is supported in the literture. The approach employed in the study involved the use of ASAP (Advanced System Analysis Program) software provided by Breault Research Organization, Inc., in conjunction with parallel analytical calculations. The interferometer accepts object radiation into two separate arms each consisting of an outer mirror, an inner mirror, a delay line (made up of two moveable mirrors and two static mirrors), and a 10:1 afocal reduction telescope. The radiation coming out of both arms is incident on a slit plane which is opaque with two openings (slits). One of the two slits is centered directly under one of the two arms of the interferometer and the other slit is centered directly under the other arm. The slit plane is followed immediately by an ideal combining lens which images the radiation in the fringe plane (also referred to subsequently as the detector plane).

Marathay, Arvind S.↗
NASA NTRS1996

Current Results and Proposed Activities in Microgravity Fluid Dynamics

The Institute for Problems in Mechanics' Laboratory work in mathematical and physical modelling of fluid mechanics develops models, methods, and software for analysis of fluid flow, instability analysis, direct numerical modelling and semi-empirical models of turbulence, as well as experimental research and verification of these models and their applications in technological fluid dynamics, microgravity fluid mechanics, geophysics, and a number of engineering problems. This paper presents an overview of the results in microgravity fluid dynamics research during the last two years. Nonlinear problems of weakly compressible and compressible fluid flows are discussed.

Polezhaev, V. I.↗
NASA NTRS2001

Synthesizing Dynamic Programming Algorithms from Linear Temporal Logic Formulae

The problem of testing a linear temporal logic (LTL) formula on a finite execution trace of events, generated by an executing program, occurs naturally in runtime analysis of software. We present an algorithm which takes an LTL formula and generates an efficient dynamic programming algorithm. The generated algorithm tests whether the LTL formula is satisfied by a finite trace of events given as input. The generated algorithm runs in linear time, its constant depending on the size of the LTL formula. The memory needed is constant, also depending on the size of the formula.

Rosu, Grigore↗
NASA NTRS1994

Analysis and Optimization of Parallel Software Pipeline Performance

Pipelining is a common strategy for extracting parallelism from a collection of independent computational tasks, each of which is spread among a number of processors and has an implied data dependence. When implemented on MIMD parallel computers with finite process interrupt times, pipeline algorithms suffer from slowdown--in addition to the expected pipeline fill time--due to a wave-like propagation of delays. This phenomenon, which has been observed experimentally using the performance monitoring system AIMS, is investigated analytically, and an optimal correction is derived to eliminate the wave. Efficiency increase through the correction is verified experimentally.

VanderWijngaart, Rob F.↗
NASA NTRS2002

Synthesizing Monitors for Safety Properties

The problem of testing a linear temporal logic (LTL) formula on a finite execution trace of events, generated by an executing program, occurs naturally in time analysis of software. An algorithm which takes a past time LTL formula and generates an efficient dynamic programming algorithm is presented. The generated algorithm tests whether the formula is satisfied by a finite trace of events given as input and runs in linear time, its constant depending on the size of the LTL formula. The memory needed is constant, also depending on the size of the formula. Further optimizations of the algorithm are suggested. Past time operators suitable for writing succinct specifications axe introduced and shown definitionally equivalent to the standard operators. This work is part of the PathExplorer project, the objective of which it is to construct a flexible framework for monitoring and analyzing program executions.

Havelund, Klaus↗
NASA NTRS1996

Formalizing New Navigation Requirements for NASA's Space Shuttle

We describe a recent NASA-sponsored pilot project intended to gauge the effectiveness of using formal methods in Space Shuttle software requirements analysis. Several Change Requests (CRs) were selected as promising targets to demonstrate the utility of formal methods in this demanding application domain. A CR to add new navigation capabilities to the Shuttle, based on Global Positioning System (GPS) technology, is the focus of this industrial usage report. Portions of the GPS CR were modeled using the language of SRI's Prototype Verification System (PVS). During a limited analysis conducted on the formal specifications, numerous requirements issues were discovered. We present a summary of these encouraging results and conclusions we have drawn from the pilot project.

DiVito, Ben L.↗
NASA NTRS1991

Improving the Software Development Process Using Testability Research

Software testability is the the tendency of code to reveal existing faults during random testing. This paper proposes to take software testability predictions into account throughout the development process. These predictions can be made from formal specifications, design documents, and the code itself. The insight provided by software testability is valuable during design, coding, testing, and quality assurance. We further believe that software testability analysis can play a crucial role in quantifying the likelihood that faults are not hiding after testing does not result in any failures for the current version.

Voas, Jeffrey M.↗