Research and development of silicon solar cells optimized for space exploration power systems Quarterly report, 1 Apr. - 30 Jun. 1970
Optimized silicon solar cell development for spacecraft with near-sun missions
Iles, P. A.↗
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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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Simulation of space radiation effects on polyimide film materials for high temperature applications
Space environment effects on candidate materials for the solar sail film are determined. Polymers, including metallized polyimides that might be suitable solar radiation receivers, were exposed to combined proton and solar electromagnetic radiation. Each test sample was weighted, to simulate the tension on the polymer when it is stretched into near-planar shape while receiving solar radiation. Exposure rates up to 16 times that expected in Earth orbit were employed, to simulate near-sun solar sailing conditions. Sample appearance, elongation, and shrinkage were monitored, noted, and documented in situ. Thermosetting polyimides showed less degradation or visual change in appearance than thermoplastics.
Fogdall, L. B.↗
Direct observation of the latitudinal extent of a high-speed stream in the solar wind
The latitudinal boundaries of stationary fast solar wind streams emerging from equatorward extensions of the sun's polar coronal holes are studied. Simultaneous data from the Helios 1 and Imp spacecraft at different heliographic latitudes are compared. The measured latitudinal speed gradient of 30 km/s/deg shows that large angular speed gradients occur at the leading edges of fast streams and also with respect to latitude. The data indicate that longitudinal speed gradients are steeper near 0.3 AU than at 1.0 AU. Generally, regions with large angular speed gradients are observed to separate fast streams from the surrounding slower plasma. This suggests the existence of mechanisms which diminish longitudinal speed gradients as the plasma travels toward 1.0 AU. It also seems that the distribution of solar wind speeds on a near-sun spherical surface has large mesalike high-speed regions. Comparisons of Helios 1 and Imp data with corona observations supports the hypothesis that high-speed solar wind streams emerge from coronal holes.
Schwenn, R.↗
Spacecraft radio scattering observations of the power spectrum of electron density fluctuations in the solar wind
Solar wind electron density power spectra in the solar equatorial region are inferred from observations of phase scintillations and spectral broadening made with the Viking, Helios, and Pioneer spacecraft. The heliocentric distance range covered is 2-215 solar radii and for some observations close to the sun the spectra extend to fluctuation frequencies as high as 100 Hz. For heliocentric distances of about 20 solar radii the equivalent spacecraft-measured one-dimensional density spectrum is well modeled by a single power law in the frequency range 0.0001-0.05 Hz. The flattening of the density spectrum within 20 solar radii is presumably associated with energy deposition in the near-sun region and acceleration of the solar wind.
Woo, R.↗
Planetary spacecraft pointing and control - The next 20 years
Pointing and control systems recommended for NASA planetary exploration missions of the next twenty years are discussed. The functional and operational requirements and design constraints imposed on the driving control system by the mission and science goals of the spacecraft are examined. Criteria for the selection of a pointing and control system type (spin, dual-spin, three-axis active or momentum bias) are outlined, including payload functional characteristics, orbital characteristics, vehicle configuration and mission duration, and candidate system types proposed for preliminary survey, detailed remote observation, deep space close scrutiny, near-sun close scrutiny and sample return missions are indicated. Trends in control system design are discussed, and key enabling technology areas that will require additional or new development are considered, with particular emphasis on laser and fiber optics gyros, CCD arrays and DMA signal/power transmission, bearings and motor technologies, directed at three-axis active and dual-spin implementations.
Mcglinchey, L. F.↗
Nuclear electric propulsion /NEP/ spacecraft for the outer planet orbiter mission
The design, operating features, and a possible Neptune orbit for the spacecraft powered by the SP-100 nuclear electric propulsion (NEP) system under study by NASA and the DOE are described. The system features a reactor and a payload situated on opposite ends of a 0.5 m diam, 11 m long astromast. Mercury-ion thrusters are located beneath the reactor for side thrusting, and no contamination of the payload or obstruction of the viewing angles for scientific objectives occurs with the system, which would not degrade in performance even under high insolation during near-sun maneuvers. Results of a theoretical study of earth escapes are presented to show that an NEP powered spiral trajectory out of a 700 km Shuttle orbit and using a Triton gravity assist would be superior to departing from a 300 km orbit with a Centaur boost. The mission profile includes a 1249 kg Galileo payload. The SP-100 has a 1.4 MWth reactor with UO2 fuel tiles and weighs 19,904 kg.
Garrison, P. W.↗
The effect of different solar simulators on the measurement of short-circuit current temperature coefficients
Gallium arsenide solar cells are considered for several high temperature missions in space. Both near-Sun and concentrator missions could involve cell temperatures on the order of 200 C. Performance measurements of cells at elevated temperatures are usually made using simulated sunlight and a matched reference cell. Due to the change in bandgap with increasing temperature at portions of the spectrum where considerable simulated irradiance is present, there are significant differences in measured short circuit current at elevated temperatures among different simulators. To illustrate this, both experimental and theoretical data are presented for gallium arsenide cells.
Curtis, H. B.↗
Doppler scintillation observations of interplanetary shocks within 0.3 AU
It is pointed out that more definitive shock velocity observations near the sun are needed for an improved determination of the extent of shock deceleration from the sun to earth. Woo and Armstrong (1981) have demonstrated the use of radio scattering and scintillation observations, using spacecraft signals, for measuring interplanetary shock waves near the sun. Woo and Armstrong provided the first near-sun profiles of solar wind speed and electron density fluctuation for a shock wave produced by a solar flare. The present investigation has the objective to demonstrate the use of Doppler or phase scintillations for monitoring and observing interplanetary shocks. It is also shown that Doppler noise, a parameter which is routinely observed and recorded by the NASA Deep Space Network, is essentially a measure of Doppler scintillations.
Woo, R.↗
Thermoluminescence of Antarctic meteorites: A rapid screening technique for terrestrial age estimation, pairing studies and identification of specimens with unusual prefall histories
Thermoluminescence (TL) is a promising technique for rapid screening of the large numbers of Antarctic meteorites, permitting identification of interesting specimens that can then be studied in detail by other, more definite techniques. Specifically, TL permits determination of rough terrestrial age, identification of potential paired groups and location of specimens with unusual pre-fall histories. Meteorites with long terrestrial ages are particularly valuable for studying transport and weathering mechanisms. Pairing studies are possible because TL variations among meteorites are large compared to variations within individual objects, especially for natural TL. Available TL data for several L3 fragments, three of which were paired by other techniques, are presented as an example of the use of TL parameters in pairing studies. Additional TL measurements, specifically a blind test, are recommended to satisfactorily establish the reliability of this pairing property. The TL measurements also identify fragments with unusual pre-fall histories, such an near-Sun orbits.
Sutton, S. R.↗
Solar events and their influence on the interplanetary medium
Aspects of a workshop on Solar events and their influence on the interplanetary medium, held in September 1986, are reviewed, the goal of which was to foster interactions among colleagues, leading to an improved understanding of the unified relationship between solar events and interplanetary disturbances. The workshop consisted of three working groups: (1) flares, eruptives, and other near-Sun activity; (2) coronal mass ejections; and (3) interplanetary events. Each group discussed topics distributed in advance. The flares-eruptives group members agreed that pre-event energy is stored in stressed/sheared magnetic fields, but could not agree that flares and other eruptive events (e.g., eruptive solar prominences) are aspects of the same physical phenomenon. In the coronal mass ejection group, general agreement was reached on the presence of prominences in CMEs, and that they have a significant three-dimensional structure. Some topics identified for further research were the aftermath of CMEs (streamer deflections, transient coronal holes, possible disconnections), identification of the leading edge of CMEs, and studies of the range and prevalence of CME mass sizes and energies.
Joselyn, Joann↗
Long-lived thermal control materials for high temperature and deep space applications
Considerable effort has been put into developing thermal-control materials for the Galileo space-craft. This paper presents a summary of these findings to date with emphasis on requirements, testing and results for the post-Challenger Galileo mission. Polyimide film (Kapton), due to its inherent stability in vacuum, UV, and radiation environments, combined with good mechanical properties over a large temperature range, has been the preferred substrate for spacecraft thermal control materials. Composite outer layers, using Kapton substrates, can be fabricated to meet the requirements of severe space environments. Included in the processing of Kapton-based composite outer layers can be the deposition of metal oxide, metallic and/or polymeric thin-film coatings to provide desirable electrical, optical and thermo-optical properties. In addition, reinforcement of Kapton substrates with fabrics and films is done to improve mechanical properties. Also these substrates can be filled with varying amounts of carbon to achieve particular electrical properties. The investigation and material development reported on here has led to improved thermo-gravimetric stability, surface conductivity, RF transparency, radiation and UV stability, flammability and handle-ability of outer layer thermal control materials for deep space and near-sun spacecraft. Designing, testing, and qualifying composite thermal-control film materials to meet the requirements of the Galileo spacecraft is the scope of this paper.
Whitt, Robin↗
MHD study of temporal and spatial evolution of simulated interplanetary shocks in the ecliptic plane within 1 AU
The present parametric study of interplanetary shock propagation to 1 AU uses a two- and-one-half-dimensional MHD time-dependent model whose input conditions encompass initial shock velocity, driving-pulse duration, and pulse width at the near-sun position of 18 solar radii. It is found that, for input pulses with modest angular width and temporal duration, the propagation of the resulting interplanetary fast-forward shock waves primarily depends on the net input energy. While the properties of the reverse shocks are also a function of input energy, they depend on the specific values of the input pulse shock velocity, width, and duration.
Smith, Zdenka↗
Propagation of solar flare-associated interplanetary shock waves in the heliospheric meridional plane
An analysis is conducted for 149 flare-associated shock wave events based on interplanetary scintillation observational data. All of the flare-associated shock waves tend to propagate toward the low latitude region near the solar equator for flares that are located in both the solar Northern and Southern Hemispheres. Also, the fastest propagation directions tend toward the heliospheric current sheet near 1 AU. This tendency is caused by the dynamic action of near-sun magnetic forces on the ejected coronal plasma that traverses the helmet-like magnetic topologies near the sun outward to the classical topology that is essentially parallel to the heliospheric current sheet.
Wei, Fengsi↗
Overview of cosmic rays, solar and interplanetary physics research (1987-1990)
A brief survey of recent U.S. investigations in the field of heliospheric plasmas and their manifestations is presented, introducing the following collection of detailed reviews (accessions A91-46959 to A91-46964). Topics examined include the large-scale structure of interplanetary plasmas, models of Galactic cosmic-ray production and propagation, solar-wind turbulence, long-period solar-terrestrial variability, the possible relation between solar-neutrino counts and the sunspot cycle, X-ray studies of solar flares and their implications for solar processes, and the near-sun magnetic field.
Jokipii, J. R.↗
Turbulence and waves in the solar wind
Studies of turbulence and waves in the solar wind is discussed. Consideration is given to the observations and theory concerning the origin and evolution of interplanetary MHD fluctuations and to the observations, theory, and simulations of compressive fluctuations. Particular attention is given to extrapolations to near-sun and polar fields regions. Results obtained on turbulence at comets and magnetic turbulence of low-frequency waves excited by unstable distributions of ions are discussed.
Roberts, D. A.↗
Observations of the electron density spectrum near the sun during spectral broadening transients
We present high-time resolution spectral broadening data for several transients caused by propagating interplanetary disturbances observed inside 20 solar radii. The results show that the shape and level of the ambient near-sun electron density spectrum undergoes abrupt and substantial change during passage of the disturbance. The steepening of the spectrum to near the Kolmogorov value suggests fully-developed inertial-range turbulence in the wake of the interplanetary disturbance.
Woo, R.↗
Solar cycle variation of interplanetary disturbances observed as Doppler scintillation transients
Interplanetary disturbances characterized by plasma that is more turbulence and/or moves faster than the background solar wind are readily defected as transients in Doppler scintillation measurements of the near-Sun solar wind. Systematic analysis of over 23,000 hours of Pioneer Venus Orbiter Doppler measurements obtained inside 0.5 AU during 1979-1987 have made it possible for the first time to investigate the frequency of occurrence of Doppler scintillation transients under solar minimum conditions and to determine its dependence on solar cycle. On the basis of a total of 142 transients, Doppler scintillation transient rates vary from a high of 0.22 in 1979 (one every 4.6 days) to a low of 0.077 transients/d in 1986 (one every 13 days), a decrease by almost a factor of 3 from solar maximum to solar minimum. This solar cycle variation, the strongest yet of any solar wind Doppler scintillation property, is highly correlated with both solar activity characterized by sunspot number and the coronal mass ejection rates deduced from Solswind and Solar Maximum Mission (SMM) coronagraph observations. These results indicate that coronal mass ejections and Doppler scintillation transients are closely related not just during solar maximum, as occasional individual comparisons have shown in the past, but throughout the entire solar cycle, and strengthen the notation that the Doppler scintillation and optical transients are different manifestations of the same physical phenomenon. The magnitudes of the transients, as described by the ratio of peak to pretransient scintillation levels (EF for enhancement factor), and their distribution iwth heliocentric distance also vary with solar cycle. While EF tends to diminish with increasing heliocentric distance during high solar activity, it is more evenly distributed during low solar activity. EF is also lower during solar minimum, as 13% of the transients during solar maximum have values exceeding 23, the highest EF observed during solar minimum. These results are consistent with the fact that occasional major fast-moving interplanetary shocks that are observed during solar maximum are very rate during solar minimum.
Woo, Richard↗
Solar Wind Speed Structure in the Inner Corona at 3-12 Ro
Estimates of solar wind speed obtained by Armstrong et al. [1986] based on 1983 VLA multiple-station intensity scintillation measurements inside 12 R(sub o) have been correlated with the electron density structure observed in white-light coronagraph measurements. The observed large- scale and apparently systematic speed variations are found to depend primarily on changes in heliographic latitude and longitude, which leads to the first results on large-scale speed structure in the acceleration region of the solar wind. Over an equatorial hole, solar wind speed is relatively steady, with peak-to-peak variations of 50 km/s and an average of 230 km/s. In contrast, the near-Sun flow speed across the streamer belt shows regular large-scale variations in the range of 100-300 km/s. Based on four groups of data, the gradient is 36 km/s per degree in heliocentric coordinates (corresponding to a rise of 260 km/s over a spatial distance on the Sun of two arcmin) with a standard deviation of 2.4 km/s per degree. The lowest speeds most likely coincide with the stalks of coronal streamers observed in white-light measurements. The detection of significant wind shear over the streamer belt is consistent with in situ and scintillation measurements showing that the density spectrum has a power-law form characteristic of fully developed turbulence over a much broader range of scales than in neighboring regions.
Woo, Richard↗