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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Integrity Constraint Monitoring in Software Development: Proposed Architectures

In the development of complex software systems, designers are required to obtain from many sources and manage vast amounts of knowledge of the system being built and communicate this information to personnel with a variety of backgrounds. Knowledge concerning the properties of the system, including the structure of, relationships between and limitations of the data objects in the system, becomes increasingly more vital as the complexity of the system and the number of knowledge sources increases. Ensuring that violations of these properties do not occur becomes steadily more challenging. One approach toward managing the enforcement or system properties, called context monitoring, uses a centralized repository of integrity constraints and a constraint satisfiability mechanism for dynamic verification of property enforcement during program execution. The focus of this paper is to describe possible software architectures that define a mechanism for dynamically checking the satisfiability of a set of constraints on a program. The next section describes the context monitoring approach in general. Section 3 gives an overview of the work currently being done toward the addition of an integrity constraint satisfiability mechanism to a high-level program language, SequenceL, and demonstrates how this model is being examined to develop a general software architecture. Section 4 describes possible architectures for a general constraint satisfiability mechanism, as well as an alternative approach that, uses embedded database queries in lieu of an external monitor. The paper concludes with a brief summary outlining the, current state of the research and future work.

Fernandez, Francisco G.↗
NASA NTRS1990

Reproduction in the space environment: Part II. Concerns for human reproduction

Long-duration space flight and eventual colonization of our solar system will require successful control of reproductive function and a thorough understanding of factors unique to space flight and their impact on gynecologic and obstetric parameters. Part II of this paper examines the specific environmental factors associated with space flight and the implications for human reproduction. Space environmental hazards discussed include radiation, alteration in atmospheric pressure and breathing gas partial pressures, prolonged toxicological exposure, and microgravity. The effects of countermeasures necessary to reduce cardiovascular deconditioning, calcium loss, muscle wasting, and neurovestibular problems are also considered. In addition, the impact of microgravity on male fertility and gamete quality is explored. Due to current constraints, human pregnancy is now contraindicated for space flight. However, a program to explore effective countermeasures to current constraints and develop the required health care delivery capability for extended-duration space flight is suggested. A program of Earth- and space-based research to provide further answers to reproductive questions is suggested.

Review, Tutorial↗
NASA NTRS2015

Improvements in Modeling Thruster Plume Erosion Damage to Spacecraft Surfaces

Spacecraft bipropellant thrusters impact spacecraft surfaces with high speed droplets of unburned and partially burned propellant. These impacts can produce erosion damage to optically sensitive hardware and systems (e.g., windows, camera lenses, solar cells and protective coatings). On the International Space Station (ISS), operational constraints are levied on the position and orientation of the solar arrays to mitigate erosion effects during thruster operations. In 2007, the ISS Program requested evaluation of erosion constraint relief to alleviate operational impacts due to an impaired Solar Alpha Rotary Joint (SARJ). Boeing Space Environments initiated an activity to identify and remove sources of conservatism in the plume induced erosion model to support an expanded range of acceptable solar array positions  The original plume erosion model over-predicted plume erosion and was adjusted to better correlate with flight experiment results. This paper discusses findings from flight experiments and the methodology employed in modifying the original plume erosion model for better correlation of predictions with flight experiment data. The updated model has been successful employed in reducing conservatism and allowing for enhanced flexibility in ISS solar array operations.

Soares, Carlos↗
NASA NTRS1977

Computer assistance for the structural chemist

A description is presented of the approaches used to modify the molecular structure generator program, CONGEN. The CONGEN program for constructing structures under constraints has been discussed by Carhart et al. (1975). The modifications reported are to lead to a more efficient structure generation on the basis of a translation of structural data input to the program. From an algorithmic standpoint, CONGEN is successful if it can, in a reasonable amount of time and without exhausting storage resources, produce a list of candidate structures satisfying the chemist's constraints. However, this list is often quite large, and it remains for the chemist to discriminate among the candidates, eventually reducing the possibilities to just one structure. Ways are studied for providing computer assistance in examining and further constraining lists of structural candidates.

Carhart, R. E.↗
NASA NTRS1988

A flexible computer aid for conceptual design based on constraint propagation and component-modeling

The Rubber Airplane program, which combines two symbolic processing techniques with a component-based database of design knowledge, is proposed as a computer aid for conceptual design. Using object-oriented programming, programs are organized around the objects and behavior to be simulated, and using constraint propagation, declarative statements designate mathematical relationships among all the equation variables. It is found that the additional level of organizational structure resulting from the arrangement of the design information in terms of design components provides greater flexibility and convenience.

Kolb, Mark A.↗
NASA NTRS1995

Planning Complex Projects Automatically

Automated Manifest Planner (AMP) computer program applies combination of artificial-intelligence techniques to assist both expert and novice planners, reducing planning time by orders of magnitude. Gives planners flexibility to modify plans and constraints easily, without need for programming expertise. Developed specifically for planning space shuttle missions 5 to 10 years ahead, with modifications, applicable in general to planning other complex projects requiring scheduling of activities depending on other activities and/or timely allocation of resources. Adaptable to variety of complex scheduling problems in manufacturing, transportation, business, architecture, and construction.

Henke, Andrea L.↗
NASA NTRS2000

A Mars Exploration Discovery Program

The Mars Exploration Program should consider following the Discovery Program model. In the Discovery Program a team of scientists led by a PI develop the science goals of their mission, decide what payload achieves the necessary measurements most effectively, and then choose a spacecraft with the capabilities needed to carry the payload to the desired target body. The primary constraints associated with the Discovery missions are time and money. The proposer must convince reviewers that their mission has scientific merit and is feasible. Every Announcement of Opportunity has resulted in a collection of creative ideas that fit within advertised constraints. Following this model, a "Mars Discovery Program" would issue an Announcement of Opportunity for each launch opportunity with schedule constraints dictated by the launch window and fiscal constraints in accord with the program budget. All else would be left to the proposer to choose, based on the science the team wants to accomplish, consistent with the program theme of "Life, Climate and Resources". A proposer could propose a lander, an orbiter, a fleet of SCOUT vehicles or penetrators, an airplane, a balloon mission, a large rover, a small rover, etc. depending on what made the most sense for the science investigation and payload. As in the Discovery program, overall feasibility relative to cost, schedule and technology readiness would be evaluated and be part of the selection process.

Hansen, C. J.↗
NASA NTRS1987

System engineering techniques for establishing balanced design and performance guidelines for the advanced telerobotic testbed

Novel system engineering techniques have been developed and applied to establishing structured design and performance objectives for the Telerobotics Testbed that reduce technical risk while still allowing the testbed to demonstrate an advancement in state-of-the-art robotic technologies. To estblish the appropriate tradeoff structure and balance of technology performance against technical risk, an analytical data base was developed which drew on: (1) automation/robot-technology availability projections, (2) typical or potential application mission task sets, (3) performance simulations, (4) project schedule constraints, and (5) project funding constraints. Design tradeoffs and configuration/performance iterations were conducted by comparing feasible technology/task set configurations against schedule/budget constraints as well as original program target technology objectives. The final system configuration, task set, and technology set reflected a balanced advancement in state-of-the-art robotic technologies, while meeting programmatic objectives and schedule/cost constraints.

Zimmerman, W. F.↗
NASA NTRS1989

Compendium of small class ELV capabilities, costs, and constraints

Both NASA and DARPA are investigating programs to provide flight demonstration opportunities for new commercially developed rockets. Development of such rockets will be decisive for the success of expendable launch vehicle (ELV) commercialization. The costs and capabilities associated with the various vehicles are discussed here, emphasizing the constraints on their development and widespread utilization. An overview is presented of related international launch vehicle development plans, and the market for small ELVs in the 1990s is discussed.

Poniatowski, Karen S.↗
NASA NTRS1987

The detection of planetary systems from Space Station - A star observation strategy

A 10-20-yr star-observation program for the Space Station Astrometric Telescope Facility (ATF) is proposed and evaluated by means of computer simulations. The primary aim of the program is to detect stars with planetary systems by precise determination of their motion relative to reference stars. The designs proposed for the ATF are described and illustrated; the basic parameters of the 127 stars selected for the program are listed in a table; spacecraft and science constraints, telescope slewing rates, and the possibility of limiting the program sample to stars near the Galactic equator are discussed; and the effects of these constraints are investigated by simulating 1 yr of ATF operation. Viewing all sky regions, the ATF would have 81-percent active viewing time, observing each star about 200 times (56 h) per yr; only small decrements in this performance would result from limiting the viewing field.

Mascy, Alfred C.↗
NASA NTRS1975

Solar electric geocentric transfer with attitude constraints: Analysis

A time optimal or nearly time optimal trajectory program was developed for solar electric geocentric transfer with or without attitude constraints and with an optional initial high thrust stage. The method of averaging reduces computation time. A nonsingular set of orbital elements is used. The constraints, which are those of one of the SERT-C designs, introduce complexities into the analysis and the solution yields possible discontinuous changes in thrust direction. The power degradation due to VanAllen radiation is modeled analytically. A wide range of solar cell characteristics is assumed. Effects such as oblateness and shadowing are included. The analysis and the results of many example runs are included.

Sackett, L. L.↗
NASA NTRS2005

Knowledge Capture and Management for Space Flight Systems

The incorporation of knowledge capture and knowledge management strategies early in the development phase of an exploration program is necessary for safe and successful missions of human and robotic exploration vehicles over the life of a program. Following the transition from the development to the flight phase, loss of underlying theory and rationale governing design and requirements occur through a number of mechanisms. This degrades the quality of engineering work resulting in increased life cycle costs and risk to mission success and safety of flight. Due to budget constraints, concerned personnel in legacy programs often have to improvise methods for knowledge capture and management using existing, but often sub-optimal, information technology and archival resources. Application of advanced information technology to perform knowledge capture and management would be most effective if program wide requirements are defined at the beginning of a program.

Goodman, John L.↗
NASA NTRS2012

A Linear Programming Approach to the Development of Contrail Reduction Strategies Satisfying Operationally Feasible Constraints

A class of strategies has been proposed to reduce contrail formation in the United States airspace. A 3D grid based on weather data and the cruising altitude level of aircraft is adjusted to avoid the persistent contrail potential area with the consideration to fuel-efficiency. In this paper, the authors introduce a contrail avoidance strategy on 3D grid by considering additional operationally feasible constraints from an air traffic controller's aspect. First, shifting too many aircraft to the same cruising level will make the miles-in-trail at this level smaller than the safety separation threshold. Furthermore, the high density of aircraft at one cruising level may exceed the workload for the traffic controller. Therefore, in our new model we restrict the number of total aircraft at each level. Second, the aircraft count variation for successive intervals cannot be too drastic since the workload to manage climbing/descending aircraft is much larger than managing cruising aircraft. The contrail reduction is formulated as an integer-programming problem and the problem is shown to have the property of total unimodularity. Solving the corresponding relaxed linear programming with the simplex method provides an optimal and integral solution to the problem. Simulation results are provided to illustrate the methodology.

Wei, Peng↗
NASA NTRS2001

Complete ISOPHOT (C200) Maps of a Nearby Prototypical GMC: W3 (Spring) or NGC7538 (Fall)

We were originally awarded Priority 3 time (approximately 60,000 sec) with Infrared Space Observatory (ISO) to obtain a complete ISOPHOT (PHT32-C200) map of a nearby prototypical giant molecular cloud (GMC). Following the FALL launch and revised estimates for the sensitivity of the ISOPHOT detectors, our program was modified to fit within the time constraints while still carrying out the main science requirements. The revised program requested long strip maps of our FALL target (NGC7538) using sequences of PHT37/38/39 observations with LWS observations of the brightest regions. The large number of AOTs required to cover each GMC required that our observations be spread over four separate proposals (PROP-01, PROP-02, PROP-03, PROP-04) which together comprise a single observing program. Our program was executed in early 1997; nearly 50,000 sec of data were obtained, including all of our requested ISOPHOT C200 observations. None of the LWS data were taken.

Sanders, David B.↗
NASA NTRS1976

A new era of space transportation

It is pointed out that founded on the experiences of Apollo, Skylab, and the Apollo/Soyuz mission an era is entered which will be characterized by a displacement of the interface between the experimenter and his experiment from the control center on the ground to the laboratory in orbit. A new world has been opened by going into space. Economic applications are related to the achievement of an enormous efficiency in world communications at a much lower cost. However, programs of space exploration and usage are under severe economic constraints. A primary tool to lower the cost of programs is to be the Space Transportation System using the Space Shuttle. It is emphasized that the Shuttle system is an international enterprise. Attention is also given to the results of the Viking missions, the Landsat satellites, and applications of space technology for science and commerce.

Fletcher, J. C.↗
NASA NTRS1985

Human productivity program definition

The optimization of human productivity on the space station within the existing resources and operational constraints is the aim of the Human Productivity Program. The conceptual objectives of the program are as follows: (1) to identify long lead technology; (2) to identify responsibility for work elements; (3) to coordinate the development of crew facilities and activities; and (4) to lay the foundation for a cost effective approach to improving human productivity. Human productivity work elements are also described and examples are presented.

Cramer, D. B.↗
NASA NTRS1975

Preliminary mission planning using Interactive Graphics

The selection of satellite orbits, subject to mission and launch vehicle constraints, can be expedited using the IGOS (Interactive Graphics Orbit Selection) computer program. The program operates in a conversational mode displaying the constraints as shaded areas on a graphics terminal. Mission requirements evaluated include: earth observation coverage, radiation environment, orbit lifetime, and sun synchronization. Launch vehicle constraints consist of injection accuracy and payload capability and include the impact of launch site, and launch azimuth restrictions. Sample output is shown, the hardware and software configurations are described, and details of the mathematical model are summarized.

Rea, F. G.↗