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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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NASA NTRS2021

Pyrolysis Rate and Yield Strength Reduction Incarbon Fiber and Glass Fiber Composites Underreentry Heating Conditions

The behavior of composite materials, specifically carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP), under reentry conditions poses a problem for space debris reentry risk modeling. Since these materials pyrolyze rather than melt and their different components demise at different rates, modeling their destruction to determine ground impact risk is complex. Modern spacecraft are using these materials in ever-greater quantities owing to their superior strength-to-weight characteristics, and this has required that the orbital debris community improve its understanding of how these materials demise on reentry. The NASA Orbital Debris Program Office undertook an extensive test campaign to better understand the rate at which several types of GFRP and CFRP materials pyrolyze under reentry heating conditions and how that pyrolysis affects the ultimate strength of the material. GFRP with a polyester resin (G10/FR-4) and CFRP with epoxy, cyanate ester, vinyl ester, and phenolic resins were tested. The test campaign was carried out at the Inductively Coupled Plasma (ICP) Torch Facility at the University of Texas at Austin. Because the ICP facility operates in a shirt-sleeve environment, test samples can be changed within seconds or minutes, allowing many samples to be tested in a short period. Two heat flux rates, 20 W/m2 and 30W/m2, and two oxygen concentration conditions, 0% and 2% of atmospheric, were applied to all five types of material. To measure both the char rate and the effect of pyrolysis on the ultimate material strength, two types of test were carried out for each material: a char rate test on a ~10 mm thick sample of material and an in-situ bending stress test of a ~2 mm thick sample of material. Measurements of the char rate showed very similar average pyrolysis front velocity in epoxy resin CFRP as in G10 at 3.6 mm/min and 3.4 mm/min, respectively. However, the total mass loss rate in theG10 was nearly double that of the CFRP at 3.8 g/min and 2.2 g/min, respectively. This result represented a slow ablation rate of carbon fibers in the CFRP at the temperatures encountered in low Earth orbit reentry and a comparatively rapid removal of the glass fibers in G10 due to melting and spallation. Pyrolysis front velocity was more significantly affected by the type of plastic than the type of fiber, with the cyanate ester CFRP samples displaying an average pyrolysis front velocity of only 1.9 mm/min. Similarly, the effect of thermal exposure on the ultimate strength of the material depended heavily on the type of plastic and very little on the type of fiber in the material. Epoxy, vinyl ester, and polyester resins all behaved very similarly, with complete structural failure at between 400 J/g and 600 J/g of specific absorbed heat. Phenolic and cyanate ester resins, on the other hand, displayed a change in structural properties that was only barely measurable with the current apparatus even after the maximum exposure time tested. These data are being incorporated into a numerical model of the ablation and demise of composite materials that will be used to more accurately calculate the ground casualty risk of future spacecraft.

Benton R. Greene↗
NASA NTRS1984

On the bizarre gamma-ray spectrum of SS 433

Lamb et al. (1983) have announced the discovery of a pair of gamma-ray lines interpretable as emission of the 1.368 MeV line of Mg-24 in the two oppositely directed relativistic jets of SS 433. The mass loss rate related to the Mg-24 and the kinetic energy flux of the Mg-24 are considered. In the present investigation, it is shown that the mass loss flux must be well in excess of 0.00001 solar mass per yr, while the abundance of the gamma-emitting nucleus is extremely high. Attention is given to the calculation of the gamma-ray production efficiency factor, the size of the emitting region, reaction processes, and X-ray luminosity. It is concluded that for plasma beam models, there must be a substantial overabundance, by a factor of 100 to approximately 1000, of the gamma-line producing nucleus. The association of the gamma-ray lines with Mg-24 is reasonable but not secure.

Helfer, H. L.↗
NASA NTRS1987

Space Infrared Telescope Facility (SIRTF) design and thermal analysis

The design and performance characteristics of an observatory are compared with those of a storage dewar. The critical design technologies required to increase cryogen dewar lifetime are discussed. In particular, outer shell temperature, vapor cooled shields, multilayer insulation performance, and tank support systems are analyzed to assess their impact on cryogen lifetime for both the observatory and the storage dewar. The cryogen lifetime and cryogen mass loss rate of the Space Infrared Telescope Facility (SIRTF) are compared with that of the Infrared Astronomy Satellite and the Cosmic Background Explorer Satellite. A 0.1 percent mass loss per day of superfluid helium dewar can be designed using current state-of-the-art dewar technology. Space-based liquid hydrogen and liquid oxygen tanks can be designed for a 5-year lifetime.

Lee, Jeffrey H.↗
NASA NTRS1993

Escape of Mars atmospheric carbon through time by photochemical means

Luhmann et al. recently suggested that sputtering of the Martian atmosphere by re-entering O(+) pickup ions could have provided a significant route of escape for CO2 and its products throughout Mars' history. They estimated that the equivalent of C in an approximately 140-mbar CO2 atmosphere should have been lost this way if the Sun and solar wind evolved according to available models. Another source of escaping C (and O) that is potentially important is the dissociative recombination of ionospheric CO(+) near the exobase. We have evaluated the loss rates due to this process for 'ancient' solar EUV radiation fluxes of 1, 3, and 6 times the present flux in order to calculate the possible cumulative loss over the last 3.5 Gyr.

Luhmann, J. G.↗
NASA NTRS1972

Inhibition of the ablation rate of graphite by gaseous chlorine.

Investigation of the inhibiting effect of gaseous chlorine on the ablation rate of graphite. It is shown that small amounts of chlorine gas, when present in a supersonic high-temperature air environment, can inhibit the ablation rate of graphite and depress its surface temperature below that measured in pure air. The ablation inhibition performance of chlorine is presented in graphs in terms of mass loss rate and surface temperature depression as a function of chlorine concentration.

Maahs, H. G.↗
NASA NTRS1986

Mass return to the interstellar medium from highly-evolved carbon stars

Data produced by the Infrared Astronomy Satellite (IRAS) was surveyed at the mid- and far-infrared wavelengths. Visually-identified carbon stars in the 12/25/60 micron color-color diagram were plotted, along with the location of a number of mass-losing stars that lie near the location of the carbon stars, but are not carbon rich. The final sample consisted of 619 objects, which were estimated to be contaminated by 7 % noncarbon-rich objects. The mass return rate was estimated for all evolved circumstellar envelopes. The IRAS Point Source Catalog (PSC) was also searched for the entire class of stars with excess emission. Mass-loss rates, lifetimes, and birthrates for evolved stars were also estimated.

Latter, W. B.↗
NASA NTRS1999

High-Altitude Aircraft and Balloon-Borne Observations of OH, HO2, ClO, BrO, NO2, ClONO2, ClOOCl, H2O, and O3 in Earth's Stratosphere

Using observations from balloon-borne instruments and aircraft-borne instruments the investigation arrived at the following developments.: (1) Determination of the dominant catalytic cycles that destroy ozone in the lower stratosphere; (2) The partial derivatives of the rate limiting steps are observables in the lower stratosphere; (3) Recognition that the "Low NOx" condition is the regime that holds the greatest potential for misjudgement of Ozone loss rates; (4) Mapping of the Bromine radical contribution to the ozone destruction rate in the lower stratosphere; (5) Observation of OH, HO2 and ClO in the plume of the Concorde SST in the stratosphere; (6) Determination of the diurnal behavior of OH in the lower stratosphere; (7) Observed OH and H02 in the Troposphere and the interrelationship between Ozone and OH, HO2, CO and NO; (8) Analysis of the Catalytic Production of Ozone and Reactions that Couple OH and H02 in the Troposphere; (9) The continuing development of the understanding of the Tropopause temperatures, water vapor mixing ratios, and vertical advection and the mixing in of mid-latitude air; (10) Performed Multiple Tracer Analyses as a diagnostic of water vapor intrusion into the "Middle World" (i.e., the lowermost stratsophere); (11) Flight testing of a new instrument for the In Situ detection of ClON02 from the ER-2; (12) Laser induced fluorescence detection of NO2. There is included an in depth discussion of each of these developments and observations.

Anderson, James G.↗
NASA NTRS1982

Prediction of corridor effect from the launching of the satellite power system

A diagnostic model is developed to define the parameters which control the corridor effect of contaminants deposited in a narrow latitudinal band of the earth's atmosphere by numerous launches of the STS and heavy lift launch vehicles for construction of satellite solar power systems. Identified factors included the pollution injection rate, the ambient background levels of the pollutant species, and the transport properties related to the dilution rate of the chemicals. If the chemical life of the pollutant was shorter or the same length of time as the transport time, alterations in the chemical production and loss rates were found to be parameters necessarily added to the model. A comparison with NASA Ames Research Center two-dimensional model results indicate that the corridor effect was possile with operations above 60 km in the case of H2O, H2, and NO production.

Borucki, W. J.↗
NASA NTRS1986

RV Tauri stars as post-asymptotic giant branch objects

RV Tau stars are rare, luminous pulsators of spectral types F, G, and K. Analysis of the IRAS data shows that the mass-loss rates from RV Tau stars have apparently significantly decreased during the past 500 yr. It seems likely that these stars have just evolved from the phase of rapid mass loss, characteristic of the last stages of the asymptotic giant branch (AGB). The birthrate of RV Tau stars in the solar neighborhood is about a tenth of the birthrate of all planetary nebulae, and this is consistent with the view that we are witnessing the subset of stars undergoing post-AGB evolution that are low mass and at least in some cases of low metallicity.

Jura, M.↗
NASA NTRS1977

The influence of autoionization accompanied by excitation on dielectronic recombination and ionization equilibrium

In the process of dielectronic recombination, the doubly excited state formed by radiationless capture may autoionize preferentially into an excited state of the recombining ion. This additional autoionization process has not been discussed in previous treatments of dielectronic recombination. The dielectronic recombination rates for certain nonhydrogenic Fe ions, although still larger than the direct radiative recombination rates, are found to be substantially reduced by the inclusion of the additional autoionization rate in the branching ratio for the stabilizing radiative transition. Consequently, the temperatures of maximum equilibrium abundance are significantly lower than those predicted by recent calculations. Finally, the radiative energy loss rate coefficients are calculated for radiation processes involving electron Fe-ion collisions in high-temperature plasmas. Electron impact excitation of resonance line radiation is the dominant radiative cooling mechanism in steady-state plasmas at temperatures where ions with bound electrons are abundant. However, it is found that the radiation emitted during dielectronic recombination can be more important than direct recombination radiation and bremsstrahlung.

Jacobs, V. L.↗
NASA NTRS1971

Kinetic limitations on the diffusional control theory of the ablation rate of carbon.

It is shown that the theoretical maximum oxidation rate is limited in many cases even at temperatures much higher than 1650 deg K, not by oxygen transport, but by the kinetics of the carbon-oxygen reaction itself. Mass-loss rates have been calculated at air pressures of 0.01 atm, 1 atm, and 100 atm. It is found that at high temperatures the rate of the oxidation reaction is much slower than has generally been assumed on the basis of a simple linear extrapolation of Scala's 'fast' and 'slow' rate expressions. Accordingly it cannot be assumed that a transport limitation inevitably must be reached at high temperatures.

Maahs, H. G.↗
NASA NTRS1981

Graphitic heat shields for solar probe missions

The feasibility of using a graphitic heat-shield system on a solar probe going to within 4 solar radii of the center of the sun is investigated. An analysis of graphite vaporization, with commonly used vaporization coefficients, indicates that the maximum mass-loss rate from a conical shield as large as 4 m in diameter can be kept low enough to avoid interference with measurements of the solar environment. In addition to the mass-loss problem, the problem of protecting the payload from the high-temperature (up to 2300 K) primary shield must be solved. An analysis of radiation exchange between concentric disks provides a technique for designing the intermediate shielding. The technique is applied to the design of a system for the Starprobe spacecraft, and it is found that a system with 10 shields and a payload surface temperature of 600 K will have a payload diameter of 2.45 m. Since this is 61% of the 4-m diameter of the primary shield, it is concluded that a graphitic heat-shield system is feasible for the Starprobe mission.

Lundell, J. H.↗
NASA NTRS1981

New insight into the physics of atmospheres of early type stars

The phenomenon of mass loss and stellar winds from hot stars are discussed. The mass loss rate of early type stars increases by about a factor of 100 to 1000 during their evolution. This seems incompatible with the radiation driven wind models and may require another explanation for the mass loss from early type stars. The winds of early type stars are strongly variable and the stars may go through active phases. Eclipses in binary systems by the stellar winds can be used to probe the winds. A few future IUE studies are suggested.

Lamers, H. J. G. L. M.↗
NASA NTRS1981

Shock waves, atmospheric structure and mass loss in Miras

Large amplitude shock waves are observed to be present in the atmospheres of the Mira variables: spectral line doubling with Delta v 30 km/s is present in infrared spectra. Even the visible spectra contain some evidence for such shocks. These shocks are sufficiently large to clearly dominate the energy balance of the atmosphere. Mira variables also show symptoms of substantial mass loss rates: they are strong maser and infrared continuum sources and have strong circumstellar absorption features. The pulsation induced shocks which are seen to be present are obvious suspects for causing or enhancing the mass loss from these stars. The Miras thus present an ideal case for the study of dynamical effects on atmospheric structure, since both the dynamics and the results are clearly observable. The results are given of calculations of the thermalization and cooling of the shock heated material passing through shock fronts whose properties were selected to be consistent with both the isothermal models and the spectroscopic observations.

Willson, L. A.↗
NASA NTRS1983

Ultraviolet spectroscopic observations of some Be stars of later type and A-F type shell stars

High-dispersion IUE spectra of 18 later type Be and A-F type shell stars as well as eight standard nonemission line stars have been analyzed for anomalous ionization and mass loss effects. It is found that superionization in the Be stars extends to the latest spectral subtypes but does not seem to be present in the A-F type stars. The superionized lines in the Be stars appear to be correlated with v sin i. Asymmetrical or violet-displaced resonance lines suggesting mass loss are observed in all the Be stars except one, in some of the standard stars, but not in the A-F stars. Lower limits to the mass loss rates computed from Si IV lines range between 5.3 x 10 to the -12th and 3.5 x 10 to the -11th solar masses/yr, with Be shell stars showing the largest values. Mass loss is correlated with luminosity and effective temperature but not with rotation.

Carpenter, K. G.↗
NASA NTRS1992

Evolutionary impact of sputtering of the Martian atmosphere by O(+) pickup ions

Calculations of solar wind-induced loss rates for evolving solar and atmospheric conditions like those described by Zhang et al. (1992), but including sputtering of the Martian atmosphere by reentering O(+) pickup ions, are described. The inclusion of the sputter loss increases by about 30 percent the cumulative estimated loss of oxygen to that in about 50 m of water (global surface depth) over the last 3.5 billion years. These ions also sputter CO2 and its fragments in substantial amounts. That integrated loss is equivalent to about 0.14 bar atmospheric CO2 pressure, of the order of some estimates of Mars' early atmospheric inventory.

Luhmann, J. G.↗
NASA NTRS1994

First measurement of helium on Mars: Implications for the problem of radiogenic gases on the terrestrial planets

The 108 photons of the Martian He 584 A airglow detected by the Extreme Ultraviolet Explorer satellite during a two-day exposure (22-23 Jan. 1993) correspond to the effective disk average intensity of 43 (+/-) 10 Rayleigh. Radiative transfer calculations, using a model atmosphere appropriate to the conditions of the observation and having an exospheric temperature of 210 (+/-) 20 K, result in an He mixing ratio of 1.1 (+/-) 0.4 ppm in the lower atmosphere. Nonthermal escape of helium is due to the following: electron impact ionization and pickup of He(+) by the solar wind; collisions with hot oxygen atoms; and charge exchange with molecular species with corresponding column loss rates of 1.4 x 10(exp 5), 3 x 10(exp 4), and 7 x 10(exp 3) cm(exp -2)s(exp -1), respectively. The lifetime of helium on Mars is 5 x 10(exp 4) yr. The He outgassing rate, coupled with the Ar-40 atmospheric abundance and with the K:U:Th ratio measured in the surface rocks, is used as input to a simple two-reservoir degassing model which presumes the loss of all argon accumulated in the atmosphere during the first Byr by large-scale impacts. The model results in total planet mass ratios of 10(exp -5) g/g for K, 2.3 x 10(exp -9) g/g for U, 8.5 x 10(exp -9) g/g for Th, 4 x 10(exp -10) g/g for He, and 1.5 x 10(exp -9) g/g for Ar-40. The predicted radiogenic heat flux is 2 erg cm(exp -2)s(exp -1). Similar modeling for Venus results in total plant mass ratios of 4.7 x 10(exp -5) g/g for K, 6.7 x 10(exp -9) g/g for U, 2.2 x 10(exp -8) g/g for Th, 1.3 x 10(exp -9) for He, 6.7 x 10(exp -9) g/g for Ar-40, and a radiogenic heat flux of 15 erg cm(exp -2)s(exp -1). The implications of these results are discussed. The modeling shows that the radioactive elements were not distributed uniformly in the protoplanetary nebula, and their relative abundances differ very much in the terrestrial planets.

Bowyer, S.↗