SEARCH · Search NASA

Results for “background”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 451 records · Page 25

All sources NASA NTRS DOE OSTI

NASA NTRS1989

Test chamber for low-background IR focal plane testing

A unique and versatile vacuum chamber has been designed for JPL's IR Focal Plane Technology Group. This chamber is equipped with multiple ports for cryogen and electrical vacuum feedthroughs, pumping units, vacuum gages, sources, and detector camera heads. The design incorporates a liquid-nitrogen-cooled optical table and radiation shield for low-background IR detector testing. Focal planes can be tested at temperatures ranging from 300 K to that of liquid helium. This paper describes the design and construction of this low-background IR focal plane test chamber and discusses some of its distinctive features. An analysis of the test chamber's performance is also presented.

Staller, Craig↗

NASA NTRS1990

A procedure for the extraction of airglow features in the presence of strong background radiation

A technique is developed that can be used to derive the total intensity of band emissions from twilight airglow measurements when the basic spectral signature of the band to be considered is known. The method is designed to automatically extract total band or line intensities of a signal imbedded in background radiation several orders of magnitude greater in brightness. It is shown that the technique developed can reliably measure the intensity of both weak and strong band and line emissions in the presence of strong twilight background radiation. The method of extraction is shown as part of a general purpose spectral analysis program written in VAX FORTRAN. This extraction procedure has been used successfully on emissions of Fel, Ca(+), N2(+) (1N) (0-0) and (0-1), OH in the near UV. OI red (630nm) and green (558nm) lines in the visible, and the OH Meinel bands and O(+) (2P) 732 nm in the near IR.

Swift, W. R.↗

NASA NTRS1990

LWIR detector requirements for low-background space applications

Detection of cold bodies (200 to 300 K) against space backgrounds has many important applications, both military and non-military. The detector performance and design characteristics required to support low-background applications are discussed, with particular emphasis on those characteristics required for space surveillance. The status of existing detector technologies under active development for these applications is also discussed. In order to play a role in future systems, new, potentially competing detector technologies such as multiple quantum well detectors must not only meet system-derived requirements, but also offer distinct performance or other advantages over these incumbent technologies.

Deluccia, Frank J.↗

NASA NTRS1990

A new approach to remove interorder background in high dispersion IUE images

A two dimensional Chebyshev interpolating scheme, followed by modeling of point spread functions as Voigt profiles, is proposed for final archiving IUESIPS to remove the interorder overlap from the smoothed background fluxes of high dispersion International Ultraviolet Explorer (IUE) images. Tests of the first and last stages of the algorithm suggest that it can give a considerably better zero point than the old IUESIPS algorithm which samples local interorder background.

Smith, Myron A.↗

NASA NTRS1990

Contamination control program for the Cosmic Background Explorer: An overview

Each of the three state of the art instruments flown aboard NASA's Cosmic Background Explorer (COBE) were designed, fabricated, and integrated using unique contamination control procedures to ensure accurate characterization of the diffuse radiation in the universe. The most stringent surface level cleanliness specifications ever attempted by NASA were required by the Diffuse Infrared Background Experiment (DRIBE) which is located inside a liquid helium cooled dewar along with the Far Infrared Absolute Spectrophotometer (FIRAS). The DRIBE instrument required complex stray radiation suppression that defined a cold primary optical baffle system surface cleanliness level of 100A. The cleanliness levels of the cryogenic FIRAS instrument and the Differential Microwave Radiometer (DMR) which were positioned symmetrically around the dewar were less stringent ranging from 300 to 500A. To achieve these instrument cleanliness levels, the entire flight spacecraft was maintained at level 500A throughout each phase of development. The COBE contamination control program is described along with the difficulties experienced in maintaining the cleanliness quality of personnel and flight hardware throughout instrument assembly.

Barney, Richard D.↗

NASA NTRS1990

Early results from the Cosmic Background Explorer (COBE)

The Cosmic Background Explorer, launched 18 Nov. 1989, has nearly completed its first full mapping of the sky with all three of its instruments: A Far Infrared Absolute Spectrometer (FIRAS) covering 0.1 to 10 mm, a set of Differential Microwave Radiometers (DMR) operating at 3.3, 5.7, and 9.6 mm, and a diffuse Infrared Background Experiment (DIRBE) spanning 1 to 300 microns in ten bands. A preliminary map of the sky derived from DIRBE data is presented. Initial cosmological implications include: a limit on the comptonization parameter of 0.001, on the chemical potential parameter of 0.01, a strong limit on the existence of a hot smooth intergalactic medium, and a confirmation that the dipole anisotropy has the spectrum expected from a Doppler shift of a blackbody. There are no significant anisotropies in the microwave sky detected, other than from our own galaxy and a cos theta dipole anisotropy whose amplitude and direction agree with previous data. At shorter wavelengths, the sky spectrum and anisotropies are dominated by emission from local sources of emission within our Galaxy and Solar System. Preliminary comparison of IRAS (Infrared Astronomical Satellite) and DRIBE sky brightnesses toward the ecliptic poles shows the IRAS values to be significantly higher than found by DRIBE at 100 microns. The presence of gain and zero point errors in the IRAS total brightness data is suggested. The spacecraft, instrument designs, and data reduction methods are described.

Mather, J. C.↗

NASA NTRS1989

Background stratospheric aerosol reference model

In this analysis, a reference background stratospheric aerosol optical model is developed based on the nearly global SAGE 1 satellite observations in the non-volcanic period from March 1979 to February 1980. Zonally averaged profiles of the 1.0 micron aerosol extinction for the tropics and the mid- and high-altitudes for both hemispheres are obtained and presented in graphical and tabulated form for the different seasons. In addition, analytic expressions for these seasonal global zonal means, as well as the yearly global mean, are determined according to a third order polynomial fit to the vertical profile data set. This proposed background stratospheric aerosol model can be useful in modeling studies of stratospheric aerosols and for simulations of atmospheric radiative transfer and radiance calculations in atmospheric remote sensing.

Mccormick, M. P.↗

NASA NTRS1991

Non-Gaussian microwave background fluctuations from nonlinear gravitational effects

Whether the statistics of primordial fluctuations for structure formation are Gaussian or otherwise may be determined if the Cosmic Background Explorer (COBE) Satellite makes a detection of the cosmic microwave-background temperature anisotropy delta T(sub CMB)/T(sub CMB). Non-Gaussian fluctuations may be generated in the chaotic inflationary model if two scalar fields interact nonlinearly with gravity. Theoretical contour maps are calculated for the resulting Sachs-Wolfe temperature fluctuations at large angular scales (greater than 3 degrees). In the long-wavelength approximation, one can confidently determine the nonlinear evolution of quantum noise with gravity during the inflationary epoch because: (1) different spatial points are no longer in causal contact; and (2) quantum gravity corrections are typically small-- it is sufficient to model the system using classical random fields. If the potential for two scalar fields V(phi sub 1, phi sub 2) possesses a sharp feature, then non-Gaussian fluctuations may arise. An explicit model is given where cold spots in delta T(sub CMB)/T(sub CMB) maps are suppressed as compared to the Gaussian case. The fluctuations are essentially scale-invariant.

Salopek, D. S.↗

NASA NTRS1990

A dipole moment of the microwave background as a cosmological effect

A spherically symmetrical Tolman-Bondi cosmological model is presented in which the curvature of space and the entropy variety with distance from the center. The dipole and quadrupole moments in the distribution of the microwave background radiation are calculated as a function of cosmic time and position of an observer, assuming that the distance to the horizon is much smaller than any characteristic scale in the model. The quadrupole moment is found to be affected mostly by the gradient in the curvature of space while the dipole moment is dominated by the gradient of entropy. The results indicate that the observed dipole in the microwave background may be cosmological in origin. Observational tests of this argument are suggested.

Paczynski, Bohdan↗

NASA NTRS1991

Cosmic X-ray background from hot gas

This paper considers constraints on models of the cosmic X-ray background (XRB) in which the XRB is produced by optically thin thermal bremsstrahlung from hot gas. It is shown that models in which the gas is gravitationally confined in a spherical configuration and is heated only once are contradicted by the observed number of gravitationally lensed quasars together with the lower limit on the number of XRB sources required by limits on fluctuations in the XRB and the cosmic microwave background. In addition, it is shown that, for models in which the gas is not gravitationally confined, the expansion time of the gas is much shorter than the radiative cooling time, so that such models cannot explain the XRB. It is concluded that thermal bremsstrahlung models cannot account for the XRB if the emitting gas is heated only once.

Rogers, R. D.↗

NASA NTRS1991

Thermal design of the Cosmic Background Explorer cryogenic optical assembly

The Cosmic Background Explorer (COBE) is a satellite which is designed to study the 3-K cosmic background radiation. Two cryogenic instruments and a common support structure comprise the Cryogenic Optical Assembly (COA). In order to make definitive measurements of the low-energy FIR radiation, the temperature of the COA must be maintained below 3 K. Temperature control of the COA elements is achieved by the use of a superfluid helium dewar. The thermal design also minimizes power dissipation, transient operational effects, and thermal gradients within the COA. This is accomplished by isolating selected components and heat-sinking others to various locations on the cryogen tank. The thermal design was developed primarily through analysis. Analytical models were created to perform parametric design studies. Ground testing was performed to correlate the thermal models and validate the thermal design. Both test and flight data confirmed that all design requirements were either met or exceeded.

Mosier, Carol L.↗

NASA NTRS1989

Infrared-fiber-optic fire sensor developments - Role of measurement uncertainty in evaluation of background limited range

Fire-detector systems based on distributed infrared fiber-sensors have been investigated for potential applications in the aerospace industry. Responsivities to blackbody and flame radiations were measured with various design configurations of an infrared fiber-optic sensor. Signal processing techniques were also investigated, and the results show significant differences in the fire-sensor performance depending on the design configuration. Measurement uncertainties were used to determine the background-limited ranges for the various fire-sensor concepts, and the probability of producing false alarms caused by fluctuations in the background signals were determined using extreme probability theory. The results of the research show that infrared fiber-optic fire sensors are feasible for application on manned spacecraft; however, additional development work will be required to eliminate false alarms caused by high temperature objects such as incandescent lamps.

Tapphorn, Ralph M.↗

NASA NTRS1991

Cosmic backgrounds from primeval dust

A general formalism is developed for describing the spectrum and the anisotropy of radiation from primeval dust as a nearly isotropic cosmic background with fluctuations. The theory incorporates spatial and temporal variations in the density of both luminosity and dust and is sufficiently robust to treat emission by point sources, as well as smoother emission, in high and low optical depth situations. The fluctuations are calculated using linear perturbation theory for arbitrary dust and luminosity clumping, and are calculated nonperturbatively for compact IR sources using shot-noise models. For many realistic models, a large accompanying NIR background is predicted. It is shown that, while spectal information alone provides only coarse information about the dust abundance and type, the redshift, and the other parameters, it may provide a powerful probe of pregalactic history when used in combination with the anisotropy signal.

Bond, J. R.↗

NASA NTRS1991

What COBE might see - The far-infrared cosmological background

The redshifted emission from infrared luminous galaxies should produce a diffuse background around 300 microns detectable by the Cosmic Background Explorer (COBE). The detection of such emission would provide evidence for evolution in the density or luminosity of galaxies in the infrared.

Beichman, C. A.↗

NASA NTRS1990

The soft X-ray background and its origins

A review on the soft X-ray background is presented, with emphasis on diffuse galactic emission. Particular attention is given to emission mechanisms for the galactic diffuse background, the observational data, models of the 0.5-1 keV and of the 70-284 eV emission, and limits on the extragalactic flux.

Mccammon, Dan↗

NASA NTRS1991

Spectral observations of the extreme ultraviolet background

The design of a grazing incidence spectrometer for measuring the diffusive extreme-ultraviolet astronomical background radiation is outlined, and the data obtained on the diffusive background between 80 and 650 A is discussed. The strongest emission line detected is solar backscattered He I 584 A radiation; solar 304 A radiation resonantly scattered by geocoronal He II is observed in both first and second order; and each of three remaining spectral features is found to be consistent with those expected from hot interstellar gas. Of these features, the strongest is the feature at 635 A identified as 630 A O v emission. A feature centered at about 99 A is fitted by a cluster of Fe XVIII and Fe XIX lines from gas at log T = 6.6-6.8, and a feature discovered near 178 A is found to be consistent with Fe X and Fe XI emission from gas at log T = 6.

Labov, Simon E.↗

NASA NTRS1991

Contamination control program for the Cosmic Background Explorer

Barney, Richard D.↗

NASA NTRS1991

Small-scale fluctuations of the X-ray background

Fluctuations of the diffuse X-ray background are investigated using the Einstein Observatory Deep Survey data. Small angular-scale variations of the numbers of counts in the energy range 0.8-3.5 keV in the central 32 x 32 sq arcmin of the IPC are analyzed by means of the two-point correlation function. It is shown that detector modulation contributes substantially to the observed fluctuations. Instrumental effects are estimated and subtracted from the raw observations. The residual fluctuations are used to estimate the log N-log S relation of the X-ray sources below the Einstein sensitivity limit. Taking into account numerous uncertainties involved in this analysis, it is shown that the amplitude of fluctuations observed in the Deep Survey data is consistent with a relatively small number of sources producing the X-ray background.

Soltan, A. M.↗