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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

The effect of minority carrier mobility variations on the performance of high voltage silicon solar cells

A multistep diffusion processing schedule is described which allows the attainment of high open circuit voltages in 0.1 ohm/cm silicon cells. The schedule consists of a deep primary diffusion, followed by an acid etch of emmitter surface which is then followed by a shallow secondary diffusion. A correlation is made between the observed voltage increases and the time of primary diffusion. Results indicate that as the primary diffusion time increases, the voltage rises monotonically.

Weizer, V. G.↗
NASA NTRS1990

High-voltage picosecond photoconductor switch based on low-temperature-grown GaAs

A GaAs material grown by molecular beam epitaxy at a low substrate temperature was used to fabricate a photoconductor switch that produces 6-V picosecond electrical pulses. The pulses were produced on a microwave coplanar-strip transmission line lithographically patterned on the low-temperature (LT) GaAs. A 150-fs laser pulse was used to generate carriers in the LT GaAs gap between the metal strips, partially shorting a high DC voltage placed across the lines. The 6-V magnitude of the electrical pulses obtained is believed to be limited by the laser pulse power and not by the properties of the LT GaAs. Experiments were also performed on a picosecond photoconductor switch fabricated on a conventional ion-damaged silicon-on-sapphire substrate. Although comparable pulse durations were obtained, the highest pulse voltage achieved with the latter device was 0.6 V.

Frankel, Michael Y.↗
NASA NTRS1981

Multijunction high voltage concentrator solar cells

The standard integrated circuit technology has been developed to design and fabricate new innovative planar multi-junction solar cell chips for concentrated sunlight applications. This 1 cm x 1 cm cell consisted of several voltage generating regions called unit cells which were internally connected in series within a single chip resulting in high open circuit voltages. Typical open-circuit voltages of 3.6 V and short-circuit currents of 90 ma were obtained at 80 AM1 suns. A dramatic increase in both short circuit current and open circuit voltage with increased light levels was observed.

Valco, G. J.↗
NASA NTRS1991

High voltage thermally diffused p(+)n solar cells

The possibility of fabricating thermally diffused p(+)n InP solar-cells with high open-circuit voltage without sacrificing the short circuit current is discussed. The p(+)n InP junctions were formed by Cd and Zn diffusion through a 3-5-nm-thick anodic or chemical phosphorus-rich oxide cap layer grown on n:InP:S (with ND-NA = 3.5 x 10 exp 16 and 4.5 x 10 exp 17/cu cm) Czochralski LEC-grown substrates. After thinning the emitter from its initial thickness of 1 to 2.5 micron down to 0.06-0.15 micron, the maximum efficiency was found when the emitter was 0.2 to 0.3 micron thick. Typical AM0, 25 C values of 854-860 mV were achieved for Voc, Jsc values were from 25.9 to 29.1 mA/sq cm using only the P-rich passivating layer left after the thinning process as an antireflection coating.

Faur, M.↗
NASA NTRS2006

High Power, High Voltage Electric Power System for Electric Propulsion

This paper provides an overview of the 30 KW, 600 V MRHE power subsystem. Descriptions of the power subsystem elements, the mode of power transfer, and power and mass estimates are presented. A direct-drive architecture for electric propulsion is considered which reduces mass and complexity. Solar arrays with concentrators are used for increased efficiency. Finally, the challenges due to the environment of a hypothetical lunar mission as well as due to the advanced technologies considered are outlined.

direct drives↗
NASA NTRS1972

High voltage and current, gate assisted, turn-off thyristor development

An improved high speed power switch with unique turn-off capability was developed. This gate assisted turn-off thyristor (GATT) was rated 1000 volts and 100 amperes with turn-off times of 2 microseconds. Fifty units were delivered for evaluation. In addition, test circuits designed to relate to the series inverter application were built and demonstrated. In the course of this work it was determined that the basic device design is adequate to meet the static characteristics and dynamic turn-off specification. It was further determined that the turn-on specification is critically dependent on the gate drive circuit due to the distributive nature of the cathode-gate geometry. Future work should emphasize design modifications which reduce the gate current required for fast turn-on, thereby opening the way to higher power (current) devices.

Nowalk, T. P.↗
NASA NTRS1982

Planar multijunction high voltage solar cell chip

A new innovative planar multijunction solar cell chip for concentrated sunlight applications is proposed. The chip consists of many voltage-generating regions, called unit cells, which are connected in series within a single silicon wafer, thereby providing a high open-circuit voltage at multiple sun illumination levels. The unit cells are fabricated on 75 micron thick p-type single crystal silicon substrate. Each chip consists of 1.42 x 9.63 mm n(+)/p collecting junctions on the back of the wafer, while the illuminated front surface area is divided into 0.3 micron deep n(+) regions. The fabrication sequence includes standard degreasing and cleaning procedures, double-sided alignment photomasking, introduction of boron and phosphorus impurities, and photolithography. The open circuit voltage of the chip increased rapidly with illumination up to about 4 AM1 suns, and then began to saturate at the sum of the individual unit cell voltages of 3.5 above 4 AM1 suns. A short circuit density per unit cell of 300 mA/sq cm at 20 AM1 suns was observed.

Valco, G. J.↗
NASA NTRS1981

Fabrication of multijunction high voltage concentrator solar cells by integrated circuit technology

Standard integrated circuit technology has been developed for the design and fabrication of planar multijunction (PMJ) solar cell chips. Each 1 cm x 1 cm solar chip consisted of six n(+)/p, back contacted, internally series interconnected unit cells. These high open circuit voltage solar cells were fabricated on 2 ohm-cm, p-type 75 microns thick, silicon substrates. A five photomask level process employing contact photolithography was used to pattern for boron diffusions, phorphorus diffusions, and contact metallization. Fabricated devices demonstrated an open circuit voltage of 3.6 volts and a short circuit current of 90 mA at 80 AMl suns. An equivalent circuit model of the planar multi-junction solar cell was developed.

Valco, G. J.↗
NASA NTRS1968

High-voltage pulse generator developed for wide-gap spark chambers

Low-inductance, high-capacitance Marx pulse generator provides for minimization of internal inductance and suppression of external electromagnetic radiation. The spark gaps of the generator are enclosed in a pressurized nitrogen atmosphere which allows the charging voltage to be varied by changing the nitrogen pressure.

Keller, L. P.↗
NASA NTRS1982

Surface effects in high voltage silicon solar cells

The surface of low-resistivity silicon solar cells appears to be a major source of dark diffusion current. This region, consisting of the interface and the adjacent heavily doped layer, therefore, prevents attainment of the high open-circuit voltages expected from these cells. This paper describes the experimental effort carried out to reduce the various contributions of dark current from the surface. Analysis of results from this effort points to means of improving cell voltages by changing processing and structures.

Meulenberg, A.↗
NASA NTRS2010

Reliability of High-Voltage Tantalum Capacitors. Parts 3 and 4)

Weibull grading test is a powerful technique that allows selection and reliability rating of solid tantalum capacitors for military and space applications. However, inaccuracies in the existing method and non-adequate acceleration factors can result in significant, up to three orders of magnitude, errors in the calculated failure rate of capacitors. This paper analyzes deficiencies of the existing technique and recommends more accurate method of calculations. A physical model presenting failures of tantalum capacitors as time-dependent-dielectric-breakdown is used to determine voltage and temperature acceleration factors and select adequate Weibull grading test conditions. This model is verified by highly accelerated life testing (HALT) at different temperature and voltage conditions for three types of solid chip tantalum capacitors. It is shown that parameters of the model and acceleration factors can be calculated using a general log-linear relationship for the characteristic life with two stress levels.

Teverovsky, Alexander↗
NASA NTRS2005

High-voltage Array Ground Test for Direct-drive Solar Electric Propulsion

Development is underway on a unique high-power solar concentrator array called Stretched Lens Array (SLA) for direct drive electric propulsion. These SLA performance attributes closely match the critical needs of solar electric propulsion (SEP) systems, which may be used for "space tugs" to fuel-efficiently transport cargo from low earth orbit (LEO) to low lunar orbit (LLO), in support of NASA s robotic and human exploration missions. Later SEP systems may similarly transport cargo from the earth-moon neighborhood to the Mars neighborhood. This paper will describe the SLA SEP technology, discuss ground tests already completed, and present plans for future ground tests and future flight tests of SLA SEP systems.

Howell, Joe T.↗
NASA NTRS1979

NASCAP modelling of high-voltage power system interactions with space charged-particle environments

A simple space power system operating in geosynchronous orbit was analyzed. This system consisted of two solar array wings and a central body. Each solar array wing was considered to be divided into three regions operating at 2000 volts. The center body was considered to be an electrical ground with the array voltages both positive and negative relative to ground. The system was analyzed for both a normal environment and a moderate geomagnetic substorm environment. Initial results indicate a high probability of arcing at the interconnects on the negative operating voltage wing. The dielectric strength of the substrate may be exceeded giving rise to breakdown in the bulk of the material. The geomagnetic substorm did not seem to increase the electrical gradients at the interconnects on the negative operating voltage wing but did increase the gradients on the positive operating voltage wing which could result in increased coupling current losses.

Stevens, N. J.↗
NASA NTRS1978

An electro-optic, high-voltage, transient probe

A newly developed electro-optic voltage transducer is described. It is capable of measuring 30 ns rise time, floating or single-ended, 0 to 20 kV transients in a high noise environment such as a fast discharge laser or energetic switch system. The voltage transient is detected by a specially developed resistor in series with a light emitting diode. The light output (proportional to voltage) is transmitted remotely via a fiber-optic cable to a detector and recorder. Typical signals and comparison with commercial probe system signals are described.

Posta, S. J.↗
NASA NTRS1988

High voltage gas isolator

An isolator is provided which has an inlet at ground electrical potential which receives gas, and which has an outlet at a high electrical potential through which gas is discharged, the isolator being compactly and simply constructed while providing a long narrow path that minimizes the possibility of electrical breakdown through the gas. The isolator includes a first element forming a cylindrical core and a cup-shaped second element forming a sleeve portion that closely receives the core. The core has a helical groove on its outside to form a passage between the groove and the inner walls of the sleeve. The core also has a vertical hole extending to the bottom of the core and a radial groove in the bottom of the core that extends between the hole and the bottom of the helical groove.

Brophy, John R.↗
NASA NTRS1994

High-voltage electron collection by a spherical satellite

The numerical solution to the cold electron flow equations is presented for the region surrounding an ionospheric satellite at high positive potential. The momentum, continuity, and Poisson equations are solved simultaneously for satellite potentials of 1000, 10,000, 30,000, and 100,000 kT(kT = 0.17 eV). The electron velocity vectors in the sheath region are presented. The electron current density to the satellite surface is also reported. Electrons impact the satellite surface with average velocity vectors having angles of incidence (relative to the surface normal) that increase from the satellite's magnetic pole to equator. A toroidal flow develops in the vicinity of the magnetic equator and expands away from the satellite surface as the surface potential is increased. The current density to the satellite surface increases with increasing satellite potential and decreases with increasing polar angle.

Sheldon, J. W.↗