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NASA NTRS1990

Plasma flow reversals at the dayside magnetopause and the origin of asymmetric polar cap convection

Events observed in a fast plasma experiment, where the y-component of the plasma flow within the low latitude boundary layer and magnetopause current layer was oppositely directed to that in the adjacent magnetosheath, are examined. The observations are shown to be qualitatively and quantitatively consistent with previous observations of accelerated flows at the magnetopause and with models of magnetic reconnection, with reconnection occurring at low latitudes near the GSE XY plane, independently of the magnitude or the sign of the y-component ot the local magnetosheath magnetic field. Local magnetic shears at the magnetopause for these events (in 60-180 deg range) and the fact that these events occur at low latitudes do not support the antiparallel merging hypothesis. The observations of B(y)-dependent flow reversals demonstrate how the asymmetric polar cap convection and related phenomena, such as the Svalgaard-Mansurov effect, originate in magnetic reconnection at the dayside magnetopause.

Gosling, J. T.↗

NASA NTRS1987

RICIS research

The principle focus of one of the RICIS (Research Institute for Computing and Information Systems) components is computer systems and software engineering in-the-large of the lifecycle of large, complex, distributed systems which: (1) evolve incrementally over a long time; (2) contain non-stop components; and (3) must simultaneously satisfy a prioritized balance of mission and safety critical requirements at run time. This focus is extremely important because of the contribution of the scaling direction problem to the current software crisis. The Computer Systems and Software Engineering (CSSE) component addresses the lifestyle issues of three environments: host, integration, and target.

Mckay, Charles W.↗

NASA NTRS1990

Software: Where we are and what is required in the future

The current status and future direction of flight critical software are presented in the form of view-graphs. The following subject areas are covered: the programmers environment; Saab Grippen Flight test program; present day tools; analysis tools (reverse engineering); automatic code generators; and future plans.

Cohen, Jerry↗

NASA NTRS1991

The 1991 Goddard Conference on Space Applications of Artificial Intelligence

The purpose of this annual conference is to provide a forum in which current research and development directed at space applications of artificial intelligence can be presented and discussed. The papers in this proceeding fall into the following areas: Planning and scheduling, fault monitoring/diagnosis/recovery, machine vision, robotics, system development, information management, knowledge acquisition and representation, distributed systems, tools, neural networks, and miscellaneous applications.

Rash, James L.↗

NASA NTRS1991

Certification of lightning protection for a full-authority digital engine control

FADEC systems present many challenges to the lightning protection engineer. Verification of the protection-design adequacy for certification purposes presents additional challenges. The basic requirements of the certification plan of a FADEC is to demonstrate compliance with Federal Airworthiness Regulations (FAR) 25.1309 and 25.581. These FARs are intended for transport aircraft, but there are equivalent sections for general aviation aircraft, normal and transport rotorcraft. Military aircraft may have additional requirements. The criteria for demonstration of adequate lightning protection for a FADEC systems include the procedures outlined in FAA Advisory Circular (AC) 20-136, Protection of aircraft electrical/electronic systems against the indirect effects of lightning. As FADEC systems, including the interconnecting wiring, are generally not susceptible to direct attachment of lightning currents, the verification of protection against indirect effects is primarily described.

Dargi, M.↗

NASA NTRS1990

Space Applications of Artificial Intelligence; 1990 Goddard Conference, Greenbelt, MD, May 1, 2, 1990, Selected Papers

The papers presented at the 1990 Goddard Conference on Space Applications of Artificial Intelligence are given. The purpose of this annual conference is to provide a forum in which current research and development directed at space applications of artificial intelligence can be presented and discussed. The proceedings fall into the following areas: Planning and Scheduling, Fault Monitoring/Diagnosis, Image Processing and Machine Vision, Robotics/Intelligent Control, Development Methodologies, Information Management, and Knowledge Acquisition.

Rash, James L.↗

NASA NTRS1992

The 1992 Goddard Conference on Space Applications of Artificial Intelligence

The purpose of this conference is to provide a forum in which current research and development directed at space applications of artificial intelligence can be presented and discussed. The papers fall into the following areas: planning and scheduling, control, fault monitoring/diagnosis and recovery, information management, tools, neural networks, and miscellaneous applications.

Rash, James L.↗

NASA NTRS1992

Space Exploration Initiative - Overview, current status, near term plans

An overview is presented of the Space Exploration Initiative (SEI) describing current activities, accomplishemnts, and directions. The program is considered in terms of activities relevant to the three phases which are: manned robotic/precursor missions, manned lunar missions, and manned Mars missions. SEI is shown to be in the First Lunar Outpost (FLO) mission phase which is based on an early manned lunar return, and development is described of earth-to-orbit (ETO) vehicles, a translunar injection stage, and a lunar surface habitat. Two ETO vehicles are considered, and the translunar injection stage is illustrated. The FLO mission is also considered as an initiation of the design activity for the Mars mission so that the requirements and preliminary designs could be defined. The FLO program demonstrates the feasibility of a manned return to the moon as an initiation of subsequent SEI activities.

Adams, Alan M.↗

NASA NTRS1993

Analog-To-Digital Converter For Sum-Of-Squares Measurements

Analog-to-digital converter (ADC) circuit designed as part of larger circuit intended to measure root-mean-square current on 20-kHz powerline. Provides digital output of 11 bits of data plus 1-bit overflow signal at sampling rate of 4 MHz. Output processed by multiplying-and-accumulating circuitry to obtain sum of squares and digitized current samples accumulated during preset number of consecutive sampling periods. Used to digitize current samples from ADC directly as alternative or auxiliary output. Notable features include low power and fast conversion.

Osborn, Stephen H.↗

NASA NTRS1992

Techniques for optimal crop selection in a controlled ecological life support system

A Controlled Ecological Life Support System (CELSS) utilizes a plant's natural ability to regenerate air and water while being grown as a food source in a closed life support system. Current plant research is directed toward obtaining quantitative empirical data on the regenerative ability of each species of plant and the system volume and power requirements. Two techniques were adapted to optimize crop species selection while at the same time minimizing the system volume and power requirements. Each allows the level of life support supplied by the plants to be selected, as well as other system parameters. The first technique uses decision analysis in the form of a spreadsheet. The second method, which is used as a comparison with and validation of the first, utilizes standard design optimization techniques. Simple models of plant processes are used in the development of these methods.

Mccormack, Ann↗

NASA NTRS1992

A prototype automatic phase compensation module

The growing demands for high gain and accurate satellite communication systems will necessitate the utilization of large reflector systems. One area of concern of reflector based satellite communication is large scale surface deformations due to thermal effects. These distortions, when present, can degrade the performance of the reflector system appreciable. This performance degradation is manifested by a decrease in peak gain, and increase in sidelobe level, and pointing errors. It is essential to compensate for these distortion effects and to maintain the required system performance in the operating space environment. For this reason the development of a technique to offset the degradation effects is highly desirable. Currently, most research is direct at developing better material for the reflector. These materials have a lower coefficient of linear expansion thereby reducing the surface errors. Alternatively, one can minimize the distortion effects of these large scale errors by adaptive phased array compensation. Adaptive phased array techniques have been studied extensively at NASA and elsewhere. Presented in this paper is a prototype automatic phase compensation module designed and built at NASA Lewis Research Center which is the first stage of development for an adaptive array compensation module.

Terry, John D.↗

NASA NTRS1991

On-orbit demonstrations of automated closure and capture using ESA-developed proximity operations technologies and an existing serviceable NASA Explorer platform spacecraft

Since 1984 the European Space Agency (ESA) has been working to develop an autonomous rendezvous and docking capability to enable Hermes to dock automatically with Columbus. As a result, ESA (with Matra, MBB, and other space companies) have developed technologies that are directly supportive of the current NASA initiative for Automated Rendezvous and Capture. Fairchild and Matra would like to discuss the results of the applicable ESA/Matra rendezvous and capture developments and suggest how these capabilities could be used together with an existing NASA Explorer Platform satellite to minimize new development and accomplish a cost-effective automatic closure and capture demonstration program.

Hohweisner, Bill↗

NASA NTRS1991

On-orbit demonstration of automated closure and capture using ESA-developed proximity operations technologies and an existing, serviceable NASA Explorer Platform spacecraft

The European Space Agency (ESA) has been working to develop an autonomous rendezvous and docking capability since 1984 to enable Hermes to automatically dock with Columbus. As a result, ESA with Matra, MBB, and other space companies have developed technologies that are also directly supportive of the current NASA initiative for Automated Rendezvous and Capture. Fairchild and Matra would like to discuss the results of the applicable ESA/Matra rendezvous and capture developments, and suggest how these capabilities could be used, together with an existing NASA Explorer Platform satellite, to minimize new development and accomplish a cost effective automatic closure and capture demonstration program. Several RV sensors have been developed at breadboard level for the Hermes/Columbus program by Matra, MBB, and SAAB. Detailed algorithms for automatic rendezvous, closure, and capture have been developed by ESA and CNES for application with Hermes to Columbus rendezvous and docking, and they currently are being verified with closed-loop software simulation. The algorithms have multiple closed-loop control modes and phases starting at long range using GPS navigation. Differential navigation is used for coast/continuous thrust homing, holdpoint acquisition, V-bar hopping, and station point acquisition. The proximity operation sensor is used for final closure and capture. A subset of these algorithms, comprising the proximity operations algorithms, could easily be extracted and tailored to a limited objective closure and capture flight demonstration.

Hohwiesner, Bill↗

NASA NTRS1992

Modelling a single phase voltage controlled rectifier using Laplace transforms

The development of a 20 kHz, AC power system by NASA for large space projects has spurred a need to develop models for the equipment which will be used on these single phase systems. To date, models for the AC source (i.e., inverters) have been developed. It is the intent of this paper to develop a method to model the single phase voltage controlled rectifiers which will be attached to the AC power grid as an interface for connected loads. A modified version of EPRI's HARMFLO program is used as the shell for these models. The results obtained from the model developed in this paper are quite adequate for the analysis of problems such as voltage resonance. The unique technique presented in this paper uses the Laplace transforms to determine the harmonic content of the load current of the rectifier rather than a curve fitting technique. Laplace transforms yield the coefficient of the differential equations which model the line current to the rectifier directly.

Kraft, L. Alan↗

NASA NTRS1993

The 1993 Goddard Conference on Space Applications of Artificial Intelligence

This publication comprises the papers presented at the 1993 Goddard Conference on Space Applications of Artificial Intelligence held at the NASA/Goddard Space Flight Center, Greenbelt, MD on May 10-13, 1993. The purpose of this annual conference is to provide a forum in which current research and development directed at space applications of artificial intelligence can be presented and discussed.

Hostetter, Carl F.↗

NASA NTRS1993

Modulation and coding for throughput-efficient optical free-space links

Optical direct-detection systems are currently being considered for some high-speed inter-satellite links, where data-rates of a few hundred megabits per second are evisioned under power and pulsewidth constraints. In this paper we investigate the capacity, cutoff-rate and error-probability performance of uncoded and trellis-coded systems for various modulation schemes and under various throughput and power constraints. Modulation schemes considered are on-off keying (OOK), pulse-position modulation (PPM), overlapping PPM (OPPM) and multi-pulse (combinatorial) PPM (MPPM).

Georghiades, Costas N.↗

NASA NTRS1993

Strategies and methodologies to develop techniques for computer-assisted analysis of gas phase formation during altitude decompression

It would be of operational significance if one possessed a device that would indicate the presence of gas phase formation in the body during hypobaric decompression. Automated analysis of Doppler gas bubble signals has been attempted for 2 decades but with generally unfavorable results, except with surgically implanted transducers. Recently, efforts have intensified with the introduction of low-cost computer programs. Current NASA work is directed towards the development of a computer-assisted method specifically targeted to EVA, and we are most interested in Spencer Grade 4. We note that Spencer Doppler Grades 1 to 3 have increased in the FFT sonogram and spectrogram in the amplitude domain, and the frequency domain is sometimes increased over that created by the normal blood flow envelope. The amplitude perturbations are of very short duration, in both systole and diastole and at random temporal positions. Grade 4 is characteristic in the amplitude domain but with modest increases in the FFT sonogram and spectral frequency power from 2K to 4K over all of the cardiac cycle. Heart valve motion appears to characteristic display signals: (1) the demodulated Doppler signal amplitude is considerably above the Doppler-shifted blow flow signal (even Grade 4); and (2) demodulated Doppler frequency shifts are considerably greater (often several kHz) than the upper edge of the blood flow envelope. Knowledge of these facts will aid in the construction of a real-time, computer-assisted discriminator to eliminate cardiac motion artifacts. There could also exist perturbations in the following: (1) modifications of the pattern of blood flow in accordance with Poiseuille's Law, (2) flow changes with a change in the Reynolds number, (3) an increase in the pulsatility index, and/or (4) diminished diastolic flow or 'runoff.' Doppler ultrasound devices have been constructed with a three-transducer array and a pulsed frequency generator.

Powell, Michael R.↗

NASA NTRS1993

Miniaturization in x ray and gamma ray spectroscopy

The paper presents advances in two new sensor technologies and a miniaturized associated electronics technology which, when combined, can allow for very significant miniaturization and for the reduction of weight and power consumption in x-ray and gamma-ray spectroscopy systems: (1) Mercuric iodide (HgI2) x-ray technology, which allows for the first time the construction of truly portable, high-energy resolution, non-cryogenic x-ray fluorescence (XRF) elemental analyzer systems, with parameters approaching those of laboratory quality cryogenic instruments; (2) the silicon avalanche photodiode (APD), which is a solid-state light sensitive device with internal amplification, capable of uniquely replacing the vacuum photomultiplier tube in scintillation gamma-ray spectrometer applications, and offering substantial improvements in size, ruggedness, low power operation and energy resolution; and (3) miniaturized (hybridized) low noise, low power amplification and processing electronics, which take full advantage of the favorable properties of these new sensors and allow for the design and fabrication of advanced, highly miniaturized x-ray and gamma-ray spectroscopy systems. The paper also presents experimental results and examples of spectrometric systems currently under construction. The directions for future developments are discussed.

Iwanczyk, Jan S.↗