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NASA NTRS1983

Simultaneous observation of rotational coherent Stokes Raman scattering and coherent anti-Stokes Raman scattering in air and nitrogen

Rotational coherent Stokes Raman scattering (CSRS) and coherent anti-Stokes Raman scattering (CARS) in air and in nitrogen were observed simultaneously by using broadband generation and detection. In the broadband technique used, the entire CARS and CSRS spectrum was generated in a single laser pulse; the CSRS and CARS signals were dispersed by a spectrograph and detected simultaneously by an optical multichannel analyzer. A three-dimensional phase-matching geometry was used to achieve spatial resolution of the CSRS and CARS beams from the input beams. Under resonant conditions, similar experiments may provide a means of investigating the possible interaction between the CSRS and CARS processes in driving the rotational levels.

Snow, J. B.↗

NASA NTRS1984

Simultaneous thermal vacuum testing of GPS drives for NavStar

The solar array drive assemblies for the global positioning satellite (GPS) were built and the need to perform thermal vacuum acceptance testing on at least two complete units simultaneously is emphasized. The safety of the flight hardware is of primary importance. It is found that simultaneous space simulation testing of two complete drive packages requires only minor modification to the high vacuum pump stack. Attention is given to upgrading system safeties for high vacuum operation. Major modifications are designed and implemented for the thermal control system and supporting subsystems. The automated thermal control system and test bed hardware are of primary interest.

Brown, T. G.↗

NASA NTRS1984

Distribution of aurora and ionospheric currents observed simultaneously on a global scale

The instantaneous spatial distribution of auroral emissions is observed with auroral imaging photometers on board the spacecraft Dynamics Explorer 1 (DE 1) as ground-based meridian chains of magnetometers simultaneously detect the magnetic signatures of ionospheric and field-aligned currents flowing at northern polar latitudes. Ionospheric conductivities at nighttime auroral latitudes are estimated from the measured auroral luminosities and used with the measured polar magnetic variations to compute model distributions of ionospheric and field-aligned currents. Temporal resolution for the coordinated observations and model calculations is 12 minutes. Model ionospheric and field-aligned current distributions are overlayed on global auroral images to illustrate spatial relations on a global scale at the maximum epoch of an auroral substorm. Eccentric-dipole-latitude and magnetic-local-time coordinates are used. A model field-aligned current distribution is compared quantitatively with the distribution of field-aligned currents inferred from simultaneous observations by the DE-2 magnetometer.

Craven, J. D.↗

NASA NTRS1984

Simultaneous ocean cross-section and rainfall measurements from space with a nadir-pointing radar

A method to determine simultaneously the rainfall rate and the normalized backscattering cross section of the surface was evaluated. The method is based on the mirror reflected power, p sub m which corresponds to the portion of the incident power scattered from the surface to the precipitation, intercepted by the precipitation, and again returned to the surface where it is scattered a final time back to the antenna. Two approximations are obtained for P sub m depending on whether the field of view at the surface is either much greater or much less than the height of the reflection layer. Since the dependence of P sub m on the backscattering cross section of the surface differs in the two cases, two algorithms are given by which the path averaged rain rate and normalized cross section are deduced. The detectability of P sub m, the relative strength of other contributions to the return power arriving simultaneous with P sub m, and the validity of the approximations used in deriving P sub m are discussed.

Meneghini, R.↗

NASA NTRS1985

Simultaneous Earth observations from 2 satellites

Simultaneous co-located observations from two different orbits lead to several advantages (i.e., cross calibration of sensors and a wider range of solar-zenith and sensor look angles). The question was asked how many times per year (on the average) do the sub-satellite points of two satellites simultaneously come within D kilometers of each other?. For the Space Station (altitude: 500 km, inclination: 28 deg) and a Sun synchronous satellite (altitude 705 km, inclination 98.21 deg) the answers are 16, 41 and 82 times per year for encounter distances D of 20, 50, and 100 km espectively. The relationship between encounters per year and distance D is linear. The answers were obtained in two ways: (1) a closed form statistical approach which led to a simple algebraic expression, and (2) a Monte Carlo type computer solution. The largest difference between the two solutions was less than 12%.

Montgomery, H. E.↗

NASA NTRS1986

Simultaneous fine structure observation of wind and temperature profiles by the Arecibo 430-MHz radar and in situ measurements

A simultaneous campaign of balloon and radar measurements took place on March 14 to 16, 1984, above the Arecibo 430-MHz radar. This radar was operating with a vertical resolution of 150 m following two antenna beam directions: 15 deg. from the zenith, respectively, in the N-S and E-W directions. The main results concerning the comparison between the flight and simultaneous radar measurements obtained on March 15, 1984 are analyzed. The radar return power profile (S/N ratio in dB) exhibits maxima which are generally well correlated with step-like structures in the potential temperature profile. These structures are generally considered as the consequence of the mixing processes induced by the turbulence. A good correlation appears in the altitude range 12.5 to 19 km between wind shears induced by a wave structure observed in the meridional wind and the radar echo power maxima. This wave structure is characterized by a vertical wavelength of about 2.5 km, and a period in the range 30 to 40 hours. These characteristics are deduced from the twice daily rawinsonde data launched from the San Juan Airport by the National Weather Service. These results pointed out an example of the interaction between wave and turbulence in the upper troposphere and lower stratosphere. Turbulent layers are observed at locations where wind shears related to an internal inertia-gravity wave are maxima.

Thomas, D.↗

NASA NTRS1986

Simultaneous earth observations from two satellites

Simultaneous co-located observations from two different orbits lead to several advantages (i.e., cross calibration of sensors and a wider range of solar-zenith and sensor look angles). The question was asked how many times per year (on the average) do the sub-satellite points of two satellites simultaneously come within D kilometers of each other? For the Space Station (altitude: 500 km, inclination: 28 deg) and a Sun synchronous satellite (altitude 705 km, inclination 98.21 deg) the answers are 16, 41 and 82 times per year for encounter distances D of 20, 50, and 100 km respectively. The relationship between encounters per year and distance D is linear. The answers were obtained in two ways: (1) a closed form statistical approach which led to a simple algebraic expression, and (2) a Monte Carlo type computer solution. The largest difference between the two solutions was less than 12 percent.

Montgomery, H. E.↗

NASA NTRS1987

Simultaneous structure/control optimization of large flexible spacecraft

This paper presents an approach to the simultaneous optimal design of a structure and control system for large flexible spacecrafts based on realistic objective function and constraints. The weight or total cost of structure and control system is minimized subject to constraints on the magnitude of response to a given disturbance involving both rigid-body and elastic modes. A nested optimization technique is developed to solve the combined problem. As an example, simple beam-like spacecraft under a steady-state white-noise disturbance force is investigated and some results of optimization are presented. In the numerical examples, the stiffness distribution, the location of controller and the control gains are optimized. Direct feedback control and linear quadratic optimal control laws are used with both inertial and non-inertial disturbing force. It is shown that the total cost is sensitive to the overall structural stiffness so that a simultaneous optimization of the structure and control system is indeed useful.

Onoda, Junjiro↗

NASA NTRS1986

Transverse auroral ion energization observed on DE-1 with simultaneous plasma wave and ion composition measurements

Simultaneous high-time-resolution plasma-wave and ion-composition measurements obtained with DE-1 during a magnetospheric-cusp crossing on March 15, 1984 and during an evening auroral-zone crossing on January 4, 1984 are reported. The data are presented graphically and characterized in detail, with a focus on the transverse energization of H(+) and O(+) ions. An O(+) distribution observed during the cusp crossing is shown to be well represented by a bi-Maxwellian distribution with temperatures 180 eV parallel and 250 eV perpendicular to the local magnetic field and a bulk flow velocity of 27 km/s up the magnetic-field line. In the auroral-zone data a simultaneous transverse-energy increase is detected in both H(+) and O(+) components in the presence of plasma-wave emissions at multiples of the hydrogen gyrofrequency.

Peterson, W. K.↗

NASA NTRS1987

Simultaneous multifrequency observations of Markarian 421

Simultaneous radio, optical, ultraviolet, and X-ray observations of the highly variable BL Lacertae object Mrk 421 conducted over a period of four days in December 1984 and again in January 1985 are reported. During this time, the 2-10 keV flux dropped by a factor of eight, whereas the 0.1-1 keV flux decreased by a factor of only two. These changes were not reproduced at longer wavelengths during the period of simultaneous observation. The implications of these results for beaming models, the relation between BL Lacertae objects and other classes of AGN, and the nature of the core regions of active galaxies are discussed.

Brodie, Jean↗

NASA NTRS1987

An approach to structure/control simultaneous optimization for large flexible spacecraft

This paper presents an approach to the simultaneous optimal design of a structure and control system for large flexible spacecrafts based on realistic objective function and constraints. The weight or total cost of structure and control system is minimized subject to constraints on the magnitude of response to a given disturbance involving both rigid-body and elastic modes. A nested optimization technique is developed to solve the combined problem. As an example, simple beam-like spacecraft under a steady-state white-noise disturbance force is investigated and some results of optimization are presented. In the numerical examples, the stiffness distribution, location of controller, and control gains are optimized. Direct feedback control and linear quadratic optimal controls laws are used with both inertial and noninertial disturbing force. It is shown that the total cost is sensitive to the overall structural stiffness, so that simultaneous optimization of the structure and control system is indeed useful.

Onoda, Junjiro↗

NASA NTRS1987

Simultaneous observation of Pc 3-4 pulsations in the solar wind and in the earth's magnetosphere

The equatorially orbiting Active Magnetospheric Particle Tracer Explorers CCE and IRM satellites have made numerous observations of Pc 3-4 magnetic field pulsations (10-s to 100-s period) simultaneously at locations upstream of the earth's bow shock and inside the magnetosphere. These observations show solar wind/IMF control of two categories of dayside magnetospheric pulsations. Harmonically structured, azimuthally polarized pulsations are commonly observed from L = 4 to 9 in association with upstream waves. More monochromatic compressional pulsations are clearly evident on occasion, with periods identical to those observed simultaneously in the solar wind. The observations reported here are consistent with a high-latitude (cusp) entry mechanism for wave energy related to harmonically structured pulsations.

Engebretson, M. J.↗

NASA NTRS1987

Simultaneous sampling technique for two spectral sources

A technique is described that uses a bundle of fiber optics to simultaneously sample a dye laser and a spectral lamp. By the use of a real-time display with this technique, the two signals can be superimposed, and the effect of any spectral adjustments can be immediately accessed. In the NASA's CARS system used for combustion diagnostics, the dye laser mixes with a simultaneously pulsed Nd:YAG laser at 532 nm to probe the vibrational levels of nitrogen. An illustration of the oscilloscopic display of the system is presented.

Jarrett, Olin, Jr.↗

NASA NTRS1987

Simultaneous measurements of energetic ion (50 keV and above) and electron (220 keV and above) activity upstream of earth's bow shock and inside the plasma sheet - Magnetospheric source for the November 3 and December 3, 1977 upstream events

Simultaneous observations of energetic ions and electrons by the IMP 7 and 8 spacecraft are used here to separate temporal variations from spatial variations during the upstream ion events observed on December 3, 1977 and November 2-3, 1977, in order to determine the source of these particles. Analysis of the observations and comparison with theory shows that: (1) for each of the observed upstream enhancements, energetic ions and electrons were simultaneously present inside the plasma sheet; (2) the low-energy ion intensity profile inside the plasma sheet was relatively flat, while at higher energies there was considrable variability; (3) relativistic electron bursts were seen inside the plasma sheet and also upstream of the shock but at substantially reduced intensities; (4) the ion energy spectrum for the December 3 event, extended to energies of about 2 MeV, was identical in form with the plasma sheet and upstream of the shock; (5) ion anisotropies exhibited typically large dawn-dusk or dusk-dawn gradients and large field-aligned streaming away from the bow shock.

Sarris, E. T.↗

NASA NTRS1988

Simultaneous Exosat and VLA observations of the contact binaries VW Cephei and XY Leonis - Quiescent emission and a flare on VW Cephei

Two W UMa-type contact binaries, XY Leo and VW Cep, were observed simultaneously with Exosat, the VLA, and, in the case of XY Leo, optically. The temporal coverage of each star was sufficient to monitor them throughout two orbital revolutions (P about 0.27 days); however, no orbital modulation of either the X-ray or 6 cm data was seen for either star, indicating large emitting regions. A large flare from VW Cep was detected, the best such simultaneous flare data ever obtained from a star other than the sun. Its behavior before, during, and after the flare was remarkably similar to that found in solar flares, although at 6 cm this flare on VW Cep was about 10,000 times more luminous than typical strong solar flares. For both stars, it is demonstrated that the 6 cm emission cannot be the result of bremsstrahlung radiation of the X-ray emitting plasma; in fact, it is shown, in the case of the VW Cep flare, that the 6 cm emission is consistent with gyrosynchrotron radiation from a source region of order of the system separation.

Vilhu, Osmi↗

NASA NTRS1988

Simultaneous Exosat and VLA observations of the W UMa binaries, VW Cep and XY Leo - A flare on VW Cep

Two UMa-type contact binaries, XY Leo and VW Cep, have been observed simultaneously with Exosat, the VLA, and, in the case of XY Leo, optically. The temporal coverage of each star was sufficient to monitor them throughout two orbital revolutions (P about 0.25 days), however, no orbital modulation of either the X-ray or 6-cm data was seen for either star. A large flare from VW Cep was detected, the first such simultaneous flare ever seen on a star other than the sun. Its behavior before, during, and after the flare is remarkably similar to that found in solar flares. For both stars, it is demonstrated that the 6-cm emission cannot be the result of bremsstrahlung radiation of the X-ray emitting plasma.

Vilhu, Osmi↗

NASA NTRS1990

The ionosphere as a focusing lens - A case study involving simultaneous type III solar radio storm measurements from the ISIS 1 and 2 and ISEE 3 satellites

The possibility of using terrestrial ionospheric focusing to improve the directivity of electric dipoles on space missions has been investigated by comparing simultaneous observations of a solar radio storm by the ISIS 1 and ISIS 2 spacecraft, in near earth orbit, and the ISEE 3 spacecraft located beyond the magnetosphere. To this end, a three-dimensional ray tracing in a spherically stratified ionosphere has been carried out for conditions appropriate to the observations by the ISIS spacecraft of a solar radio storm in September 1983. The procedure allows Poynting flux spectral densities measured on ISIS to be converted to spectral densities well outside the ionosphere where they can be compared directly with simultaneous observations on ISEE 3. The results demonstrate good agreement over their common observing frequency range (1-2 MHz).

James, H. G.↗

NASA NTRS1990

Simultaneous, in situ measurements of OH and HO2 in the stratosphere

Stratospheric OH and HO2 radical densities have been measured between 36 and 23 km using a balloon-borne, in situ instrument launched from Palestine, Texas on August 25, 1989. OH is detected using the laser-induced fluorescence technique (LIF) employing a Cu-vapor-laser pumped dye laser coupled with an enclosed-flow detection chamber. HO2 is detected nearly simultaneously by adding NO to the sample flow to convert ambient HO2 to OH. Observed OH and HO2 densities ranged from 8.0 + or - 2.8 x 10 to the 6th and 1.4 + or - 0.5 x 10 to the 7th molec/cu cm, respectively, at 36 km, to 1.4 + or - 0.5 x 10 to the 6th and 3.0 + or - 1.0 x 10 to the 6th at 23 km, where the uncertainty is + or - sigma. The HO2 density exhibits a maximum in the 34-30 km region of 1.7 + or - 0.6 x 10 to the 7th. The data were obtained over a solar zenith angle variation of 51 deg at 36 km to 61 deg at 23 km. O3 and H2O densitites also were measured simultaneously with separate instruments.

Stimpfle, R. M.↗