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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 919 records · Page 51

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NASA NTRS1983

Fluid motions in the solar chromosphere-corona transition region. III - Active region flows from wide slit Dopplergrams

Large-scale velocity patterns observed in C IV in active regions show close correspondence with photospheric magnetic field patterns. In a large majority of cases, magnetic neutral lines show blueshift on their sun center side and redshift on their limbward side. The large-scale flow is consistent with widespread loop structure having downflow in both legs of the loops. Studies of individual bright loops, confirm that the flow is downward in most cases. However, an important subset of loops show flow from one end of the loop to the other.

Athay, R. G.↗

NASA NTRS1983

X-ray and microwave observations of active regions

Coordinated high-resolution (1-3 arcsec) observations of two active solar regions (H 421 and H 419) on November 16, 1979, are reported: soft-X-ray filtergrams from a sounding rocket flight, VLA total-intensity and circular-polarization microwave (6-cm) radio maps, KPNO full-disk photospheric magnetograms, and BBSO H-alpha data. The images were converted to 4.8-arcsec/mm-scale transparencies and coaligned on the basis of sunspot positions for comparison. The two active regions are characterized in detail, and intensity, size, and polarization data for the brightest microwave components (BMC) are listed. It is found that 19 of the 32 BMC are farther than 5 arcsec from any sunspot, and that X-ray-emitting structures only rarely correspond to sunspots, or BMC. About one third of the BMC are located at the feet or legs of coronal loops smaller than about 50,000 km. The limitations implied by these obervations for proposed thermal-bremsstrahlung, thermal-gyro-resonance, and nonthermal microwave-emission mechanisms are discussed.

Webb, D. F.↗

NASA NTRS1983

GSFC optical ozonesonde results during the Gap, France, intercomparisons, June 1981

O3 soundings made with balloon-borne optical sensors during the French Intercomparison Ozone Campaign in June, 1981, are reported. The GSFC four-channel UV-filter-photometer ozonesonde designed for the Super Loki rocket was attached to the gondola roof for redundant O3-density measurements at altitudes of 22-32 km, using the 300 and 303-nm filters. Sensor calibration, data processing, input constants, and vertical O3-distribution calculations are discussed. The density profiles for three legs of the flight, calculated using Bass or Vigroux cross sections, agreed within a standard error of 1.4 percent for each channel, but showed a consistent 4-5 percent (significant) difference between channels. Total average O3-column amounts determined by combining the GSFC data with ECC measurements for altitudes below 21 km were in good agreement with bias-corrected TOMS data from Nimbus-VII and with ground-based data from the Observatoire de Haute-Provence at Mt. Chiran, when the latter were computed using the pre-campaign calibration. A 9-percent discrepancy arose when the Chiran data were corrected for a post-campaign recalibration of the Dobson spectrophotometer.

Krueger, A. J.↗

NASA NTRS1983

Time controlled descent guidance algorithm for simulation of advanced ATC systems

Concepts and computer algorithms for generating time controlled four dimensional descent trajectories are described. The algorithms were implemented in the air traffic control simulator and used by experienced controllers in studies of advanced air traffic flow management procedures. A time controlled descent trajectory comprises a vector function of time, including position, altitude, and heading, that starts at the initial position of the aircraft and ends at touchdown. The trajectory provides a four dimensional reference path which will cause an aircraft tracking it to touchdown at a predetermined time with a minimum of fuel consumption. The problem of constructing such trajectories is divided into three subproblems involving synthesis of horizontal, vertical, and speed profiles. The horizontal profile is constructed as a sequence of turns and straight lines passing through a specified set of waypoints. The vertical profile consists of a sequence of level flight and constant descent angle segments defined by altitude waypoints. The speed profile is synthesized as a sequence of constant Mach number, constant indicated airspeed, and acceleration/deceleration legs. It is generated by integrating point mass differential equations of motion, which include the thrust and drag models of the aircraft.

Lee, H. Q.↗

NASA NTRS1983

Lower body graduated negative pressure system

The first task concerning the Lower Body Negative Pressure Suit was to determine the best type construction for a leg section with these goals in mind: good mobility, minimum amount of bulk, ease of storage, lightweight, rigid enough to withstand atmospheric pressure, and minimum amount of preparation before donning and donning time. After a study of three systems, wire hoops (rings) separated on inch apart in an airtight material furnished by NASA were chosen.

Source record↗

NASA NTRS1983

Modeling of transient disturbances in coronal-streamer configurations

Numerical simulations of the formation and propagation of mass ejection, loop transients in coronal streamers are discussed. The simulations are accomplished with numerical solutions of the single fluid, ideal MHD equations of motion in the meridional plane. The streamer is produced by simulating the relaxation of an initially radial hydrodynamic flow coupled with a dipole magnetic field. The simulated transient then results from an energy release at the base of the streamer. The legs of the loop transient produced remain essentially stationary while the loop expands mainly in the radial direction with velocities of 400 to 750 km s-1. Once the leading edge of the transient has passed out of the lower corona, the initial streamer configuration is restored after 15 to 24 hours. A second energy release 2 hours later than, and with an energy release identical to, the first does not produce a significant coronal disturbance.

Steinolfson, R. S.↗

NASA NTRS1984

Flow behavior in the Wright Brothers Facility

It has become increasingly apparent that a reexamination of the flow characteristics in the low speed Wright Brothers Facility (WBF) is of some importance in view of recent improvements in the precision of the data acquisition system. In particular, the existence of local regions of separation, if any, in back portions of the circuit, and possible related unsteadiness, are of interest. Observations from that initial experiment did indicate some unsteady air flow problems in the cross leg, and thereafter the test region (Section A) was calibrated quantitatively. The intent was to learn something about the effect of upstream intermittent behavior flow on the test section flow, as well as to provide an extensive calibration as a standard for the effects induced by future alteration of the tunnel. Distributions of total pressure coefficients were measured first at one cross-section plane of the test section, namely the model station. Data were obtained for several tunnel speeds. The reduced data yielded an unexpected distribution involving larger pressures along the inside wall.

Genn, S.↗

NASA NTRS1984

Engineering changes to the 0.1m cryogenic wind tunnel at Southampton University

The more important changes to the 0.1 m cryogenic wind tunnel since its completion in 1977 are outlined. These include detailed improvements in the fan drive to allow higher speeds, and the provision of a test section leg suitable for use with a magnetic suspension and balance system. The instrumentation, data logging, data reduction and tunnel controls were also improved and modernized. A tunnel performance summary is given.

Goodyer, M. J.↗

NASA NTRS1983

Redshifts of high-temperature emission lines in the far-ultraviolet spectra of late-type stars

High-dispersion IUE spectra of six late-type stars exhibit small but statistically significant differential redshifts of high-temperature emission lines, like Si IV and C IV, with respect to low-temperature lines like S I and O I. A well-exposed, small-aperture spectrum of the active chromosphere binary Capella (Alpha Aurigae A: G6 II+F9 III) establishes that the high-temperature lines are redshifted in an absolute sense with respect to the accurately determined photospheric velocity of the system at single-line phase 0.50. Several possible explanations for the stellar redshifts are discused, including a warm wind (100,000 K) in which aparent redshifts are produced in optically thick lines by an accelerating outfow, and the downflowing component of a vertical circulation system for which the up-leg portion of the flow is too cool, too hot, or too tenuous to be visible in Si IV and C IV. If the second scenario is true, the stellar redshifts may provide an important phenomenological link to the downflows observed in 100,000 K species over magnetic active regions in the sun.

Ayres, T. R.↗

NASA NTRS1984

Performance evaluation of the atmospheric phase of aeromaneuvering orbital transfer vehicles

Studies are underway to design reusable orbital transfer vehicles that would be used to transfer payloads from low-earth orbit to higher orbits and return. One promising concept is to use an atmospheric pass on the return leg to reduce the amount of fuel for the mission. This paper discusses a six-degree-of-freedom simulation analysis for two configurations, a low-lift-to-drag ratio configuration and a medium-lift-to-drag ratio configuration using both a predictive guidance technique and an adaptive guidance technique. Both guidance schemes were evaluated using the 1962 standard atmosphere and three atmospheres that had been derived from three entries of the Space Shuttle. The predictive technique requires less reaction control system activity for both configurations, but because of the limited number of updates and because each update used the 1962 standard atmosphere, the adaptive technique produces more accurate exit conditions.

Powell, R. W.↗

NASA NTRS1983

Dynamic behaviour of the K-corona above a type I radio source

Coronagraph images can be greatly enhanced by subtracting from the brightness of each picture point, the running median brightness over a square surrounding each picture point. The application of this technique to coronal analysis appears to be new. After such enhancement, images recorded by the SMM Coronagraph/Polarimeter reveal a coronal transient with previously undescribed characteristics. The transient began with bright ejecta moving up pre-existing rays and weaker, more diffuse, mass injection in the area between rays. At the sudden onset of this mass ejection the rays began to move apart from one another: during the ensuing 22 hr the separation of one pair of rays increased by 37 deg of latitude. Towards the end of the event these moving rays looked much like the legs of previously described loop transients. A type I radio source lay close to the center of symmetry of the transient.

Duncan, R. A.↗

NASA NTRS1984

Hy-wire measurements of atmospheric potential

A method for directly measuring the electric potential drop across the lowest portion of the atmosphere by using an apparatus called Hy-wire is described. The Hy-wire system consists of a long, high-voltage, insulated conductor connected at the top to a wire-mesh braid and terminated at the bottom inside a large-diameter corona ball mounted on 1 m Teflon legs. The system impedance is near 10 billion ohms, while the grounded mode, Hy-wire draws about 10 micro-a at 500 m altitude. Around-the-clock measurements with characteristic peaks near 1530 and 1900 UT of potentials near 125,000 volts are presented, with total daily average potential near 90,000 volts at 507 m altitude. The experimental weather conditions varied from clear to local fog, except that there was only trace precipitation. The data have been interpreted in terms of the possible source of the potential variations; neither a local nor a global source is clearly indicated.

Holzworth, R. H.↗

NASA NTRS1983

Cardiovascular responses to spaceflight

The cardiovascular system's adaptive changes during and after spaceflight are discussed. Cephalic fluid shifts are demonstrated by photographs along with calf girth and leg volume changes. Inflight measurements show an increase in average resting heart rate and systolic blood pressure, and a sympathetic-parasympathetic neural imbalance. Postflight findings include a small but reversible decrease in the left ventricular muscle mass. Since 1980, NASA's research has emphasized cardiovascular deconditioning and countermeasures: hemodynamic changes, endocrine and neurohumoral aspects, etiologic factors, and lower body negative pressure devices. Though human beings acclimate to the space environment, questions concerning the immediate and long-term aspects of spaceflight need to be answered for adequate planning of extended space missions.

Nicogossian, A.↗

NASA NTRS1984

The gamma-ray spectrum of Centaurus A - A high-resolution observation between 70 keV and 8 MeV

The NASA/Goddard Space Flight Center Low Energy Energy Gamma ray Spectrometer (LEGS) observed the nearby active nucleus galaxy Centaurus A (NGC 5128) during a balloon flight on 1981 November 19. There is no evidence of a break in the spectrum or of any line features. The 1.6 MeV limit is a factor of 8 lower than the 1974 line flux, indicating that, if the 1974 feature was real, and, if it was narrow, then the line intensity decreased significantly between 1974 and 1981. The lack of observed annihilation radiation from Cen A, combined with the temporal variations that are seen in the X-ray and gamma-ray intensities, constrain the size of the emission region to be between 10 to the 13th power and 5 x 10 to the 17th power cm. Previously announced in STAR as N83-35990

Gehrels, N.↗

NASA NTRS1984

Three-dimensional structures of two solar active regions from VLA observations at 2, 6, and 20 centimeter wavelengths

Three-dimensional structures of two active region groups are determined from observations with the Very Large Array (VLA) at 2, 6, and 20 cm. One of the groups exhibits a single magnetic loop of length approximately 10 to the 10th cm. The 2 cm radiation is mostly thermal bremsstrahlung and originates from the footprints of the loop. The 6 and 20 cm radiation is dominated by low-harmonic gyroresonance radiation and originates from the upper portion of the legs or the top of the loop. The loop broadens toward the apex. The top of the loop is not found to be the hottest point, but two temperature maxima on either side of the loop apex are observed, which is consistent with the model proposed for long loops. From 2 and 6 cm observations it can be concluded that the electron density and temperature cannot be uniform in a plane perpendicular to the axis of the loop; the density should decrease away from the axis of the loop.

Shevgaonkar, R. K.↗

NASA NTRS1986

Reduced-Stress Mounting for Thermocouples

Mounting accommodates widely different coefficients of thermal expansion. In new method, legs of thermocouple placed in separate n- and p-type arrays. Two arrays contact common heat pipe as source but have separate heatpipe sinks. Net expansion (or contraction) taken up by spring mounting on heat-pipe sinks.

Wood, C.↗

NASA NTRS1984

Mars exploration, Venus swingby and conjunction class mission modes, time period 2000 to 2045

Trajectory and mission requirement data are presented for Earth-Mars opposition class and conjunction class round trip stopover mission opportunities available during the time period year 2000 to year 2045. The opposition class mission employs the gravitational field of Venus to accelerate the space vehicle on either the outbound or inbound leg. The gravitational field of Venus was used to reduce the propulsion requirement associated with the opposition class mission. Representative space vehicle systems are sized to compare the initial mass required in low Earth orbit of one mission opportunity with another mission opportunity. The interplanetary space vehicle is made up of the spacecraft and the space vehicle acceleration system. The space vehicle acceleration system consists of three propulsion stages. The first propulsion stage performs the Earth escape maneuver; the second stage brakes the spacecraft and Earth braking stage into the Mars elliptical orbit and effects the escape maneuver from the Mars elliptical orbit. The third propulsion stage brakes the mission module into an elliptical orbit at Earth return. The interplanetary space vehicle was assumed to be assembled in and depart from the space station circular orbit.

Mars Exploration↗

NASA NTRS1985

Analytical modeling of circuit aerodynamics in the new NASA Lewis wind tunnel

Rehabilitation and extention of the capability of the altitude wind tunnel (AWT) was analyzed. The analytical modeling program involves the use of advanced axisymmetric and three dimensional viscous analyses to compute the flow through the various AWT components. Results for the analytical modeling of the high speed leg aerodynamics are presented; these include: an evaluation of the flow quality at the entrance to the test section, an investigation of the effects of test section bleed for different model blockages, and an examination of three dimensional effects in the diffuser due to reentry flow and due to the change in cross sectional shape of the exhaust scoop.

Towne, C. E.↗