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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Changes in impedance of Ni electrodes upon standing and cycling

Impedances of Ni electrodes vary with many factors including voltage, cycling, and manufacturer. However, results from Ni/H2 cells being tested for Space Station Freedom show that consistent results are obtained within a group of cells from the same manufacturer if the cells are cycled and stored in the same manner. Impedance changes with storage and cycling are being investigated. Impedances are low in the fully charged state but rise abruptly by several orders of magnitude at a voltage corresponding to a very low state-of-charge. After standing for several months, this increase occurred at a higher voltage, consistent with an increase in structural order during storage which hinders diffusion of protons and reduces high rate capacity. Early measurements on the effects of cycling on Ni/H2 cells being tested for Space Station Freedom show differences between cells from different manufacturers.

Reid, Margaret A.↗
NASA NTRS1990

Validity of the two-level model for Viterbi decoder gap-cycle performance

A two-level model has previously been proposed for approximating the performance of a Viterbi decoder which encounters data received with periodically varying signal-to-noise ratio. Such cyclically gapped data is obtained from the Very Large Array (VLA), either operating as a stand-alone system or arrayed with Goldstone. This approximate model predicts that the decoder error rate will vary periodically between two discrete levels with the same period as the gap cycle. It further predicts that the length of the gapped portion of the decoder error cycle for a constraint length K decoder will be about K-1 bits shorter than the actual duration of the gap. The two-level model for Viterbi decoder performance with gapped data is subjected to detailed validation tests. Curves showing the cyclical behavior of the decoder error burst statistics are compared with the simple square-wave cycles predicted by the model. The validity of the model depends on a parameter often considered irrelevant in the analysis of Viterbi decoder performance, the overall scaling of the received signal or the decoder's branch-metrics. Three scaling alternatives are examined: optimum branch-metric scaling and constant branch-metric scaling combined with either constant noise-level scaling or constant signal-level scaling. The simulated decoder error cycle curves roughly verify the accuracy of the two-level model for both the case of optimum branch-metric scaling and the case of constant branch-metric scaling combined with constant noise-level scaling. However, the model is not accurate for the case of constant branch-metric scaling combined with constant signal-level scaling.

Dolinar, S.↗
NASA NTRS1989

Electrochemical behavior of heavily cycled nickel electrodes in Ni/H2 cells containing electrolytes of various KOH concentrations

A study has been made of charge and discharge voltage changes with cycling of Ni/H2 cells containing electrolytes of various KOH concentrations. A study has also been made of electrochemical behavior of the nickel electrodes from the cycled Ni/H2 cells as a function of overcharge amounts. Discharge voltages depressed gradually with cycling for cells having high KOH concentrations (31 to 36 percent), but the voltages increased for those having low KOH concentrations (21 to 26 percent). To determine if there was a crystallographic change of the active material due to cycling, electrochemical behavior of nickel electrodes was studied in an electrolyte flooded cell containing either 31 or 26 percent KOH electrolyte as a function of the amount of overcharge. The changes in discharge voltage appear to indicate crystal structure changes of active material from gamma-phase to beta-phase in low KOH concentrations, and vice versa in high KOH concentration.

Lim, H. S.↗
NASA NTRS1990

Dual-peak solar cycle distribution of intense geomagnetic storms

This paper studies the features of the solar cycle distribution of intense storms (Dst) during cycles 20 and 21 (1965-1985). For these cycles, the distribution of intense storms (including moderate events for this time interval) in terms of Dst values below -50 nT, showed a dual-peak distribution, providing evidence for another enhancement of the intense storm distribution at the late ascending phase of the cycle. The origin of the dual-peak distribution of intense storms is associated with a similar dual-peak distribution obtained for large-amplitude and long-duration values of the negative Bz component of the IMF, computed for the interval 1970-1981.

Gonzalez, W. D.↗
NASA NTRS1990

Solar proton events during solar cycles 19, 20, and 21

Earlier studies based on a single solar cycle had resulted in a sharp division of events into 'ordinary' and 'anomalously large' events. Two such entirely separate distributions imply two entirely separate acceleration mechanisms, one common and the other very rare. The sharp division is neither required nor justified by this larger sample. Instead the event intensity forms a smooth distribution for intensities up to the largest observed implying that any second acceleration mechanism cannot be rare. Also, a clear bimodal variation of annual integrated flux with solar cycle phase but no statistically significant tendency for the large events to avoid sunspot maximum is found. There is almost no relation between the maximum sunspot number in a solar cycle and the solar cycle integrated flux. It is also found that for annual sunspot numbers greater than 35 there is no relation whatsoever between the annual sunspot numbers and annual integrated flux.

Feynman, J.↗
NASA NTRS1990

Undeveloped rocket cycle applications to advanced earth-to-orbit transportation

The application of undeveloped rocket engine cycles to advanced manned launch vehicles is assessed. Two undeveloped rocket cycles are selected, the split expander cycle and the full flow staged-combustion cycle, for detailed engine description and comparison with more mainstream advanced vehicle engine candidates. In the formulation of the Next Manned Transportation System, propulsion is a key area for cost reduction because of the high cost elements associated with the current Space Transportation Syystem.

Kramer, R. D.↗
NASA NTRS1990

On the maximum rate of change in sunspot number growth and the size of the sunspot cycle

Statistically significant correlations exist between the size (maximum amplitude) of the sunspot cycle and, especially, the maximum value of the rate of rise during the ascending portion of the sunspot cycle, where the rate of rise is computed either as the difference in the month-to-month smoothed sunspot number values or as the 'average rate of growth' in smoothed sunspot number from sunspot minimum. Based on the observed values of these quantities (equal to 10.6 and 4.63, respectively) as of early 1989, it is inferred that cycle 22's maximum amplitude will be about 175 + or - 30 or 185 + or - 10, respectively, where the error bars represent approximately twice the average error found during cycles 10-21 from the two fits.

Wilson, Robert M.↗
NASA NTRS1990

Solar Cycle Modulation of Total Irradiance: an Empirical Model from 1874 to 1988

Evidence acquired during the past decade indicates that over time scales of the solar cycle, enhanced emission from bright solar faculae cause significant variations in the sun's total irradiance even though, on shorter time scales, the most pronounced variations are those resulting from the passage of dark sunspots across the solar disc. An empirical model which accounts for the competing effects of dark sunspots and bright faculae has been developed from the available radiometry in cycle 21, and extended back to the beginning of solar cycle 12. According to this model, the largest 11-year modulation of total irradiance during the C20th occurred in the most recent cycle 21.

Lean, J.↗
NASA NTRS1991

Thermal cycle testing of Space Station Freedom solar array blanket coupons

Lewis Research Center is presently conducting thermal cycle testing of solar array blanket coupons that represent the baseline design for Space Station Freedom. Four coupons were fabricated as part of the Photovoltaic Array Environment Protection (PAEP) Program, NAS 3-25079, at Lockheed Missile and Space Company. The objective of the testing is to demonstrate the durability or operational lifetime of the solar array welded interconnect design within the durability or operational lifetime of the solar array welded interconnect design within a low earth orbit (LEO) thermal cycling environment. Secondary objectives include the observation and identification of potential failure modes and effects that may occur within the solar array blanket coupons as a result of thermal cycling. The objectives, test articles, test chamber, performance evaluation, test requirements, and test results are presented for the successful completion of 60,000 thermal cycles.

Scheiman, David A.↗
NASA NTRS1990

The role of the seasonal cycle in the quasi-biennial oscillation of ozone

The evidence for seasonal synchronization of the ozone quasi-biennial oscillation (QBO) is reviewed, showing how this behavior is not expected on the basis of QBO transport alone but may arise due to the seasonal cycle. Near the equator, the ozone QBO is closely tied to the dynamical QBO and exhibits the same period as that oscillation. Maximum column ozone is attained soon after the transition to westerlies at 50 mb. In the subtropics, the ozone QBO is strongly tied to the seasonal cycle, with anomalies centered in the winter-spring season irrespective of QBO phase. These anomalies result from the interaction of the annual cycle and the QBO. Numerical model results are reported which establish that hemispheric asymmetry in the ozone QBO does not require seasonal asymmetries in the strength or location of the Hadley circulation. The fundamental cause of hemispheric asymmetry in the subtropical ozone QBO is the timing of equatorial, ozone anomalies relative to the seasonal cycle.

Gray, Lesley J.↗
NASA NTRS1991

Solar cycle variations in the size and shape of the magnetopause

The 10 years of the ISEE 1 and 2 mission covering much of solar cycle 21 and the beginning of solar cycle 22 make it possible to study the position, shape, and motion of the magnetopause throughout the course of changing solar activity. The size and shape of the magnetopause were determined for each observing season using the ISEE 1 and 2 magnetometer data IMP 8 data were used to monitor the solar wind changes with the solar cycle. During the 1979-1980 season, at solar maximum, the solar wind dynamic pressure was at its lowest values, and, at solar minimum, the solar wind pressure was at its largest values, more than double the value in the 1979-1980 season. During this solar cycle, the magnetopause was about 0.5 R(E) farther when the interplanetary magnetic field (IMF) was strongly northward, than when strongly southward. Both standoff distance values are fround to be smaller than the value found by Fairfield (1971). The standoff distance of the magnetopause for northward IMF is anticorrelated with the solar wind pressure. However, the standoff distance for southward IMF seems relatively insensitive to solar wind dynamic pressure.

Petrinec, S. P.↗
NASA NTRS1992

Single-Cycle Versus Multicycle Proof Testing

Report compares single-cycle with multiple-cycle mechanical-stress tests of parts under mechanical stresses. Objective of proof testing: to screen out gross manufacturing or material deficiencies and provide additional assurance of quality. Report concludes that changes in distribution of crack sizes during multicycle proof testing depend on initial distribution, number of cycles, relationship between resistance of material and elastic/plastic fracture-mechanics parameter, relationship between load control and displacement control, and magnitude of applied load or displacement. Whether single-cycle or multicycle testing used depends on shape, material, and technique of fabrication of components tested.

Hudak, S. J., Jr.↗
NASA NTRS1992

Synergistic effects of ultraviolet radiation, thermal cycling, and atomic oxygen on altered and coated Kapton surfaces

The photovoltaic (PV) power system for Space Station Freedom (SSF) uses solar array blankets which provide structural support for the solar cells and house the electrical interconnections. In the low Earth orbital (LEO) environment where SSF will be located, surfaces will be exposed to potentially damaging environmental conditions including solar ultraviolet (UV) radiation, thermal cycling, and atomic oxygen. It is necessary to use ground based tests to determine how these environmental conditions would affect the mass loss and optical properties of candidate SSF blanket materials. Silicone containing, silicone coated, and SiO(x) coated polyimide film materials were exposed to simulated LEO environmental conditions to determine there durability and whether the environmental conditions of UV, thermal cycling and oxygen atoms act synergistically on these materials. A candidate PV blanket material called AOR Kapton, a polysiloxane polyimide cast from a solution mixture, shows an improvement in durability to oxygen atoms erosion after exposure to UV radiation or thermal cycling combined with UV radiation. This may indicate that the environmental conditions react synergistically with this material, and the damage predicted by exposure to atomic oxygen alone is more severe than that which would occur in LEO where atomic oxygen, thermal cycling and UV radiation are present together.

Dever, Joyce A.↗
NASA NTRS1991

The effect of temperature cycling typical of low earth orbit satellites on thin films of YBa2Cu3O(7-x)

Thin films of YBa2Cu3O(7-x) (YBCO) were temperature cycled to simulate conditions of a low earth orbit satellite. In one series of tests, epitaxial and polycrystalline YBCO films were cycled between temperatures of +/- 80 C in vacuum and in nitrogen for hundreds of cycles. The room temperature resistance of an epitaxial YBCO film increased by about 10 percent, but the superconducting transition temperature was unchanged. The largest changes were for a polycrystalline YBCO film on oxidized silicon with a zirconia buffer layer, for which the transition temperature decreased by 3 K. An extended test was carried out for epitaxial films. After 3200 cycles (corresponding to about 230 days in space), transition temperatures and critical current densities remained unchanged.

Mogro-Campero, A.↗
NASA NTRS1992

Results of deep DoD life cycle tests at high rates on 12Ah NiCd cells

A 12 Ah Nickel-Cadmium (NiCd) Low Earth Orbit (LEO) life cycle test that induced 47 percent more deep Depth Of Discharge cycles by mixing them with shallow DOD cycles is discussed. The test showed how aggressive recharging to a C/D ratio of 1.15 nearly doubled performance over cycling below a C/D of 1.11.

Panneton, Paul E.↗
NASA NTRS1992

Practical considerations in designing the engine cycle

When it is required to define the cycle parameters and calculate the performance of a real engine, there are numerous practical constraints that need to be taken into account. These fall into two main categories: the limitations of available component technologies, and the operational considerations that are dependent on aircraft application. The lecture discusses the main technology limiters and indicates how they are incorporated into the cycle definition process. Operational factors include the extent of the intended flight envelope and range of critical flight conditions for which performance must be assured, and the balance to be struck between minimising fuel consumption, maximising installed power and constraining costs of ownership. Taking these technology and operational influences into account, the basic cycle characteristics and approach to cycle choice are examined for three main classes of aircraft: subsonic transports, military combat aircraft and helicopters.

M G Philpot↗
NASA NTRS1992

The Mars water cycle at other epochs: History of the polar caps and layered terrain

The atmospheric water cycle at the present epoch involves summertime sublimation of water from the north polar cap, transport of water through the atmosphere, and condensation on one or both winter CO2 caps. Exchange with the regolith is important seasonally, but the water content of the atmosphere appears to be controlled by the polar caps. The net annual transport through the atmosphere, integrated over long timescales, must be the driving force behind the long-term evolution of the polar caps; clearly, this feeds back into the evolution of the layered terrain. We have investigated the behavior of the seasonal water cycle and the net integrated behavior at the pole for the last 10 exp 7 years. Our model of the water cycle includes the solar input, CO2 condensation and sublimation, and summertime water sublimation through the seasonal cycles, and incorporates the long-term variations in the orbital elements describing the Martian orbit.

Jakosky, Bruce M.↗
NASA NTRS1992

Synergistic effects of ultraviolet radiation, thermal cycling and atomic oxygen on altered and coated Kapton surfaces

The photovoltaic (PV) power system for Space Station Freedom (SSF) uses solar array blankets which provide structural support for the solar cells and house the electrical interconnections. In the low earth orbital (LEO) environment where SSF will be located, surfaces will be exposed to potentially damaging environmental conditions including solar ultraviolet (UV) radiation, thermal cycling, and atomic oxygen. It is necessary to use ground based tests to determine how these environmental conditions would affect the mass loss and optical properties of candidate SSF blanket materials. Silicone containing, silicone coated, and SiO(x) coated polyimide film materials were exposed to simulated LEO environmental conditions to determine their durability and whether the environmental conditions of UV, thermal cycling and oxygen atoms act synergistically on these materials. A candidate PV blanket material called AOR Kapton, a polysiloxane polyimide cast from a solution mixture, shows an improvement in durability to oxygen atoms erosion after exposure to UV radiation or thermal cycling combined with UV radiation. This may indicate that the environmental conditions react synergistically with this material, and the damage predicted by exposure to atomic oxygen alone is more severe than that which would occur in LEO where atomic oxygen, thermal cycling and UV radiation are present together.

Dever, Joyce A.↗