Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “RE”

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.

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

At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1961

ANALYSIS OF QUARTZ AND TEFLON SHIELDS FOR A PARTICULAR RE-ENTRY MISSION

The transient performance of ablation type heat protection shields is treated herein for the surface of a vehicle returning from outer space to the earth. The vehicle weighs 8640 kg, has a ballistic factor of 500 lb/ft2, re-enters with a speed of 11 km/sec at 120 km altitude, has a lift over drag ratio of -0.5, and is subjected to a maximum deceleration of 7.7 times the gravity constant. By use of well-known equations for the heat transfer and the mass transfer at a heated surface, a numerical calculation method is derived which, for the investigated ablation processes, yields exact transient solutions of the fundamental system of partial differential equations. The method is applied to various quartz shields and to one Teflon shield, which all evaporate so readily under the conditions of the problem at hand that practically no flow of molten shield material exists. The solutions also show comparatively small temperature changes parallel to the surface. The results show that the nose of the vehicle is cooled predominantly by the evaporation of the quartz or the Teflon; the rest of the vehicle's surface is cooled by radiation of the quartz or evaporation of the Teflon. The large mass transfer effects on the nose of the vehicle are detrimental since the resulting low surface temperatures prevent the radiative heat transfer out of the shield, which does not involve any mass loss, from being the desirable governing cooling factor.

ABLATING MATERIAL↗
NASA NTRS1968

Propulsive re-entry aerodynamics Interim report, 1 Jun. 1967 - 1 Jun. 1968

This report discusses the progress accomplished during the first year of a two-year contract to study Propulsive Re-Entry Aerodynamics. Analytical methods were developed during the first year to predict the flow field in the immediate vicinity of a planetary entry system composed of an aeroshell with a single retrorocket which exhausts into a subsonic or supersonic counterflowing planetary atmosphere. In the second year a digital computer program will be developed for the analytical solutions, and the analytical model will be tested by performing an experimental test program and comparing the experimental results with the analytical predictions. The analytical investigation considers the flow field due to a single supersonic retrorocket exhausting from an aeroshell into oncoming subsonic, transonic, or supersonic streams in the large thrusting coefficient regime, 0.5 < C(sub T) = T/q(sub ∞) A(sub m) < 15, which is the range of thrusting coefficients encountered during the terminal landing phase for planetary landing on Mars or Venus. Analyses are provided for all the geometrical features of the flow field such as the location of the terminal shock, jet boundary, and the profile for the interface between the jet and atmospheric gases. In addition, analyses are developed which describe the growth of the mixing layers along the interface and at the edge of the jet boundary and dead-air region and the reattachment of the shear layer to the aeroshell or the recompression of the shear layer in wake type flow. A comprehensive discussion of the experimental wind tunnel test program to be accomplished in Phase II is presented.

Philip O Jarvinen↗
NASA NTRS1972

Superconductivity in thin films of the Mo-Re system.

A series of Mo-Re alloy films has been prepared by sputtering from a composite molybdenum and rhenium cathode. These films were deposited in an ultra-high purity environment onto sapphire substrates which were held at temperatures ranging from 400 to 1300 C. Maximum transition temperatures observed were 15 K which is significantly greater than the highest reported bulk values. Critical current and field characteristics also were found to be considerably greater in the films compared to corresponding bulk samples. Upper critical fields of over 100 kOe were measured. These enhanced properties are discussed in relation to the structural characteristics of the sputtered films.

Gavaler, J. R.↗
NASA NTRS1972

Measured drift of irradiated and unirradiated W3%Re/W25%Re thermocouples at a nominal 2000 K.

Seven tantalum sheathed, BeO insulated, 0.157-cm-diam, grounded-junction W-3%Re/W-25%Re thermocouples were irradiated in a helium-argon environment at a temperature of 1900 to 2100 K. Six other thermocouples from the same lot were operated out-of-pile with the same temperature history as the in-pile thermocouples. Drift-in-pile was determined by periodically replacing a 'reference' thermocouple in the irradiation capsule. Drift out-of-pile was determined with an optical pyrometer. After 8000 hours irradiation, the estimated neutron fluence was 4 x 10 to the 21st power thermal neutrons/sq cm and 0.9 x 10 to the 21st power fast neutrons/sq cm (E greater than 0.18 MeV). At this time the in-pile group had decreased in output the equivalent of 340 K at 2073 K, while the out-of-pile group had decreased in output the equivalent of 54 K at 2073 K. The maximum deviation in drift between thermocouples of the in-pile group and between thermocouples of the out-of-pile group was less than plus or minus 15 K and less than plus or minus 10 K, respectively.

Heckelman, J. D.↗
NASA NTRS1974

Influence of ablation impurities on blunt body re-entry ionization

Electron density profiles which include the effect of an ablated sodium impurity were computed for the boundary layer on a blunt-nosed body re-entering the atmosphere at 7.62 km/sec. Profiles are computed from the nose to a distance of four diameters along the RAM C-payload. A finite-difference, laminar, nonequilibrium chemistry boundary-layer program was used. Comparison of theory with S-band diagnostic antenna results, electron concentration deduced from X- and C-band attenuation data, and Langmuir probe data at several different aft body locations show that agreement is good at high altitude. At the lower altitudes there is disagreement between theory and S-band antenna data where the apparent discrepancy is attributed to the three-body recombination rate constant used for deionization of sodium coupled with the effect of angle of attack.

Schexnayder, C. J., Jr.↗
NASA NTRS1975

Feasibility and process scale-up low cost alumina fibers for advanced Re-usable Surface Insulation (RSI)

The objective of this program was to establish feasibility of a process to produce low cost aluminum oxide fibers having sufficient strength, flexibility, and thermal stability for multiple re-use at temperatures to 1480 C in advanced RSI type heat shields for reentry vehicles. Using bench-scale processing apparatus, the Alcoa 'Saphiber' process was successfully modified to produce nominally 8 microns diameter polycrystalline alpha-alumina fiber. Thermal stability was demonstrated in vacuum reheating tests to 1371 C and in atmospheric reheating to 1483 C. Individual fiber properties of strength, modulus, and flexibility were not determined because of friability and short length of the fiber. Rigidized tile produced from fiber of nominally 8, 20 and 40 micron diameter had thermal conductivities significantly higher than those of RSI SiO2 or mullite at relatively low temperature but became comparable above about 1000 C. Tile densities were high due to short fiber length, especially in the coarser diameter fiber. No significant effect of fiber diameter on thermal properties could be determined form the data. Mechanical properties of tiles deteriorated as fiber diameter increased.

Pearson, A.↗
NASA NTRS1977

Re-entrant groove heat pipe

This paper describes theoretical and experimentally verified heat pipe characteristics of an axially grooved aluminum extrusion with a re-entrant groove profile. The extrusion is 13 mm diameter with 20 axial grooves, each groove consisting of a nominal .8 mm diameter channel with a .2 mm wide passageway connecting the channel to the hollow core. A computer program was written to compute the zero gravity heat transport capability of the extrusion. A heat pipe was fabricated and its performance characteristics measured. The characteristics of the pipe with ammonia at 20 C are: zero gravity pumping limit 143 w-meters; static wicking height 21.5 mm; evaporator and condenser coefficients 7300 and 20,500 watt/sq m C, respectively.

Harwell, W.↗
NASA NTRS1977

Ablative performance of carbon-carbon nosetips in simulated re-entry environments

A summary is presented of ablation performance data for carbon-carbon nosetip models obtained over a range of pressures from 10 to 168 atm. Two classes of tests are reviewed: (1) steady state, in which a constant environment is imposed on the model, and (2) ramp, in which the pressure is increased from 10 to 80 atmospheres to simulate re-entry pressure history. Comparison of arc test parameters with typical reentry vehicle parameters is included, to assess the adequacy of the test simulation. Based on this comparison, recommendations are made for facility developments which would yield improved simulation capability for reentry vehicle nosetip ablative performance.

Nestler, D. E.↗
NASA NTRS1981

Fixed-trim re-entry guidance analysis

The terminal guidance problem for a fixed-trim re-entry body is formulated with the objective of synthesizing a closed-loop steering law. A transformation of variables and subsequent linearization of the motion, with the sight-line to the target as a reference, reduces the order of the state system for the guidance problem. The reduced order system, although nonlinear and time-varying, is simple enough to lend itself to synthesis of a class of guidance laws. A generalization of the feedforward device of classical control theory is successfully employed for compensation of roll autopilot lags. The proposed steering law exhibits superior miss-distance performance in a computational comparison with existing fixed-trim guidance laws.

Gracey, C.↗