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At least 235 records · Page 13

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NASA NTRS1984

The STEP/STACBEAM experiment technology development for very large solar array deployers

The Stacking Triangular Articulated Compact Beam (STACBEAM) is discussed with reference to structural testing experiments afforded by ground simulation and the Space Technology Experiments Platform (STEP). The STACBEAM lends itself to a deployment technique which offers a radical improvement in flexible blanket solar array technology. A system for deployment and support of a solar array blanket is described which consists of the blanket, its containment structure, the support structure and its deployer, the blanket stiffening battens, and the deployable boom standoffs. In operation, the blanket is pulled out and supported by the STACBEAM which packages next to the folded blanket. Since the STACBEAM does not rotate during extension, complete control of the blanket is maintained during extension. Deployment of this system occurs one bay at a time in a sequential manner. The deployer provides sufficient rigidity so that beam stiffness is not degraded during the deployment process.

Samuels, R.↗

NASA NTRS1983

Stagnation-point ablation of carbonaceous flat disks. II Experiment

Six flat-disk models made of carbon-carbon and carbon-phenolic materials were launched in an argon-filled track-range facility to test ablation characteristics in a radiation-dominated, massive-blowing environment. The shock standoff distances deduced from the shadowgraphs agree with theoretical predictions during the earlier portion of the flight, while the wall temperatures determined by the image-converter photographs agree with predictions during the later portion. The measured surface recessions exceed the calculated values by about 60 percent for carbon-phenolic and 30 percent for carbon-carbon. The discrepancies are attributed to spallation. The measured char thicknesses agree with theoretical predictions.

Park, C.↗

NASA NTRS1984

Analytical characterization of AOTV perigee aerothermodynamic regime

In preliminary design studies of AOTV (Aeroassisted Orbital Transfer Vehicle) configurations, it is desirable to have a simple analytical method for characterizing the aerothermodynamic regime at skip trajectory perigee as a function of vehicle L/D and m/CDA (ballistic coefficient). The present study derives an approximate perigee solution from the generalized equations of motion. For a prescribed entry velocity vector, the solution determines a Zeta function (proportional to density divided by m/CDA) at perigee as a parametric function of the exit velocity vector and (constant) L/D. The perigee Zeta function then determines perigee density (or altitude) as a parametric function of m/CDA. The solution allows the following classic aerothermodynamic parameters to be determined at perigee as parametric functions of m/CDA, L/D, and the exit velocity vector: Reynolds Number (viscous effects), Mach Number (compressibility effects), Knudsen Number (rarefaction effects), sphere and disk bow shock standoff distance, Damkohler Number (relaxation effects), viscous correlation parameter (viscid-inviscid interactions), and Stanton Number (convective heat transfer). Results of the analysis are given for low L/D and mid L/D AOTV configurations on return from geosynchronous and L5 orbits. It is concluded the method successfully provides preliminary estimates of the aerothermodynamic parameters through the use of simple algebraic equations and plots.

Desautel, D.↗

NASA NTRS1985

Blind-Side, High-Temperature Fastener Lock

Formed-in-place staple provides positive mechanical lock. Post-supported, advanced carbon/carbon standoff panels, currently under consideration as alternate thermal protection system for Shuttle orbiter, locking feature applicable to temperatures of 1,600 degrees F (870 degrees C) and higher and employable after panel installed, resulting in blind application. Blind-side locking technique employs wire staple inserted into grooves in post, formed in place by ramped portion of post grooves. This splays out wire ends that move into castellated end of grommet, mechanically locking post and grommet against relative rotation. Splayed ends provide mechanical lock to prevent wire from falling out.

Matza, E. C.↗

NASA NTRS1985

Solar wind flow about the outer planets - Gas dynamic modeling of the Jupiter and Saturn bow shocks

It has been found that the solar wind is diverted about planets through the formation of bow shocks which heat and deflect the flow. These observations are based on missions concerned with Mercury, Venus, earth, and Mars during the 1960s and 1970s. The present study has the objective to extend to Jupiter and Saturn certain aspects of the analyses which have been carried out on the terrestrial planets. In particular, the Pioneer 10 and 11 and Voyager 1 and 2 observations near Jupiter and Saturn are used to characterize the relevant upstream flow parameters at 5 and 9 AU. Attention is given to solar wind parameters, bow shock and magnetopause models, and the solar wind standoff distance, and aspects of gas-dynamic modeling.

Slavin, J. A.↗

NASA NTRS1985

The shuttle glow: A program to study the ram-induced phenomena

In January 1984, a proposal was submitted to NASA Headquarters entitled The Shuttle Glow: A Program to Determine the Physics of the Ram induced Phenomena. This proposal included the following elements in a shuttlebased experiment: (1) The use of a special flat generating surface 1 x 3 m on which the glow can be produced and observed. This surface will be maneuvered to vary the orientation of ram flow and of projected component of geomagnetic field. (2) Remotely mounted optical instruments to view the glowing layer on the plate. By scanning, the variation of radiance as a function of wavelength and standoff distance from the plate will be observed looking parallel to the plate. (3) The preferred location of the generating plate and in situ diagnostics is on the end of the Remote Manipulator System (RMS) arm.

Anderson, H. R.↗

NASA NTRS1985

A computer-assisted process for supersonic aircraft conceptual design

Design methodology was developed and existing major computer codes were selected to carry out the conceptual design of supersonic aircraft. A computer-assisted design process resulted from linking the codes together in a logical manner to implement the design methodology. The process does not perform the conceptual design of a supersonic aircraft but it does provide the designer with increased flexibility, especially in geometry generation and manipulation. Use of the computer-assisted process for the conceptual design of an advanced technology Mach 3.5 interceptor showed the principal benefit of the process to be the ability to use a computerized geometry generator and then directly convert the geometry between formats used in the geometry code and the aerodynamics codes. Results from the interceptor study showed that a Mach 3.5 standoff interceptor with a 1000 nautical-mile mission radius and a payload of eight Phoenix missiles appears to be feasible with the advanced technologies considered. A sensitivity study showed that technologies affecting the empty weight and propulsion system would be critical in the final configuration characteristics with aerodynamics having a lesser effect for small perturbations around the baseline.

Johnson, V. S.↗

NASA NTRS1986

Heat flux observations and the location of the transition region boundary of Giacobini-Zinner

Electron heat flux observations and associated plasma phenomena upstream from Comet Giacobini-Zinner show many similarities to observations upstream from the earth's magnetosheath. Two similarities are discussed. Heat flux events are used to compute the transition region boundary location. The computed subsolar standoff distance of 4,000 km is commensurate with a comet gas production rate, G, of 3 x 10 to the 28th molecules/s in accord with ground-based determination of G.

Fuselier, S. A.↗

NASA NTRS1986

Heating distribution comparison between asymmetric and symmetric blunt cones

An experiment was performed to compare the heating distribution between symmetric and asymmetric large-angle blunt cones, with cone angles of 100, 120, and 140 deg. These hot-wall data were obtained from models made from typical thermal protection insulation for proposed aeroassisted orbital transfer vehicles. Experimental data are compared with predictions using a boundary-layer integral matrix procedure with kinetics to determine how well the heating distribution over an asymmetric cone could be approximated using axisymmetric solutions for a cone and spherical segment. In addition, a relationship between the stagnation-point heat-transfer rate and the bow-shock standoff distance for these cones is discussed. The heat-distribution data from the symmetric and asymmetric cones were very similar. Numerical results compared well with the measured wall temperatures at the stagnation point but slightly underpredicted them over the conical portion of the models.

Stewart, D. A.↗

NASA NTRS1986

Direct simulation of typical AOTV entry flows

The direct simulation Monte Carlo method is applied to two flows that are relevant to the projected aeroassisted orbital transfer vehicle. The first is the axially symmetric flow about a 70 degree blunted cone shield with a cylindrical afterbody, and the second is the one-dimensional flow along the stagnation streamline of the first flow. The shock standoff distance for the stagnation streamline study is obtained from the full axially symmetric calculation. Advantage is then taken of the speed of the one-dimensional calculation to study the sensitivity of the stagnation point heat transfer to a number of physical variables. These include the chemical reaction rate coefficients, the surface catalycity, the electric field associated with ambipolar diffusion, and the nonequilibrium thermal radiation from the shock front.

Bird, G. A.↗

NASA NTRS1986

Effects of variables upon pyrotechnically induced shock response spectra

Throughout the aerospace industry, large variations of 50 percent (6 dB) or more are continually noted for linear shaped charge (LSC) generated shock response spectra (SRS) from flight data (from the exact same location on different flights) and from plate tests (side by side measurements on the same test). A research program was developed to investigate causes of these large SRS variations. A series of ball drop calibration tests to verify calibration of accelerometers and a series of plate tests to investigate charge and assembly variables were performed. The resulting data were analyzed to determine if and to what degree manufacturing and assembly variables, distance from the shock source, data acquisition instrumentation, and shock energy propagation affect the SRS. LSC variables consisted of coreload, standoff, and apex angle. The assembly variable was the torque on the LSC holder. Other variables were distance from source of accelerometers, accelerometer mounting methods, and joint effects. Results indicated that LSC variables did not affect SRS as long as the plate was severed. Accelerometers mounted on mounting blocks showed significantly lower levels above 5000 Hz. Lap joints did not affect SRS levels. The test plate was mounted in an almost free-free state; therefore, distance from the source did not affect the SRS. Several varieties and brands of accelerometers were used, and all but one demonstrated very large variations in SRS.

Smith, J. L.↗

NASA NTRS1986

Self indexing latch system

A self-latching jaw assembly is described which includes a pair of jaws for latching a fitting of an associated structure such as the keel fitting of a space telescope. The jaw assembly automatically locates the fitting received on a positioning pedestal and latches it in its original location on the pedestal without need of precision alignment. The first jaw is actuated and moved to the right whereupon a reciprocating plunger, extended from the nose of the jaw senses the hub of the spool. A jaw position responsive switch is then actuated to terminate the drive motor of the jaw. The astronaut will then actuate the drive motor of the jaw and the jaw will move to the left, whereupon the standoff will engage the face of the jaw in a latching position. In the latching position, the noses of the jaws will be under the flanges of the spool.

John C Gibson↗

NASA NTRS1987

Coaxial tube array space transmission line characterization

The coaxial tube array tether/transmission line used to connect an SP-100 nuclear power system to the space station was characterized over the range of reactor-to-platform separation distances of 1 to 10 km. Characterization was done with respect to array performance, physical dimensions and masses. Using a fixed design procedure, a family of designs was generated for the same power level (300 kWe), power loss (1.5 percent), and meteoroid survival probability (99.5 percent over 10 yr). To differentiate between vacuum insulated and gas insulated lines, two different maximum values of the E field were considered: 20 kV/cm (appropriate to vacuum insulation) and 50 kV/cm (compressed SF6). Core conductor, tube, bumper, standoff, spacer and bumper support dimensions, and masses were also calculated. The results of the characterization show mainly how transmission line size and mass scale with reactor-to-platform separation distance.

Switzer, Colleen A.↗

NASA NTRS1987

Nonequilibrium radiation during re-entry at 10 km/s

The direct simulation Monte Carlo method, including a real air model with thermal radiation, is applied to the flows associated with the two sets of measurements that are directly relevant to the projected aeroassisted orbital transfer vehicle. The first is a shock tube measurement of the radiation from a 10 km/s shock wave in air that was made at AVCO in 1962. The second is the flight data that was obtained from the Project Fire re-entry test vehicles in 1964. The calculations for both cases were made with a program that models the one-dimensional flow along a stagnation streamline. The shock standoff distance for the Fire vehicle was obtained from the theoretical studies that were associated with its launch. The simulation employed a partly phenomenological model for the nonequilibrium radiation. It was found that the results from the calculation were consistent with the measured radiation in each case, and also with the convective heat transfer data for the Fire vehicle. The uncertainties associated with the spectral absorptance and recombination probability at the surface appear to be as serious as those associated with the reaction rates.

Bird, G. A.↗

NASA NTRS1987

Characteristics of the Marslike limit of the Venus-solar wind interaction

The response of the Venus ionosphere to the solar wind when the latter exceeds the peak thermal pressure in the Venus ionosphere is characterized on the basis of observations from the Pioneer Venus Orbiter. At these times, the Venus ionosphere becomes increasingly magnetized until the total ionospheric pressure matches that of the solar wind. The ionopause becomes less distinct and asymptotically approaches a limiting altitude of about 220 km for extremely high pressures. When the ionopause is low, the hot regions of electrons which occurs within the ionopause gradient extends to lower altitudes. The ion temperatures show little change, and there is no discernible increase in plasma wave activity at the ionopause. The Venus observations at high dynamic pressure provide a framework for reassessing the available Mars observations. In particular, this study shows that solar wind standoff without sufficient ionospheric plasma pressure cannot by itself be used as evidence for a planetary magnetic field.

Luhmann, J. G.↗

NASA NTRS1988

Heating Distributions For Aeroassisted Vehicles

Report discusses anticipated distributions of temperature on symmetric and asymmetric large-angle blunt nose-cone space vehicles re-entering atmosphere. Report considers three cone angles; 100 degree, 120 degree, and 140 degree. Experimental surface-temperature data obtained on specimens made of thermal-protection materials proposed for vehicles. Discusses relationship between stagnation-point heat-transfer rate and bow-shock standoff distance for cones.

Stewart, David A.↗

NASA NTRS1987

Tool and process for miniature explosive joining of tubes

A tool and process to be used in the explosive joining of tubes is disclosed. The tool consists of an initiator, a tool form, and a ribbon explosive. The assembled tool is a compact, storable, and safe device suitable for explosive joining of small, lightweight tubes down to 0.20 inch in diameter. The invention is inserted into either another tube or a tube plate. A shim or standoff between the two surfaces to be welded is necessary. Initiation of the explosive inside the tube results in a high velocity, angular collision between the mating surfaces. This collision creates surface melts and collision bonding wherein electron-sharing linkups are formed.

Bement, Laurence J.↗

NASA NTRS1987

Coaxial tube array space transmission line characterization

Switzer, Colleen A.↗