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At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Triple mode Cepheid masses

Unconventional composition structures are proposed to explain the periods of the triple mode Cepheid aC And. A strong Cepheid wind appears to enrich helium in the convection zones down to about 60,000 K or 70,000 K. Then some downward partial mixing occurs to the bottom of a layer with about 1-q = .0005 of the stellar mass. It was found that AC And was not unlike anomalous Cepheids. However, masses of betwen one and two solar masses are suggested and the population is more likely a type two.

King, D. S.↗
NASA NTRS1980

Study of power management technology for orbital multi-100KWe applications. Volume 2: Study results

The preliminary requirements and technology advances required for cost effective space power management systems for multi-100 kilowatt requirements were identified. System requirements were defined by establishing a baseline space platform in the 250 KE KWe range and examining typical user loads and interfaces. The most critical design parameters identified for detailed analysis include: increased distribution voltages and space plasma losses, the choice between ac and dc distribution systems, shuttle servicing effects on reliability, life cycle costs, and frequency impacts to power management system and payload systems for AC transmission. The first choice for a power management system for this kind of application and size range is a hybrid ac/dc combination with the following major features: modular design and construction-sized minimum weight/life cycle cost; high voltage transmission (100 Vac RMS); medium voltage array or = 440 Vdc); resonant inversion; transformer rotary joint; high frequency power transmission line or = 20 KHz); energy storage on array side or rotary joint; fully redundant; and 10 year life with minimal replacement and repair.

Mildice, J. W.↗
NASA NTRS1980

Study of power management technology for orbital multi-100KWe applications. Volume 3: Requirements

Mid to late 1980's power management technology needs to support development of a general purpose space platform, capable of suplying 100 to 250 KWe to a variety of users in low Earth orbit are examined. A typical, shuttle assembled and supplied space platform is illustred, along with a group of payloads which might reasonably be expected to use such a facility. Examination of platform and user power needs yields a set of power requirements used to evaluate power management options for life cycle cost effectivness. The most cost effective ac/dc and dc systems are evaluated, specifically to develop system details which lead to technology goals, including: array and transmission voltages, best frequency for ac power transmission, and advantages and disadvantages of ac and dc systems for this application. System and component requirements are compared with the state-of-the-art to identify areas where technological development is required.

Mildice, J. W.↗
NASA NTRS1980

Effects of hirudin-induced activation of nonenzymatic fibrinolysis during immobilization stress

The specific inhibitor of thrombin, hirudin, was used for studying the mechanism of the activating effect of ACTH and adrenalin on nonenzymatic fibrinolytic activity (NEFA), the latter characterizing the function of the anticoagulation system (ACS). Simultaneous administration of ACTH and hirudin to animals subjected to immobilization stress did not reduce the effect of ACTH on NEFA, while simultaneous administration of adrenalin and hirudin revealed a diminished effect of the former. This suggests different mechanisms of ACTH and adrenalin effects upon NEFA: the stimulating effect of norepinephrine is realized through throminogenesis followed by activation of the ACS function and by increased NEFA and therefore inhibitable by hirudin which forms an inactive complex with thrombin. In fact the stimulating effect of ACTH upon NEFA is brought about specifically by another route than thrombinogenesis and thus occurs in the presence of hirudin. Hirudin itself has no effect upon NEFA.

Shapiro, F. B.↗
NASA NTRS1980

Power management for multi-100 KWe space systems

This paper examines mid to late 1980s power management technology needs to support development of a general-purpose space platform, capable of supplying 100 to 250 KWe to a variety of users in LEO. To that end, a typical Shuttle-assembled and supplied space platform is described, along with a group of payloads which might reasonably be expected to use such a facility. Examination of platform and user power needs yields a set of power system requirements used to evaluate power management options for life cycle cost effectiveness. The most cost-effective AC/DC and DC systems are evaluated, specifically to develop system details which lead to technology goals including array and transmission voltage, best frequency for AC power transmission, and advantages and disadvantages of AC and DC systems for this application. Finally, system and component requirements are compared with the state of the art to identify areas where technology development is required.

Mildice, J. W.↗
NASA NTRS1980

Application of a microprocessor to a spacecraft attitude control

The attitude control system (ACS) microprocessor development work spanned three main design areas: hardware and instruction set, ACS firmware, and hardware firmware verification testing. The processor hardware utilizes two parallel 4 bit microprocessors. The firmware includes data processing for five sensors, four attitude control laws, and telemetry and commands.

Brady, D. H.↗
NASA NTRS1980

Redundant operation of counter modules

A technique for the redundant operation of counter modules is described. Redundant operation is maintained by detecting the zero state of each counter and clearing the other to that state, thus periodically resynchronizing the counters, and obtaining an output from both counters through AC coupled diode-OR gates. Redundant operation of counter flip flops is maintained in a similar manner, and synchronous operation of redundant squarewave clock generators of the feedback type is effected by connecting together the feedback inputs of the squarewave generators through a coupling resistor, and obtaining an output from both generators through AC coupled diode-OR gates.

Nagano, S.↗
NASA NTRS1981

Flight performance of SEASAT-1 attitude control system

The paper describes the attitude control flight performance of SEASAT-A, (launched in June 1978), until failure of the power subsystem terminated the mission in Oct. 1978. Information provided by the satellite pertained to surface winds and coastal storm activity, currents and wave heights, ocean topography and temperature. The ACS used three-axis momentum exchange and magnetic momentum containment and was set in a nose-down configuration. Attitude control sensing was via horizon sensors and attitude anomalies, resulting from solar interference with the sensors, is covered in detail. Remedial action was taken by reconfiguring the IR scanners, but failure resulted nevertheless. Recommendations for similar future missions include consideration of the effect of light sources and circuit time constants and scan rates. A block diagram of the ACS is included.

Beach, S. W.↗
NASA NTRS1981

The plasma wave and quasi-static electric field instrument /PWI/ for dynamics Explorer-A

It is explained that the Plasma Wave Instrument (PWI) on Dynamics Explorer-A measures both plasma wave phenomena and quasi-static electric fields. The quasi-static electric fields are measured parallel to the spin axis of the spacecraft in a range of 2 mV/m to 2 V/m and perpendicular to the spin axis 0.5 mV/m to 2 V/m at 16 samples/s. The ac electric field sensors include a 200-m tip-to-tip long wire antenna and a 0.6-m short electric antenna, both of which are perpendicular to the spin axis, and a 9-m tip-to-tip tubular antenna parallel to the spin axis. AC electric wave fields are measured over a frequency range of 1 Hz to 2 MHz and over an amplitude range of 0.03 microvolt/m to 100 mV/m.

Shawhan, S. D.↗
NASA NTRS1982

Containerless processing technologies at the Jet Propulsion Laboratory

Acoustic and electrostatic levitation (EL) techniques for maintaining sample-wall distance in order to ensure contamination-free conditions during microgravity materials science experiments on board the Shuttle are examined. A laboratory model for acoustic containerless (AC) processing is described, noting the use of three commercially available drivers for sample levitation. The arrangement of the speakers results in a point node to which a liquid drop sample migrates. Varying the field through manipulation of the dB levels and phase of the drivers' outputs permits control of sample position and movement. Rotation of a styrofoam ball at 2000 rpm has been achieved. Oscillations can also be induced. An advanced version of the AC system is analytically defined, with further studies mentioned for stable levitation modes using a cylindrical chamber and optimizing acoustic power transfer between hot and cold regions. A tetrahedral EL system has proven to work in a reduced gravity environment. El involves imparting an electrical charge to an object and then positioning and maintaining it through use of EM fields. The presence of human operators to perform the processing on the Shuttle is mentioned as offering real-time capability of altering the experimental conditions.

Wang, T. G.↗
NASA NTRS1982

Development of the design concepts for a medium-scale wind tunnel magnetic suspension system

The magnitude of AC losses from a superconducting coil strongly indicates that the predicted scaling lawa are valid. The stainless steel bands around the test coil were the source of additional helium boiloff due to a transformer action and, hence, caused erroneously high AC loss measurements in the first run. However, removal of these bands for the second run produced data which are consistent with previous results on small scale multifilamentary superconducting coils.

Humphris, R. R.↗
NASA NTRS1984

Test bed ion engine development

A test bed ion (TBI) engine was developed to serve as a tool in exploring the limits of electrostatic ion thruster performance. A description of three key ion engine components, the decoupled extraction and amplified current (DE-AC) accelerator system, field enhanced refractory metal (FERM) hollow cathode and divergent line cusp (DLC) discharge chamber, whose designs and operating philosophies differ markedly from conventional thruster technology is given. Significant program achievements were: (1) high current density DE-AC accelerator system operation at low electric field stress with indicated feasibility of a 60 mA/sq cm argon ion beam; (2) reliable FERM cathode start up times of 1 to 2 secs. and demonstrated 35 ampere emission levels; (3) DLC discharge chamber plasma potentials negative of anode potential; and (4) identification of an efficient high plasma density engine operating mode. Using the performance projections of this program and reasonable estimates of other parameter values, a 1.0 Newton thrust ion engine is identified as a realizable technology goal. Calculations show that such an engine, comparable in beam area to a J series 30 cm thruster, could, operating on Xe or Hg, have thruster efficiencies as high as 0.76 and 0.78 respectively, with a 100 eV/ion discharge loss.

Aston, G.↗
NASA NTRS1984

Magnetic suspension and balance system study

A compact design for a superconducting magnetic suspension and balance system is developed for a 8 ft. x 8 ft. transonic wind tunnel. The main features of the design are: a compact superconducting solenoid in the suspended airplane model; permanent magnet wings; one common liquid helium dewar for all superconducting coils; efficient new race track coils for roll torques; use of established 11 kA cryostable AC conductor; acceptable AC losses during 10 Hz control even with all steel structure; and a 560 liter/hour helium liquefier. Considerable design simplicity, reduced magnet weights, and reduced heat leak results from using one common dewar which eliminates most heavy steel structure between coils and the suspended model. Operational availability is thought to approach 100% for such magnet systems. The weight and cost of the magnet system is approximately one-third that of previous less compact designs.

Boom, R. W.↗
NASA NTRS1983

Grounding and fault protection of the SMUD PVI array

If large terrestrial photovoltaic (PV) power plants are to provide an economic source of generation, low-cost, reliable and easily maintainable systems must be developed. In addition, if the system is to be a central station powerplant owned and operated by an electric utility, the design must also be consistent with utility specifications and design standards. The particular solutions developed to address these issues, with regard to grounding and fault protection, for the first phase of the Sacramento Municipal Utility District's (SMUD) 100 mw(ac) PV powerplant are presented. This plant, known as PV1, is nominally rated at 1 mw(ac) and is scheduled to be in operation by the spring of 1984.

Rosen, D.↗
NASA NTRS1984

High-resolution spectra of isotopic methanes near 1645 nm

It is demonstrated that the coincidence between Er:YAG laser emission and CH4 absorption is associated with the R(8) multiplet of C-13H4 instead of the R(6) of C-12H4. The Er:YAG emission was characterized as a laser emission at 6079.4/cm with a bandwidh of 2.2/cm and overlapping CH4 emission at 6078.7/cm. The R(6) component of C-12H4 closest to 6078.7/cm is calculated to be 6077.06/cm, corresponding to an absorption coefficient (AC) of 1.12/cm per atm. The F2-prime component of R(8) of C-13H4 has an AC of 0.308/cm per atm, which corresponds well with a range of 1.2-30.30/cm per atm based on a partial pressure of 1.6/89 ppm. The Er:YAG laser is a candidate for use in spectroscopic studies of CH4 atmospheric pollutants, natural gas movement and storage and gas accumulation in coal mines.

Fox, K.↗
NASA NTRS1985

Fast-Recovery, High-Voltage Power Diode

New family of fast-recovery high-voltage power diodes compatible with D60T and D7ST transistors developed. Have wide range of applications in spacecraft and aircraft electrical distribution equipment, dc/dc inverters, and ac motor controllers for high-horsepower electric motors operating from 480-volt ac lines. Fast-Recovery 1,200-V Power Diodes use chip of hexagonal geometry to maximize effective silicon area.

Sundberg, G.↗
NASA NTRS1985

Optical properties of hydrogenated amorphous carbon films grown from methane plasma

A 30 kHz ac glow discharge formed from methane gas was used to grow carbon films on InP substrates. Both the growth rate, and the realitive Ar ion sputtering rate at 3 keV varied monotonically with deposition power. Results from the N-15 nuclear reaction profile experiments indicated a slight drop in the hydrogen concentration as more energy was dissipated in the ac discharge. Values for the index of refraction and extinction coefficient ranged from 1.721 to 1.910 and 0 to -0.188, respectively. Optical bandgaps as high as 2.34 eV were determined.

Pouch, J. J.↗