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At least 487 records · Page 27

All sources NASA NTRS DOE OSTI

NASA NTRS1981

Charging and discharging characteristics of a rigid solar array

Two rigid solar array panels were subjected to a simulated geosynchronous orbit substorm environment. During the charging sequence, distributions of accumulated surface charge were measured under eclipse and sunlight conditions. Discharge events were characterized with respect to voltage pulse signatures and amplitudes on the solar array bus leads. Post-exposure analysis of the solar array panels indicated that the electrical characteristics were not degraded in spite of the substantial discharge actvity. However, significant cratering and discoloration of the Tedlar dielectric were observed.

Brady, G. F., Jr.↗

NASA NTRS1981

The recovery of the HEAO-2 observatory

In August 1980, the Second High Energy Astronomy Observatory suffered the simultaneous double failure of two gyros, leaving the observatory with one gyro less than what is required for operation. The function of the missing gyro was replaced to allow restoration of spacecraft operation by reprogramming the on-board computer to derive rate from star and sun sensors, and by utilizing complex procedures. Large sun sensor quantization, jump characteristics of the star tracker, and extremely limited computer memory capacity further complicated the problem. Recovery attempts continued for over three months, during which time a suitable rate algorithm was derived. Final verification of the technique was never completed, however, due to the unexpected revival of one of the failed gyros.

Rose, R. E.↗

NASA NTRS1982

Pulsed plasma thruster ignitor plug ignition characteristics

The operating characteristics of the semiconductor spark gap ignitor plug used to initiate the discharge in a pulsed plasma thruster are investigated. Current and voltage waveform measurements for the ignitor plug alone, and for the plug mounted in the thruster cathode indicate an average dynamic impedance of 0.2 ohms for a wide range of operating conditions, and a trigger circuit energy transfer efficiency to the plug on the order of 25%. Two modes of trigger ignition are found which are related to the rise time of the applied voltage pulse. Analysis of plasma characteristics reveals plug erosion to occur primarily in the semiconductor and anode regions, by mechanisms including plug metal embrittlement, plasma sputtering and vaporization caused by the discharge current pulse. Measurements also indicate a plume velocity on the order of 1580,000 cm/sec which increases with trigger circuit stored energy. The results establish levels of performance for future applications of semiconductor spark gap ignitor plugs in plasma devices.

Brady, M. E.↗

NASA NTRS1981

Behavioral and biological interactions with confined microsocieties in a programmed environment

This paper presents a summary of the background, objectives, and methodological approach of an ongoing research project devoted to the analysis of individual and small group performance effectiveness under conditions of isolation and confinement during extended residences in a continuously programmed environment. A more detailed description is provided of the results of a recent series of experiments designed and conducted to assess hormonal and behavioral effects of a change in group membership and size.

Emurian, H. H.↗

NASA NTRS1982

Behavioral and biological interactions with small groups in confined microsocieties

Requirements for high levels of human performance in the unfamiliar and stressful environments associated with space missions necessitate the development of research-based technological procedures for maximizing the probability of effective functioning at all levels of personnel participation. Where the successful accomplishment of such missions requires the coordinated contributions of several individuals collectively identified with the achievement of a common objective, the conditions for characterizing a team, crew, or functional group are operationally defined. For the most part, studies of group performances under operational conditions which emphasize relatively long exposure to extended mission environments have been limited by the constraints imposed on experimental manipulations to identify critical effectiveness factors. On the other hand, laboratory studies involving relatively brief exposures to contrived task situations have been considered of questionable generality to operational settings requiring realistic group objectives.

Brady, J. V.↗

NASA NTRS1983

A mathematical model for the doubly fed wound rotor generator

A mathematical analysis of a doubly-fed wound rotor machine used as a constant frequency generator is presented. The purpose of this analysis is to derive a consistent set of circuit equations which produce constant stator frequency and constant stator voltage. Starting with instantaneous circuit equations, the necessary rotor voltages and currents are derived. The model, thus obtained, is assumed to be valid, since the resulting relationships between mechanical power and active volt-amperes agrees with the results of others. In addition, the model allows for a new interpretation of the power flow in the doubly-fed generator.

Brady, F. J.↗

NASA NTRS1983

Noise characterization and minimization of a precision gyroscopic rate sensor

A program has been conducted to evaluate the noise signature of Space Telescope gyros. The Space Telescope gyros provide a three-axis attitude reference using six single-degree-of-freedom gyroscopes operated with pulse rebalance electronics; the rate sensor attitude quantization is 0.00025 arcsec. The results of the noise evaluation program, including error source characterization and identification of candidate design modifications, are summarized together with the results of prototype hardware testing. It is shown that the proposed design modifications can significantly improve the rate sensor noise performance.

Dougherty, H.↗

NASA NTRS1983

Pulsed plasma thruster ignitor plug ignition characteristics

Previously cited in issue 15, p. 2361, Accession no. A82-31913

Brady, M. E.↗

NASA NTRS1985

Trajectory Analysis and the Orbit Determination

Two programs aid in trajectory analysis. DPTRAJ, ODP and their supporting utility programs capable of handling massive amounts of data and performing numerical calculations required for solving navigation problems associated with planetary fly-by and lander missions. Used extensively in support of Voyager.

Alderson, D. J.↗

NASA NTRS1984

A mathematical model for the doubly-fed wound rotor generator, part 2

A mathematical analysis of a doubly-fed wound rotor generator is presented. The constraints of constant stator voltage and frequency to the circuit equations were applied and expressions for the currents and voltages in the machine obtained. The derived variables are redefined as direct and quadrature components. In addition, the apparent (complex) power for both the rotor and the stator are derived in terms of these redefined components.

Brady, F. J.↗

NASA NTRS1985

Description and test results of a variable speed, constant frequency generating system

The variable-speed, constant frequency generating system developed for the Mod-0 wind turbine is presented. This report describes the system as it existed at the conclusion of the project. The cycloconverter control circuit is described including the addition of field-oriented control. The laboratory test and actual wind turbine test results are included.

Brady, F. J.↗

NASA NTRS1986

A mathematical model for the doubly-fed wound rotor generator. II

Brady, F. J.↗

NASA NTRS1987

Kinematics at the intersection of the Garlock and Death Valley fault zones, California: Integration of TM data and field studies

The Garlock and Death Valley fault zones in SE California are two active strike-slip faults coming together on the east side of the Avawatz Mtns. The kinematics of this intersection, and the possible continuation of either fault zone, are being investigated using a combination of field mapping, and processing and interpretation of remotely sensed image data. Regional and local relationships are derivable from Thematic Mapper data (30 m resolution), including discrimination and relative age dating of alluvial fans, bedrock mapping, and fault mapping. Aircraft data provide higher spatial resolution over more limited areas. Hypotheses being considered are: (1) the Garlock fault extends east of the intersection; (2) the Garlock fault terminates at the intersection and the Death Valley fault continues southeastward; and (3) the Garlock fault has been offset right laterally by the Death Valley fault which continues to the southeast. Preliminary work indicates that the first hypothesis is invalid. From kinematic considerations, image analysis, and field work the third hypothesis is favored. The projected continuation of the Death Valley zone defines the boundary between the Mojave crustal block and the Basin and Range block.

Abrams, Michael↗

NASA NTRS1986

Behavioral and biological interactions with small groups in confined microsocieties

Research on small group performance in confined microsocieties was focused upon the development of principles and procedures relevant to the selection and training of space mission personnel, upon the investigation of behavioral programming, preventive monitoring and corrective procedures to enhance space mission performance effectiveness, and upon the evaluation of behavioral and physiological countermeasures to the potentially disruptive effects of unfamiliar and stressful environments. An experimental microsociety environment was designed and developed for continuous residence of human volunteers over extended time periods. Studies were then undertaken to analyze experimentally: (1) conditions that sustain group cohesion and productivity and that prevent social fragmentation and performance deterioration, (2) motivational effects performance requirements, and (3) behavioral and physiological effects resulting from changes in group size and composition. The results show that both individual and group productivity can be enhanced under such conditions by the direct application of contingency management principles to designated high-value tasks. Similarly, group cohesiveness can be promoted and individual social isolation and/or alienation prevented by the application of contingency management principles to social interaction segments of the program.

Brady, Joseph V.↗

NASA NTRS1986

An evaluation of candidate oxidation resistant materials for space applications in LEO

Ground based testing of materials considered for polyimide (Kapton) solar array blanket protection and graphite-epoxy stroctural member protection was performed in an RF plasma asher. Protective coatings on Kapton from various commercial sources and from NASA Lewis Research Center were exposed to the air plasma; and mass loss per unit area was measured for each sample. All samples evaluated provided some protection to the underlying surface, but metal-oxide-fluoropolymer coatings provided the best protection by exhibiting very little degradation after 47 hr of asher exposure. Mica paint was evaluated as a protective coating for graphite-epoxy structural members. Mica appeared to be resistant to attack by atomic oxygen, but only offered limited protection as a paint. this is believed to be due to the paint vehicle ashing underneath the mica leaving unattached mica flakes lying on the surface. The protective coatings on Kapton evaluated so far are promising but further research on protection of graphite-epoxy support structures is needed.

Rutledge, Sharon↗

NASA NTRS1987

High temperature radiator materials for applications in the low Earth orbital environment

Radiators must be constructed of materials which have high emittance in order to efficiently radiate heat from high temperature space power systems. In addition, if these radiators are to be used for applications in the low Earth orbital environment, they must not be detrimentally affected by exposure to atomic oxygen. Four materials selected as candidate radiator materials (304 stainless steel, copper, titanium-6% aluminum-4% vanadium (Ti-6%Al-4%V), and niobium-1% zirconium (Nb-1%Zr)) were surface modified by acid etching, heat treating, abrading, sputter texturing, electrochemical etching, and combinations of the above in order to improve their emittance. Combination treatment techniques with heat treating as the second treatment provided about a factor of two improvement in emittance for 304 stainless steel, Ti-6%Al-4%V, and Nb-1%Zr. A factor of three improvement in emittance occurred for discharge chamber sputter textured copper. Exposure to atomic oxygen in an RF plasma asher did not significantly change the emittance of those samples that had been heat treated as part of their texturing process. An evaluation of oxygen penetration is needed to understand how oxidation affects the mechanical properties of these materials when heat treated.

Rutledge, Sharon K.↗

NASA NTRS1988

Variable-Speed, Constant-Frequency Generation Of Power

Feedback of stator power and reactive volt-amperes determines rotor excitation. New method involves control circuit separating rotor excitation into generation of slip frequency and control of amplitude and phase. In control circuit, speed determines slip frequency, while stator power and reactive volt-amperes determine amplitude and phase of rotor current.

Brady, Frank J.↗

NASA NTRS1987

Expert systems relations in space applications

The problem of expert systems relations as they pertain to space applications is discussed. First, these systems are categorized and the relationships between them are analyzed. Then, the expert systems cooperation paradigm is proposed. This paradigm addresses various types of communication and coordination issues in an attempt to create a general model applicable in a number of situations.

Brady, Michael↗