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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 505 records · Page 28
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NASA NTRS1981

The solar spectral irradiance 1200-3184 A near solar maximum - July 15, 1980

Results of a sounding rocket program designed to measure the total solar ultraviolet input to the upper atmosphere are presented. Two spectrometers, a far-ultraviolet (FUV) to cover 1160-1850 A, and a middle ultraviolet (MUV) to cover 1600-3184 A, were launched piggy-back on a Black Brant rocket to an altitude of 325 km on 7-15-1980. Tables of the detailed error budgets of the reclaimed instruments are provided. Comparisons are made with results of a 1979 flight, and of 1979 and 1980 flights with solar minimum results of Rottman (1981), and reveal significant solar spectral irradiance variability from solar minimum to maximum. MUV readings below 2100 A were 14% higher in 1980 and 14% lower in 1979 than Rottman's data, and it is concluded that a significant variability occurred at wavelengths less than 1800 A.

Mount, G. H.↗
NASA NTRS1981

Ultraviolet spectrometer and polarimeter for the Solar Maximum Mission

The detailed optical design of the Solar Maximum Mission-Ultraviolet Spectrometer and Polarimeter is discussed in conjunction with the scientific objectives that led to the design. The instrument consists of a 1.8-m effective focal length aplanatic Gregorian telescope followed by a 1-m Ebert spectrometer. The design of the Stokes polarimeter is also discussed.

Miller, M. S.↗
NASA NTRS1982

Development of an LSI maximum-likelihood convolutional decoder for advanced forward error correction capability on the NASA 30/20 GHz program

The particular coding option identified as providing the best level of coding gain performance in an LSI-efficient implementation was the optimal constraint length five, rate one-half convolutional code. To determine the specific set of design parameters which optimally matches this decoder to the LSI constraints, a breadboard MCD (maximum-likelihood convolutional decoder) was fabricated and used to generate detailed performance trade-off data. The extensive performance testing data gathered during this design tradeoff study are summarized, and the functional and physical MCD chip characteristics are presented.

Clark, R. T.↗
NASA NTRS1982

Solar flare X-ray spectra from the Solar Maximum Mission Flat Crystal Spectrometer

High-resolution solar X-ray spectra obtained with the Flat Crystal Spectrometer aboard the Solar Maximum Mission from two solar flares and a nonflaring active region are analyzed. The 1-22 A region was observed during the flare on 1980 August 25, while smaller spectral regions were repeatedly covered during the 1980 November 5 flare. Voigt profiles were fitted to spectral lines to derive accurate wavelengths and to resolve blends. During the August 25 flare, 205 lines were found in the range 5.68-18.97 A, identifications being provided for all but 40 (mostly weak) lines. Upper limits to flare densities are derived from various line ratios, the hotter (about 10 to the 7th K) ions giving an electron density of less than 10 to the 12th per cu cm for the August 25 flare. Other observed line ratios (e.g., in Fe XVII and Mg XII) indicate a need for revisions in theoretical calculations.

Phillips, K. J. H.↗
NASA NTRS1982

Atmospheric ozone determination by solar occultation using the UV spectrometer on the Solar Maximum Mission

The UV spectrometer polarimeter instrument on the Solar Maximum Mission spacecraft has been used to measure ozone in the 53-75 km altitude interval by the technique of solar occultation. A 1 x 180 arcsec entrance aperture spectrometer with 0.04-A spectral resolution was employed. Resulting high-quality data are reduced by expressing measured UV attenuation as a Volterra integral equation. Solution of the equation is accomplished by expressing the integral in terms of a series representing the sum of ozone densities contained in concentric shells through tangent points separated by specified altitude increments. Sample ozone vs altitude profiles are presented for the equatorial region. These data show reproducibility to better than 10%. The density at 60 km is 7.3 + or - 0.15 x 10 to the 9th/cu cm for 2.5 deg latitude and longitudes between 81 and 105 deg west in September 1980. Density vs altitude profile exhibits changes in slope between 50 and 75 km.

Aikin, A. C.↗
NASA NTRS1982

Comparison of theoretically predicted and observed Solar Maximum Mission X-ray spectra for the 1980 April 13 and May 9 flares

A method for predicting the hard X-ray spectrum in the 10-100 keV range for compact flares during their initial rise is developed on the basis of a thermal model. Observations of the flares of 1980 April 13, 4:05 U.T., and 1980 May 9, 7:12 U.T. are given and their combined spectra from the Hard X-ray Burst Spectrometer and Hard X-ray Imaging Spectrometer on the Solar Maximum Mission are deduced. Constraints on the cross sectional area of the supposed emitting arch are obtained from data from the Hard X-ray Imaging Spectrometer. A power-law spectrum is predicted for the rise of the flare of April 13 for initial arch densities less than 10 to the 10th per cu cm and also for the flare of May 9 for initial arch densities less than 5.4 x 10 to the 10th per cu cm. In both cases power-law spectra are observed. Limitations and implications of these results are discussed.

Smith, D. F.↗
NASA NTRS1982

Solar maximum observatory repair mission

A description of the Solar Maximum Observatory and the operational status of its instrument systems is presented. The major science objectives which could be made possible with repairs to the spacecraft are defined. Hardware requirements and procedures for a repair mission are detailed. In general the mission involves: (1) the capture and control of the observatory in free flight by an astronaut in the manned manipulator unit; (2) berthing the observatory to the orbiter with the remote manipulator system; and (3) repairing the scientific instruments and replacing the attitude control system through extravehicular activity.

Kenney, G. P.↗
NASA NTRS1983

Solar coronal non-thermal processes (Solar Maximum Mission)

The Solar Maximum Mission was used to study solar coronal phenomena in hard X-radiation, since its instrument complement included the first solar hard X-ray telescope. Phenomena related to those discovered from OSO-5 and OSO-7 observations were emphasized.

Hudson, H. S.↗
NASA NTRS1982

A comparison of minimum distance and maximum likelihood techniques for proportion estimation

The estimation of mixing proportions P sub 1, P sub 2,...P sub m in the mixture density f(x) = the sum of the series P sub i F sub i(X) with i = 1 to M is often encountered in agricultural remote sensing problems in which case the p sub i's usually represent crop proportions. In these remote sensing applications, component densities f sub i(x) have typically been assumed to be normally distributed, and parameter estimation has been accomplished using maximum likelihood (ML) techniques. Minimum distance (MD) estimation is examined as an alternative to ML where, in this investigation, both procedures are based upon normal components. Results indicate that ML techniques are superior to MD when component distributions actually are normal, while MD estimation provides better estimates than ML under symmetric departures from normality. When component distributions are not symmetric, however, it is seen that neither of these normal based techniques provides satisfactory results.

Woodward, W. A.↗
NASA NTRS1983

Latitudinal (seasonal) variations in the thermospheric midnight temperature maximum - A tidal analysis

The temperature variations of the neutral gas in the thermosphere are considered as a function of local time and season, taking into account the latitude range from -17.5 deg to +17.5 deg and the altitude range from about 250 km to about 400 km. The temperature measurements were conducted in situ with the Neutral Atmospheric Temperature Experiment (NATE) on the Atmospheric Explorer E (AE-E) spacecraft during the time between December 1976 and January 1979. The altitude of the circular orbit of the spacecraft was gradually increased during this period from 250 to 400 km. A significant result of the reported analysis is the latitudinal (seasonal) variation observed in the semidiurnal and terdiurnal tides during solstice. It is found that this variation is responsible for the seasonal behavior of the midnight temperature maximum.

Herrero, F. A.↗
NASA NTRS1983

Observation of chromospheric evaporation during the Solar Maximum Mission

A study is presented of the upward motions of part of the soft X-ray emitting plasma using data for flares collected in 1980 by the Bent Crystal Spectrometer and the Hard X-ray Burst Spectrometer on the Solar Maximum Mission satellite. Results show that upward motions of the soft X-ray plasma are temporally associated with the build up of the thermal phase of flares and with the period of energy deposition as indicated by the hard X-ray emission. In addition, it is found that the hardness of the hard X-ray spectrum, the evaporation velocity, and the rate of increase of the gradual phase are correlated. It is also possible that the total electron energy deposited in the chromosphere, the peak emission measure of the evaporating plasma, and the peak emission measure of the thermal coronal plasma may also be correlated.

Antonucci, E.↗
NASA NTRS1983

On the probability of undetected error for the maximum distance separable codes

The performance of maximum-distance-separable codes with symbols from GF(1) when they are used for pure error detection or for simultaneous error correction and detection is investigated. These codes are good for symbol error detection. Their probability of undetected error is upper bounded by q to the -r and decreases monotonically as the symbol error probability epsilon decreases from (q-1)/q to 0, where r is the number of parity-check symbols of a code.

Kasami, T.↗
NASA NTRS1984

On the maximum-entropy/autoregressive modeling of time series

The autoregressive (AR) model of a random process is interpreted in the light of the Prony's relation which relates a complex conjugate pair of poles of the AR process in the z-plane (or the z domain) on the one hand, to the complex frequency of one complex harmonic function in the time domain on the other. Thus the AR model of a time series is one that models the time series as a linear combination of complex harmonic functions, which include pure sinusoids and real exponentials as special cases. An AR model is completely determined by its z-domain pole configuration. The maximum-entropy/autogressive (ME/AR) spectrum, defined on the unit circle of the z-plane (or the frequency domain), is nothing but a convenient, but ambiguous visual representation. It is asserted that the position and shape of a spectral peak is determined by the corresponding complex frequency, and the height of the spectral peak contains little information about the complex amplitude of the complex harmonic functions.

Chao, B. F.↗
NASA NTRS1984

An algorithm for maximum likelihood estimation using an efficient method for approximating sensitivities

An algorithm for maximum likelihood (ML) estimation is developed primarily for multivariable dynamic systems. The algorithm relies on a new optimization method referred to as a modified Newton-Raphson with estimated sensitivities (MNRES). The method determines sensitivities by using slope information from local surface approximations of each output variable in parameter space. The fitted surface allows sensitivity information to be updated at each iteration with a significant reduction in computational effort compared with integrating the analytically determined sensitivity equations or using a finite-difference method. Different surface-fitting methods are discussed and demonstrated. Aircraft estimation problems are solved by using both simulated and real-flight data to compare MNRES with commonly used methods; in these solutions MNRES is found to be equally accurate and substantially faster. MNRES eliminates the need to derive sensitivity equations, thus producing a more generally applicable algorithm.

Murphy, P. C.↗
NASA NTRS1972

Aerodynamic characteristics of 2 NASA supercritical airfoils with different maximum thickness

Transonic wind tunnel tests were conducted at Mach numbers from 0.60 to 0.81 to determine the aerodynamic characteristics of two NASA supercritical airfoils. The airfoils had maximum thicknesses of 10 and 11 percent of the chord. Normal forces and pitching moments acting on the airfoils were determined from surface static pressure measurements. Drag forces acting on the airfoils were derived from vertical variations of the total and static pressures measured across the wake. For the thinner airfoil, stall begins at approximately 0.1 higher normal-force coefficient at the higher test Mach numbers, and the drag divergence Mach number at a normal-force coefficient of 0.7 was 0.01 higher.

Harris, C. D.↗
NASA NTRS1984

Studies of solar magnetic fields during the solar maximum year

Observations and studies of solar magnetic fields that were carried out during the period of the solar maximum year (SMY) January 1980 to June 1981, are reviewed with the goal of providing a summary of what was learned about solar magnetic fields during the SMY. Such subjects as the relationship between solar magnetic fields and flares, the role of magnetic fields in the sunspot phenomenon, the magnetic-canopy structure overlying the supergranular network as well as the turbulent magnetic fields within the network, the fields within the polar crown prominences, and the solar magnetic cycle are addressed.

Hagyard, M. J.↗