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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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All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Characterization of Titan Entry Radiative Heating in the Low Density Electric Arc Shock Tube

Prediction of aftbody radiative heating for Dragonfly’s entry at Titan requires accurate models to inform the design of its thermal protection systems. Previously reported investigations of shock layer aftbody radiation in the Electric Arc Shock Tube (EAST) at NASA Ames Research Center focused on the lower altitude/higher density part of the trajectory. This paper presents the first optical emission spectroscopy measurements of an ongoing test series in the new aluminum Low Density Shock Tube (LDST), recently installed at EAST, focusing on the radiative heating characterization through the higher altitude portion of Dragonfly’s entry path. Experimental data collected at a fill pressure of 0.1 Torr and shock velocities between 5.2 and 6.2 km/s show favorable agreement to similar conditions previously tested in the 4" High-Velocity Shock Tube, as well as improvements in the signal to noise ratio and available test time. Simulations employing DPLR and NEQAIR underpredict the experimental radiance, with increasing discrepancy from the NIR towards the UV wavelength range, thus motivating further efforts in improving the current non-Boltzmann model for the CN molecule.

A Fagnani↗
NASA NTRS1972

Evaluation of a self-aspirating local total enthalpy probe in a low-density arc-heated hypersonic wind tunnel

A shock-swallowing, self-aspirating, local total enthalpy probe has been evaluated in a low density nonequilibrium, hypervelocity airstream. The probe, which incorporated an air gap to separate the internal and external cooling passages, was tested in an electric archeated wind tunnel at an average Mach number of 11.7 and an average Reynolds number per meter of 57,000. The free stream enthalpy probe data are compared with bulk calorimeter measurements of total enthalpy at the beginning of the gas expansion and with local total enthalpy inferred from a theoretical nonequilibrium gas expansion model by using free stream velocity measurements obtained from a mass flow probe. The three techniques are in relative agreement at the lower enthalpies. However, at the higher enthalpies, the enthalpy probe data lie considerably below the other data. This low data may be caused by the chemical and vibrational energy frozen in the flow not being sensed by the probe. Other problems associated with the shock-swallowing total enthalpy probe are discussed, and recommendations for improving the probe performance are presented.

Guy, R. W.↗
NASA NTRS1990

Survey of measurements of flow properties in arc jets

This paper reviews techniques for determining flow properties in low density arc jets used for materials and structures testing. Properties measured include flow total enthalpy, pressures, heat fluxes, static temperatures, electron density, species concentrations, and flow velocity. The probe techniques covered are pressure, heat flux, electrostatic, and mass sampling. Nonintrusive techniques include emission spectroscopy, laser-induced fluorescence, laser Thomson scattering, and Raman scattering. It is concluded that several techniques must be used in a single facility to obtain all of the flow field properties necessary to predict heat fluxes in a nonequilibrium expansion.

Scott, Carl D.↗
NASA NTRS2012

Negative Ion Chemistry in the Coma of Comet 1P/Halley

Negative ions (anions) were identified in the coma of comet 1P/Halley from in-situ measurements performed by the Giotto spacecraft in 1986. These anions were detected with masses in the range 7-110 amu, but with insufficient mass resolution to permit unambiguous identification. We present details of a new chemical-hydrodynamic model for the coma of comet Halley that includes - for the first time - atomic and molecular anions, in addition to a comprehensive hydrocarbon chemistry. Anion number densities arc calculated as a function of radius in the coma, and compared with the Giotto results. Important anion production mechanisms arc found to include radiative electron attachment, polar photodissociation, dissociative electron attachment, and proton transfer. The polyyne anions C4H(-) and C6H(-) arc found to be likely candidates to explain the Giotto anion mass spectrum in the range 49-73 amu. Thc CN(-) anion probably makes a significant contribution to the mass spectrum at 26 amu. Larger carbon-chain anions such as C8H(1) can explain the peak near 100 amu provided there is a source of large carbon-chain-bearing molecules from the cometary nucleus.

Cordiner, M. A.↗
NASA NTRS1996

Electromagnetic radiation generated by arcing in low density plasma

An unavoidable step in the process of space exploration is to use high-power, very large spacecraft launched into Earth orbit. Obviously, the spacecraft will need powerful energy sources. Previous experience has shown that electrical discharges occur on the surfaces of a high-voltage array, and these discharges (arcs) are undesirable in many respects. Moreover, any high voltage conductor will interact with the surrounding plasma, and that interaction may result in electrical discharges between the conductor and plasma (or between two conductors with different potentials, for example, during docking and extravehicular activity). One very important aspect is the generation of electromagnetic radiation by arcing. To prevent the negative influence of electromagnetic noise on the operation of spacecraft systems, it seems necessary to determine the spectra and absolute levels of the radiation, and to determine limitations on the solar array bias voltage that depend on the parameters of LEO plasma and the technical requirements of the spacecraft equipment. This report describes the results of an experimental study and computer simulation of the electromagnetic radiation generated by arcing on spacecraft surfaces. A large set of high quality data was obtained during the Solar Array Module Plasma Interaction Experiment (SAMPIE, flight STS-62) and ground test. These data include the amplitudes of current, pulse forms, duration of each arc, and spectra of plasma waves. A theoretical explanation of the observed features is presented in this report too. The elaborated model allows us to determine the parameters of the electromagnetic noise for different frequency ranges, distances from the arcing site, and distinct kinds of plasma waves.

Vayner, Boris V.↗
NASA NTRS1975

Electron density decrease in SAR arcs resulting from vibrationally excited nitrogen

A study is made of the effect on theoretical electron-density profiles of vibrational enhancement in the rate of the reaction O(+) + N2 yields NO(+) + N. It is shown that the F-region electron-density depression that is observed in stable auroral red (SAR) arcs may be caused by vibrational excitation of molecular nitrogen.

Newton, G. P.↗
NASA NTRS2018

Evidence for Arcing on the International Space Station Solar Arrays

The International Space Station (ISS) is powered by a set of 160 V photovoltaic arrays (PVA) in the US sector. Arcing thresholds for the ISS PVAs measured in the laboratory are shown to vary from -210 V to -457 V depending on the ambient plasma density, where low arcing threshold occurs at high plasma densities. Arcing of ISS PVAs on-orbit is unlikely under normal operating conditions. The net potential of a solar cell relative to space depends on the position of the cell within a string, the (vxB)•L contribution to the potential at the location of the cell, and the frame potential of ISS due to solar array charging. Net potentials on a cell will reach the arcing threshold only on rare occasions. However, the situation changes when damaged PVA strings are considered. Open circuit strings can exhibit voltages exceeding -300 V when the strings are shunted. Under these conditions the local potential on the damaged string can easily exceed arcing thresholds at the low end of the -210 V to -457 V range for ISS PVAs. Because arcing to space on the array will remove some fraction of the net negative charge on the ISS, transient variations in the frame potential are expected during the electrostatic discharge events. We report a new class of transient ISS frame potential variations consistent with arcing on open strings using data from the ISS Floating Potential Measurement Unit’s Floating Potential Probe instrument.

Minow, Joseph I.↗
NASA NTRS1974

An experimental and analytical study of slip and catalytic boundary conditions applied to spheres in low Reynolds number arc jet flows

Measurements of low-density dissociated arc-heated flows around low and high surface catalycity spheres are compared with numerical solutions to the full Navier-Stokes equations for reacting gas flow fields, taking into account slip and finite surface catalytic boundary conditions. A time-dependent finite difference solution technique developed by Li (1973, 1974) is used in the investigation and a simple transport model is employed for the flows considered. The correctness of the solution approach is demonstrated by the very good agreement obtained between experimental and computational data.

Scott, C. D.↗