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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Significance of DSMC Computed Aerothermal Environments in the Rarefied Regime for Atmospheric Entry Material Response

During Mars atmospheric entry, the Mars Science Laboratory (MSL) was protected by a 4.5 meters diameter ablative heatshield assembled in 113 tiles. The heatshield was made of NASA's flagship ablative material, the Phenolic Impregnated Carbon Ablator (PICA). Prior work compared the traditional one-dimensional and three-dimensional material response models at different locations in the heatshield. It was observed that the flow was basically one-dimensional in the nose and flank regions, but three-dimensional flow effects were observed in the outer flank. The objective of this work is to study the effects of the aerothermal environment on the material response. We extend prior work by computing aerothermal environments using the direct simulation Monte Carlo (DSMC) code SPARTA and the CFD code Data Parallel Line Relaxation (DPLR). SPARTA is used to compute environment in the rarefied regime prior to 48.4s of entry where the Knudsen number is such that the Navier-Stokes equations can be inaccurate. Similarly to previous work, the DPLR software is used to compute the hypersonic environment for laminar then turbulent boundary layer assumptions from 48.4 s up to 100 s after Entry Interface (EI) along the MSL 08-TPS-02/01a trajectory. We observe that extending the aerothermal environments to times prior to 48.4 s modifies the thermal response of the heat shield at the surface and in-depth; however the effects on the recession are minimal. Additionally, using the assumption of a turbulent boundary layer versus a laminar one leads to higher surface and in-depth temperatures, larger recession, and a displacement of the peak heating and peak recession location.

Aerothermal↗
NASA NTRS1987

Atmospheric entry heating of cosmic dust

A computer simulation of the atmospheric entry deceleration and heating for micrometeorites into a planetary atmosphere was developed. The results of this model were compared to an earlier model. The major difference between the extent of heating experienced in the two models results from an underestimation of the atmospheric density at altitudes above 130 km in the earlier model. Thus the earlier model systematically overestimates the peak temperature reached on atmospheric entry. The discrepancies are small for near vertical entry and/or high density particles, where little deceleration is experienced at high altitudes. For particles entering at grazing incidence and/or of low density the discrepancies are more pronounced. Gravitational enhancement, which is a function of geocentric velocity at the collection opportunity, was found to bias near Earth cosmic dust collections in favor of low velocity particles. The effect is to increase the proportion of low velocity dust, predominately from asteroids, in the stratospheric cosmic dust collections and on Earth orbiting spacecraft impact surfaces over its proportion in the interplanetary dust cloud.

Flynn, George J.↗
NASA NTRS1997

Guidance and Control for Mars Atmospheric Entry: Adaptivity and Robustness

In this paper, we address the atmospheric entry guidance and control problem for Mars precision landing. The guidance and control design is based on the principle of tracking a reference drag versus velocity profile in the entry flight corridor, which is determined by physical constraints of the flight. An integrated adaptive/robust control approach to atmospheric entry guidance and control is introduced to deal with different uncertainties.

Lu, Wei-Min↗
NASA NTRS2017

Titan Atmospheric Entry Radiative Heating

Detailed spectrally and spatially resolved radiance has been measured in the Electric Arc Shock Tube for conditions relevant to Titan entry, varying atmospheric composition, free-stream density (equivalent to altitude) and shock velocity. Permutations in atmospheric composition include 1.1, 2, 5 and 8.6 CH4 by mole with a balance of N2 and 1.5 CH4 0.5 Ar 98 N2 by mole, which is consistent with the current understanding of Titan's atmosphere. The effect of gas impurities identified in previous shock tube studies were also examined by testing in pure N2 and deliberate addition of air to the CH4N2 mixtures. The test campaign measured radiation at velocities from 4.7 kms to 8 kms and free-stream pressures from 0.1 to 0.47 Torr. These conditions cover a range of potential trajectories for flight missions, including a direct ballistic trajectory, a fly by or an extremely high speed entry. Radiances measured in this work are substantially larger compared to that reported both in past EAST test campaigns and other shock tube facilities. Depending on the metric used for comparison, the discrepancy can be as high as an order of magnitude. Potential causes for the discrepancy, such as the effect of oxygen due to Air leakage, gas composition and purity are discussed. The present work provides a new benchmark set of data to replace those published in previous studies.

Earth↗
NASA NTRS2017

Titan Atmospheric Entry Radiative Heating

Detailed spectrally and spatially resolved radiance has been measured in the Electric Arc Shock Tube for conditions relevant to Titan entry, varying atmospheric composition, free-stream density (equivalent to altitude) and shock velocity. Permutations in atmospheric composition include 1.1, 2, 5 and 8.6 CH4 by mole with a balance of N2 and 1.5 CH4 0.5 Ar 98 N2 by mole, which is consistent with the current understanding of Titan's atmosphere. The effect of gas impurities identified in previous shock tube studies were also examined by testing in pure N2 and deliberate addition of air to the CH4N2 mixtures. The test campaign measured radiation at velocities from 4.7 kms to 8 kms and free-stream pressures from 0.1 to 0.47 Torr. These conditions cover a range of potential trajectories for flight missions, including a direct ballistic trajectory, a fly by or an extremely high speed entry. Radiances measured in this work are substantially larger compared to that reported both in past EAST test campaigns and other shock tube facilities. Depending on the metric used for comparison, the discrepancy can be as high as an order of magnitude. Potential causes for the discrepancy, such as the effect of oxygen due to Air leakage, gas composition and purity are discussed. The present work provides a new benchmark set of data to replace those published in previous studies.

Brandis, A. M↗
NASA NTRS1971

Approximate optimal atmospheric entry trajectories

Reentry glider approximate optimal atmospheric entry trajectories for maximizing function of terminal velocity, altitude, flight path and heading angle under terminal nonlinear constraints

Speyer, J. L.↗
NASA NTRS1993

Depletions of sulfur and/or zinc in IDPs: Are they reliable indicators of atmospheric entry heating?

The degree of heating of interplanetary dust particles (IDP's) on Earth atmospheric entry is important in distinguishing cometary particles from main-belt asteroidal particles. Depletions in the volatile elements S and Zn were proposed as chemical indicators of significant entry heating. The S and Zn contents of cosmic dust particles were correlated with physical indicators of atmospheric entry heating, such as the production of magnetite and the loss of solar wind implanted He. The results indicate that the Zn content of IDP's is a useful indicator of entry heating, but the S content seems to be less useful.

Flynn, G. J.↗
NASA NTRS1990

Computation of thermo-chemical nonequilibrium Martian atmospheric entry flows

The aerothermodynamics of a Martian atmospheric entry trajectory are studied. A chemical kinetics model for the CO2-N2 mixture found in the Martian atmosphere is implemented in a two-dimensional computational fluid dynamics method. The gas mixture is allowed to be in thermo-chemical nonequilibrium and to be composed of eight species characterized by two temperatures. The CO2 reaction model is validated by comparing computations to experimental results. Results for typical Martian entry conditions are presented and limitations of the current thermophysical model are discussed.

Candler, Graham V.↗
NASA NTRS1992

Atmospheric entry survival of large micrometeorites: Implications for their sources and for the cometary contribution to the zodiacal cloud

Atmospheric entry heating simulations indicate that a large fraction of the micrometeorites larger than 100 microns in diameter which survive atmospheric entry must have entered the Earth's atmosphere with velocities very near the Earth's escape velocity. Thus, these particles must have been captured by Earth from heliocentric orbits with small eccentricities and low inclinations, indicating a main-belt asteroidal source. Space exposure ages measured on these large micrometeorites are also consistent with a main-belt asteroidal source. However, dynamical calculations have previously indicated that particles larger than 100 microns in diameter were likely to be destroyed by catastrophic collisions in the time required for orbital evolution from the main-belt to Earth capture by Poynting-Robertson drag. The absence of a large amount of collisional debris in the less than 50 microns size range indicates these large micrometeorites are not the few, rare survivors of a mostly collisionally disrupted population. The measured space exposure ages, which are about an order of magnitude larger than their calculated catastrophic collision lifetimes, confirm the survival of these large micrometeorites for times much longer than the calculated catastrophic collision lifetimes. Since collisions with cometary dust less than 20 microns in size were expected to be the major contributor to the collisional destruction of these larger particles, the contribution of cometary material to the zodiacal cloud is likely to be much smaller than previously believed.

Flynn, George J.↗