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All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Visualization of IACG data

The common data format (CDF), adopted by the international solar terrestrial physics (ISTP) program and the Interagency Consultative Group (IACG), is considered. Extensive data sharing and data analysis are needed to ensure the success of the ISTP/IACG program. The CDF user guidelines and tools for creation, visualization and manipulation are underlined. Computer software applications based on CDF data sets and designed using ISTP/IACG guidelines are shown.

Kessel, Ramona L.↗
NASA NTRS1998

Spread Spectrum Receiver Electromagnetic Interference (EMI) Test Guide

The objective of this test guide is to document appropriate unit level test methods and techniques for the performance of EMI testing of Direct Sequence (DS) spread spectrum receivers. Consideration of EMI test methods tailored for spread spectrum receivers utilizing frequency spreading, techniques other than direct sequence (such as frequency hopping, frequency chirping, and various hybrid methods) is beyond the scope of this test guide development program and is not addressed as part of this document EMI test requirements for NASA programs are primarily developed based on the requirements contained in MIL-STD-46 1 D (or earlier revisions of MIL-STD-46 1). The corresponding test method guidelines for the MIL-STD-461 D tests are provided in MIL-STD-462D. These test methods are well documented with the exception of the receiver antenna port susceptibility tests (intermodulation, cross modulation, and rejection of undesired signals) which must be tailored to the specific type of receiver that is being tested. Thus, test methods addressed in this guide consist only of antenna port tests designed to evaluate receiver susceptibility characteristics. MIL-STD-462D should be referred for guidance pertaining to test methods for EMI tests other than the antenna port tests. The scope of this test guide includes: (1) a discussion of generic DS receiver performance characteristics; (2) a summary of S-band TDRSS receiver operation; (3) a discussion of DS receiver EMI susceptibility mechanisms and characteristics; (4) a summary of military standard test guidelines; (5) recommended test approach and methods; and (6) general conclusions and recommendations for future studies in the area of spread spectrum receiver testing.

Wheeler, M. L.↗
NASA NTRS1998

Prediction Based Design of Fire Detection for Buildings with Ceiling Heights between 9m and 18m

The purpose of this paper is to provide the experimental and theoretical background necessary to extend guidelines to ceiling heights between 9 m and 18 m. Based on the results of experiments conducted in 15 m and 22 m high hangars, detector activation thresholds and detector spacing are analyzed for both smoke and heat detectors. Only ceiling mounted detection devices are analyzed in this paper. In addition to the detector threshold study, the predictive capabilities of computer fire model simulations were compared with experimental results. This comparison, which is based on 12 fire tests, resulted in the development of a new ceiling jet algorithm to model phenomena which had not been included in previous algorithms. The improved algorithm provides a better representation of the development of the ceiling jet temperature to a growing hot layer and a better estimation of plume centerline temperature. Guidelines are examined, based on the experimental results, for fire detector spacing, placement, and sensitivity. Recommendations concerning the use of computer fire models at these heights are made as a function of fire size and hot layer development. The role of draft curtains is discussed and their impact on detector activation is demonstrated.

Davis, W. D.↗
NASA NTRS1999

Simulation of Combustion Systems with Realistic g-Jitter

A number of facilities are available for microgravity combustion experiments: aircraft, drop tower, sounding rocket, space shuttle and, in the future, the international space station (ISS). Acceleration disturbances or g-jitter about the background level of reduced gravity exist in all the microgravity facilities. While g-jitter is routinely measured, a quantitative comparison of the quality of g-jitter among the different microgravity facilities has not been compiled. Low frequency g-jitter (< 1 Hz) has been repeatedly observed to disturb a number of combustion systems. Guidelines regarding tolerable levels of acceleration disturbances for a given combustion system have been developed for use in the design of ISS experiments. The validity of these guidelines, however, remains unknown. In this project, recently funded by NASA, a transient, fully three-dimensional simulation code will be developed to simulate the effects of realistic g-jitter on a number of combustion systems. Acceleration disturbances of realistic orientation, magnitude and time dependence will be included in the simulation. Since this is a newly funded project with code development just under-way no simulation results will be presented. Instead, first a short review of the relevant background concerning g-jitter will be given followed by a section on the proposed technical approach.

Mell, William E.↗
NASA NTRS1998

Factors Affecting Fiber Design and Selection for Advanced Ceramic Composites

Structural Ceramic Matrix Composites (CMC) have the potential for application in the hot sections of a variety of advanced propulsion and power systems. It is therefore necessary to have a general understanding of the key properties of CMC and Reinforcing Fibers. This need is complicated by the wide variety of application conditions and structural requirements for which CMC's will be used, and the proprietary concerns of the design engineers. CMC's, to be successful, must display properties which are competitive with the currently used high temperature structural materials: (i.e., Iron and Nickel based superalloys, tough monolithic ceramics, and carbon/carbon composites.) Structural CMC offers several areas of competition: (1) performance, (i.e., strength and strength retention, creep resistance, and thermal conductivity), (2) reliability (i.e., environmental durability, and damage tolerance) and (3) processing (i.e., capability for varying sizes and shapes, and cost effective fabrication). The presentation further discusses, and illustrates with fiber and CMC data the key fiber properties and processes which strongly affect each CMC area of competition. The presentation further discusses the current knowledge of the important factors which control the key fiber properties. A design guidelines for the optimum fiber characteristics is developed, and the currently available fibers are compared against those guidelines.

DiCarlo, James A.↗
NASA NTRS2000

Some Notes on Sparks and Ignition of Fuels

This report compliments a concurrent analysis of the electromagnetic field threat to the fuel system of a transport aircraft. The accompanying effort assessed currents, voltages and power levels that may be induced upon fuel tank wiring from radio transmitters (inside and outside the aircraft). In addition to this, it was also essential to determine how much voltage, current, or power is required to create a fuel-vapor ignition hazard. The widely accepted minimum guideline for aircraft fuel-vapor ignition is the application of a 0.2 millijoule energy level. However, when considering radio frequency (RF) sources, this guideline is seriously inadequate. This report endeavors to bridge the gap between a traditional understanding of electrical breakdown, heating and combustion; and supplement the knowledge with available information regarding aircraft fuel-vapor ignition by RF sources

Fisher, Franklin A.↗
NASA NTRS2000

Intelligent Tutoring Systems for Procedural Task Training of Remote Payload Operations at NASA

Intelligent Tutoring Systems (ITSs) encode and apply the subject matter and teaching expertise of experienced instructors to provide students with individualized instruction automatically. ITSs complement training simulators by providing automated instruction when it is not economical or feasible to dedicate an instructor to each student during training simulations. Despite their proven training effectiveness and favorable operating cost, however, relatively few ITSs are in use. This is largely because it is usually costly and difficult to encode the task knowledge used by the ITS to evaluate the student's actions and assess the student's performance. Procedural tasks are tasks for which there exist procedures, guidelines, and strategies that determine the correct set of steps to be taken within each situation. To lower the cost and difficulty of creating tutoring systems for procedural task training, Stottler Henke Associates, Inc. (SHAI) worked closely with the Operations Training Group at NASA's Marshall Space Flight Center to develop the Task Tutor Toolkit (T (exp 3)), a generic tutoring system shell and scenario authoring tool. The Task Tutor Toolkit employs a case-based reasoning approach where the instructor creates a procedure template that specifies the range of student actions that are "correct" within each scenario. Because each procedure template is specific to a single scenario, the system can employ relatively simple reasoning methods to represent a correct set of actions and assess student performance. This simplicity enables a non-programmer to specify task knowledge quickly and easily by via graphical user interface, using a "demonstrate, generalize, and annotate" paradigm, that recognizes the range of possible valid actions and infers principles understood (or misunderstood) by the student when those actions are carried out. The Task Tutor Toolkit was also designed to be modular and general, so that it can be interfaced with a wide range of training simulators and support a variety of training domains. SHAI and NASA applied the Task Tutor Toolkit to create the Remote Payload Operations Tutor (RPOT). RPOT is a specific tutoring system application which lets scientists who are new to space mission operations learn to monitor and control their experiments aboard the International Space Station according to NASA payload regulations, guidelines, and procedures. The RPOT simulator lets students practice these skills by monitoring the telemetry variable values of a simple, hypothetical experiment, sending commands to the experiment, coordinating with NASA personnel via voice communication loops, and submitting and retrieving information via documents and forms. At the end of each scenario, RPOT displays the principles correctly or incorrectly demonstrated by the student, along with explanations and background information. The effectiveness of RPOT and the Task Tutor Toolkit are currently under evaluation at NASA.

Ong, James↗
NASA NTRS2001

Simulation of Combustion Systems with Realistic g-Jitter

A number of facilities are available for microgravity combustion experiments: aircraft, drop towers, sounding rockets, the space shuttle, and, in the future, the International Space Station (ISS). Acceleration disturbances or g-jitter about the background level of reduced gravity exist in all these microgravity facilities. While g-jitter is routinely measured, a quantitative comparison of the quality of g-jitter among the different microgravity facilities, in terms of its affects on combustion experiments, has not been compiled. Low frequency g-jitter (< 1 Hz) has been repeatedly observed to disturb a number of combustion systems. Guidelines regarding tolerable levels of acceleration disturbances for combustion experiments have been developed for use in the design of ISS experiments. The validity of these guidelines, however, remains unknown. In this project a transient, 3-D numerical model is under development to simulate the effects of realistic g-jitter on a number of combustion systems. The measured acceleration vector or some representation of it can be used as input to the simulation.

Mell, W. E.↗
NASA NTRS2001

The Objectives of NASA's Living with a Star Space Environment Testbed

NASA is planning to fly a series of Space Environment Testbeds (SET) as part of the Living With A Star (LWS) Program. The goal of the testbeds is to improve and develop capabilities to mitigate and/or accommodate the affects of solar variability in spacecraft and avionics design and operation. This will be accomplished by performing technology validation in space to enable routine operations, characterize technology performance in space, and improve and develop models, guidelines and databases. The anticipated result of the LWS/SET program is improved spacecraft performance, design, and operation for survival of the radiation, spacecraft charging, meteoroid, orbital debris and thermosphere/ionosphere environments. The program calls for a series of NASA Research Announcements (NRAs) to be issued to solicit flight validation experiments, improvement in environment effects models and guidelines, and collateral environment measurements. The selected flight experiments may fly on the SET experiment carriers and flights of opportunity on other commercial and technology missions. This paper presents the status of the project so far, including a description of the types of experiments that are intended to fly on SET-1 and a description of the SET-1 carrier parameters.

Barth, Janet L.↗
NASA NTRS2001

Simple Thermal Environment Model (STEM) User's Guide

This report presents a Simple Thermal Environment Model (STEM) for determining appropriate engineering design values to specify the thermal environment of Earth-orbiting satellites. The thermal environment of a satellite, consists of three components: (1) direct solar radiation, (2) Earth-atmosphere reflected shortwave radiation, as characterized by Earth's albedo, and (3) Earth-atmosphere-emitted outgoing longwave radiation (OLR). This report, together with a companion "guidelines" report provides methodology and guidelines for selecting "design points" for thermal environment parameters for satellites and spacecraft systems. The methods and models reported here are outgrowths of Earth Radiation Budget Experiment (ERBE) satellite data analysis and thermal environment specifications discussed by Anderson and Smith (1994). In large part, this report is intended to update (and supersede) those results.

Justus, C.G.↗
NASA NTRS1995

Verification and Validation of Simulation Models for High-Speed Flow Fields

This paper is largely based on the paper titled "Guide to Credible Computational Fluid Dynamics Simulations (Invited)" (AIAA Paper 95-2225). The significance of computational fluid dynamics (CFD) simulations depends solely on their credibility. A customer of CFD products -- simulations and software -- expects that these products are credible for the intended use. Simulation model verification and validation are critical in establishing the credibility of simulations and in certifying simulation software. The only thing that matters in establishing the credibility is uncertainty, not veracity or validity. The sensitivity-uncertainty analysis is the key to the establishment of this credibility. Assessing the credibility of complex simulation results poses a significant challenge. Terminology, concepts, framework, and guidelines are presented for addressing this challenge. Verification assesses whether the problem is solved correctly and estimates the level of computational accuracy of simulations; validation determines whether the right problem is solved and assesses the level of validity of the simulation model by estimating the degree to which simulations accurately represent reality. These concepts and the related guidelines are discussed with examples from high-speed flow fields.

Mehta, Unmeel B.↗
NASA NTRS1995

Planetary Protection and Mars Exploration

Planetary spacecraft to explore Mars are subject to international and NASA policy regarding biological cleanliness. This policy is referred to as planetary protection and it establishes guidelines to prevent biological cross-contamination of planets during solar system exploration missions. Mars mission designs and exploration strategies are incomplete without consideration of planetary protection. In this paper, the foundation for planetary protection policy will be reviewed and key issues identified. Existing guidelines governing both forward and back contamination will be summarized. Various Mars exploration scenarios will be examined and the impact of planetary protection requirements will be assessed. Technical issues that need resolution will also be identified. Finally, there will be a discussion of anticipated public attitudes concerning the risk of back contamination from Mars sample return missions.

DeVincenzi, D. L.↗
NASA NTRS1997

Free Flight and Self-Separation from the Flight Deck Perspective

The concept of "free flight", while still being developed, is intended to emphasize more, flexibility for operators in the National Airspace System (NAS) by providing more separation responsibility to pilots, New technologies, procedures, and concepts have been suggested by the aviation community to enable this task; however, much work needs to be accomplished to help define and evaluate the concept feasibility. The purpose of this simulation was to begin examining some of the communication and procedural issues associated with self-separation in the enroute environment. A simulation demonstration was conducted in the Boeing 747-400 simulator at NASA Ames Research Center. Commercial pilots (from a U.S. domestic carrier) current on the B747-400 aircraft were the participants. Ten flight crews (10 captains, 10 first officers) flew in the Denver enroute airspace environment. A new alerting logic designed to allow for airborne self-separation was created for this demonstration. This logic assumes automatic dependent surveillance broadcast (ADS-B) capability and represented aircraft up to 120 nautical miles on the display. The new flight deck display features were designed and incorporated on the existing navigational display in the simulator to allow for increased traffic and maneuvering information to the flight crew. New tools were also provided to allow the crews to assess conflicts and potential maneuvers before implementing them. Each of the flight crews flew eight different scenarios in the Denver enroute airspace. The scenarios included eight to ten other aircraft, and each scenario was created with the intent of having one of the other aircraft become an operational conflict for our simulator aircraft. Different types of conflict geometries were represented across the eight scenarios. Also, some scenarios allowed for more time to detect a potential clearance, while others allowed for less time for'detection. Additionally, the crews were asked to a ply the Visual Flight Rules (VFR) right of way rules when determining who should maneuver in a conflict situation; therefore, the scenarios were designed to test different applications of those recommendations, Data analyses include an evaluation of crew procedures and communication. The application of the VFR right-of-way rules are being explored. Timing variables are being examined to determine potential efficiency differences between scenarios and conflict types. Proximity of aircraft will be assessed as one indication of the operational safety. The intent of these evaluations is to help provide definitions and guidelines of negotiation procedures in a self-separation environment assuming automated data link technology (ADS-B). Also, definitions of likely flight crew maneuvers and application to current VFR right-of-way rules may be obtained, along with guidelines for negotiation procedures between flight crews.

Lozito, Sandra↗
NASA NTRS2002

Search and Rescue Operations of Aircraft in Africa: Some Compelling Issues

The world aviation community has felt the compelling need for a well-coordinated global programme for search and rescue operations of aircraft ever since commercial aviation was regulated in 1944. Guidelines and plans of action for search and rescue have therefore been considered critical in the event of an aircraft accident. This fact is eminently brought to bear in the continental regions of Africa and South America in particular, where vast expanses of land are still uninhabited or sparsely populated and controlled flight into terrain (CFIT-where an aircraft may crash on land while still under the control of technical crew) is a common occurrence. There are numerous guidelines that have been adopted under the umbrella of the International Civil Aviation Organization which are already in place for the provision of search and rescue operations pertaining to aircraft. However, when an accident occurs in the territory of a State, there are sensitivities involving the State in which the aircraft concerned was registered and issues of sovereignty which have to be considered. Additionally. issues such as the voluntary nature of the search and rescue services offered. confidentiality, timeliness of such operations, fairness and uniformity all play a critical role. This article addresses the issue of search and rescue operations in Africa and examines in some detail where the world aviation community is right now and where it is headed in this important field of human endeavour.

Abeyratne, Ruwantissa I. R.↗
NASA NTRS2003

Best Practices for Reduction of Uncertainty in CFD Results

This paper describes a proposed best-practices system that will present expert knowledge in the use of CFD. The best-practices system will include specific guidelines to assist the user in problem definition, input preparation, grid generation, code selection, parameter specification, and results interpretation. The goal of the system is to assist all CFD users in obtaining high quality CFD solutions with reduced uncertainty and at lower cost for a wide range of flow problems. The best-practices system will be implemented as a software product which includes an expert system made up of knowledge databases of expert information with specific guidelines for individual codes and algorithms. The process of acquiring expert knowledge is discussed, and help from the CFD community is solicited. Benefits and challenges associated with this project are examined.

Mendenhall, Michael R.↗
NASA NTRS2004

Design and Experimental Verification of Deployable/Inflatable Ultra-Lightweight Structures

Because launch cost of a space structural system is often proportional to the launch volume and mass and there is no significant gravity in space, NASA's space exploration programs and various science missions have stimulated extensive use of ultra-lightweight deployable/inflatable structures. These structures are named here as Highly Flexible Structures (HFSs) because they are designed to undergo large displacements, rotations, and/or buckling without plastic deformation under normal operation conditions. Except recent applications to space structural systems, HFSs have been used in many mechanical systems, civil structures, aerospace vehicles, home appliances, and medical devices to satisfy space limitations, provide special mechanisms, and/or reduce structural weight. The extensive use of HFSs in today's structural engineering reveals the need of a design and analysis software and a database system with design guidelines for practicing engineers to perform computer-aided design and rapid prototyping of HFSs. Also to prepare engineering students for future structural engineering requires a new and easy-to- understand method of presenting the complex mathematics of the modeling and analysis of HFSs. However, because of the high flexibility of HFSs, many unique challenging problems in the modeling, design and analysis of HFSs need to be studied. The current state of research on HFSs needs advances in the following areas: (1) modeling of large rotations using appropriate strain measures, (2) modeling of cross-section warpings of structures, (3) how to account for both large rotations and cross- section warpings in 2D (two-dimensional) and 1D structural theories, (4) modeling of thickness thinning of membranes due to inflation pressure, pretension, and temperature change, (5) prediction of inflated shapes and wrinkles of inflatable structures, (6) development of efficient numerical methods for nonlinear static and dynamic analyses, and (7) filling the gap between geometrically exact elastic analysis and elastoplastic analysis. The objectives of this research project were: (1) to study the modeling, design, and analysis of deployable/inflatable ultra-lightweight structures, (2) to perform numerical and experimental studies on the static and dynamic characteristics and deployability of HFSs, (3) to derive guidelines for designing HFSs, (4) to develop a MATLAB toolbox for the design, analysis, and dynamic animation of HFSs, and (5) to perform experiments and establish an adequate database of post-buckling characteristics of HFSs.

Pai, P. Frank↗
NASA NTRS1990

New Directions in Space: A Report on the Lunar and Mars Initiatives

This report focuses on one aspect of the current space program: The establishment of a manned base on the Moon and the manned exploration of Mars. These missions were announced by the President last year as a major U.S. space policy objective to be implemented under the leadership of the Vice President, acting as Chairman of the National Space Council. On March 8, 1990, the White House released Presidential guidelines for the execution of the lunar and Mars programs. The guidelines stressed the need for new approaches and the development of innovative technologies with a potential for major cost, schedule and performance improvements. They also called for a competitive environment, with several years allotted to the definition of at least two significantly different human space exploration "reference architectures." Selection of the final technical concepts for the mission is scheduled to occur only after the relative merits of the competing reference architectures have been evaluated.

Seitz, Frederick↗
NASA NTRS1998

Results From Mars Show Electrostatic Charging of the Mars Pathfinder Sojourner Rover

Indirect evidence (dust accumulation) has been obtained indicating that the Mars Pathfinder rover, Sojourner, experienced electrostatic charging on Mars. Lander camera images of the Sojourner rover provide distinctive evidence of dust accumulation on rover wheels during traverses, turns, and crabbing maneuvers. The sol 22 (22nd Martian "day" after Pathfinder landed) end-of-day image clearly shows fine red dust concentrated around the wheel edges with additional accumulation in the wheel hubs. A sol 41 image of the rover near the rock "Wedge" (see the next image) shows a more uniform coating of dust on the wheel drive surfaces with accumulation in the hubs similar to that in the previous image. In the sol 41 image, note particularly the loss of black-white contrast on the Wheel Abrasion Experiment strips (center wheel). This loss of contrast was also seen when dust accumulated on test wheels in the laboratory. We believe that this accumulation occurred because the Martian surface dust consists of clay-sized particles, similar to those detected by Viking, which have become electrically charged. By adhering to the wheels, the charged dust carries a net nonzero charge to the rover, raising its electrical potential relative to its surroundings. Similar charging behavior was routinely observed in an experimental facility at the NASA Lewis Research Center, where a Sojourner wheel was driven in a simulated Martian surface environment. There, as the wheel moved and accumulated dust (see the following image), electrical potentials in excess of 100 V (relative to the chamber ground) were detected by a capacitively coupled electrostatic probe located 4 mm from the wheel surface. The measured wheel capacitance was approximately 80 picofarads (pF), and the calculated charge, 8 x 10(exp -9) coulombs (C). Voltage differences of 100 V and greater are believed sufficient to produce Paschen electrical discharge in the Martian atmosphere. With an accumulated net charge of 8 x 10(exp -9) C, and average arc time of 1 msec, arcs can also occur with estimated arc currents approaching 10 milliamperes (mA). Discharges of this magnitude could interfere with the operation of sensitive electrical or electronic elements and logic circuits. Sojourner rover wheel tested in laboratory before launch to Mars. Before launch, we believed that the dust would become triboelectrically charged as it was moved about and compacted by the rover wheels. In all cases observed in the laboratory, the test wheel charged positively, and the wheel tracks charged negatively. Dust samples removed from the laboratory wheel averaged a few ones to tens of micrometers in size (clay size). Coarser grains were left behind in the wheel track. On Mars, grain size estimates of 2 to 10 mm were derived for the Martian surface materials from the Viking Gas Exchange Experiment. These size estimates approximately match the laboratory samples. Our tentative conclusion for the Sojourner observations is that fine clay-sized particles acquired an electrostatic charge during rover traverses and adhered to the rover wheels, carrying electrical charge to the rover. Since the Sojourner rover carried no instruments to measure this mission's onboard electrical charge, confirmatory measurements from future rover missions on Mars are desirable so that the physical and electrical properties of the Martian surface dust can be characterized. Sojourner was protected by discharge points, and Faraday cages were placed around sensitive electronics. But larger systems than Sojourner are being contemplated for missions to the Martian surface in the foreseeable future. The design of such systems will require a detailed knowledge of how they will interact with their environment. Validated environmental interaction models and guidelines for the Martian surface must be developed so that design engineers can test new ideas prior to cutting hardware. These models and guidelines cannot be validated without actual flighata. Electrical charging of vehicles and, one day, astronauts moving across the Martian surface may have moderate to severe consequences if large potential differences develop. The observations from Sojourner point to just such a possibility. It is desirable to quantify these results. The various lander/rover missions being planned for the upcoming decade provide the means for doing so. They should, therefore, carry instruments that will not only measure vehicle charging but characterize all the natural and induced electrical phenomena occurring in the environment and assess their impact on future missions.

Kolecki, Joseph C.↗