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Craig, R. A.

Publications and source records attributed to Craig, R. A..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Proposed radiometric measurement of the wake of a blunt aerobrake

This paper describes the aerothermal environment in the afterbody region of a blunt entry body. Recent ground-based experiments and computational predictions of the afterbody flow structure and radiation are presented. The similarity between the flowfield structures observed in the ground-based experiments and that obtained by calculation is encouraging. Approximate calculations of the radiative heating rate to the base are presented. Many of the phenomena associated with the expanding flow at the corner and the formation of the wake neck, however, are not well understood and require further study. A flight experiment is described that would use spectral and total measurements of the wake radiation as a nonintrusive diagnostic method to provide insight into the thermodynamic state of the wake gas.

Strawa, A. W.↗
NASA NTRS1991

The NASA spring 1984 stratosphere-troposphere exchange experiment - Science objectives and operations

The first experiment of the Stratosphere-Troposphere Exchange Project to identify modes of transport during large-scale cyclogenesis is reviewed. The U-2 aircraft instrument payload is described and the flight paths are shown in relation to their meteorological situations. The procedures used to predict large-scale cyclogenesis and associated tropopause folding and to direct the aircraft are reviewed.

Russell, P. B.↗
NASA NTRS1991

Radiometric investigation of the wake flow of the forthcoming Aeroassist Flight Experiment

This paper describes the rationale for conducting the proposed radiation measurement in the afterbody region of the Aeroassist Flight Experiment (AFE) vehicle, the results of the calculations of expected radiation intensities performed to date, and the instrumentation for the measurement. The experiment, named the Afterbody Radiometry Experiment (ARE), is one of the experiments that will be carried on board the AFE vehicle. The paper collates the existing experimental data to show the possibility that there may be substantial radiative heating of the afterbody region of an Aeroassisted Space Transfer Vehicle, which necessitates an experiment of the kind proposed. Calculations of the radiative heating rate to the base of the AFE are, qualitatively, in fair agreement with previous experimental work, which indicated that the radiative heating of the base is about 5 percent of that at the stagnation point.

Strawa, A. W.↗
NASA NTRS1990

The Importance of the Measurement of the Unsteady Wake of the Aeroassist Flight Experiment Vehicle: A White Paper

The High Frequency Radiometer (HFR) is the only instrument on the Aeroassist Flight Experiment (AFE) with sufficient temporal resolution to discern the frequency of unsteady wake oscillations. Determining both the frequency and amplitude of wake unsteadiness during AFE atmospheric entry is essential for reliably predicting the geometry and motion of the wake of future Aeroassisted Space Transfer Vehicles (ASTV). These parameters directly affect the location and size of the pay- load and the weight of the required afterbody heat protection. The purpose of the AFE is to validate the technologies required for the design of ASTVs, which will be used to exploit Earth-lunar space. This validation will be conducted at a combination of vehicle size, altitude, and velocity not obtainable in ground-based facilities. The AFE will provide the experimental flight data needed to improve our understanding of hypersonic-wake physics and to validate computational predictions of the aerodynamic and heating loads, including afterbody radiative heating loads, on an ASTV. Reliable prediction of ASTV wake flows will ensure that payloads are located within the shear-layer envelope and will determine the amount of thermal protection the payloads require. Specifically, understanding the temporal nature of the wake unsteadiness is important for two reasons. Most importantly, analysis of ground-based experiments suggests that wake unsteadiness results in a variation of as much as +/- 5 deg in the shear-flow turning angle. This angle must be reliably predicted to avoid shear-layer impingement on the vehicle afterbody, which would result in heating rates of about 10 W/sq cm, of the same order as on the forebody stagnation point. Secondly, the energy associated with wake unsteadiness will reduce the static enthalpy of the wake fluid and cause an error of as much as 30% in the amount of predicted wake radiative heating. Therefore, the HFR flight data, which will quantify the frequency and amplitude of the wake unsteadiness, are required for the verification of computational models of ASTV flowfields. Measurement of wake unsteadiness has been endorsed by the Peer Science Steering Group and the AFE Computational Fluid Dynamics (CFD) Working Group. The Peer Science Steering Group has stressed that a reliable measurement of the wake unsteadiness is fundamental because incorporating unsteadiness represents a substantial challenge to the CFD community, and a reliable measurement will raise confidence in the computer simulation. The AFE CFD Working Group has stated that 44 any data which would prove the existence and effects of unsteady flow would be extremely valuable.

Strawa, A. W.↗
NASA NTRS1985

The Pioneer Venus extended mission

A history of the Pioneer Venus Orbiter is given, as well as a presentation of the ongoing and future missions (through reentry in 1992). General characteristics of Venus including atmospheric and ionospheric data are reviewed. Development of the Pioneer program and studies including comet detection, gamma ray bursts, composition and structure of the atmosphere, ionosphere, clouds, and solar wind are discussed. Planned observations of Halley's Comet in 1986 and of past observations of the Comet Enke are examined in detail. Maps and diagrams illustrate the studies and observations of this extended mission. Specification of the spacecraft as well as details of its orbits are given.

Craig, R. A.↗
NASA NTRS1984

Pioneer to Venus - The multiprobe and orbiter missions

The missions of the Pioneer multiprobe and orbiter spacecraft to Venus are surveyed and illustrated with drawings, photographs, maps, and diagrams. The general characteristics of Venus and the pre-Pioneer missions are reviewed; the developmental history of the Pioneer project is traced; the spacecraft and their orbits and deployment are described; and the scientific findings on the planet surface, atmosphere, and ionosphere are summarized. The experiments planned for the extended mission of the orbiter (through reentry in 1992) are briefly characterized, includidng solar-wind-interaction studies, comet detection, ionosphere and aeronomy investigations, global lightning survey, optical observations, gamma-ray-burst detection, radar mapping, gravity measurements, and observations of Halley's Comet during February, 1986.

Craig, R. A.↗
NASA NTRS1983

Sulfur trioxide in the lower atmosphere of Venus

Inconsistencies and ambiguities are noted by the present consideration of Pioneer Venus and Venera atmospheric composition measurement of Venus in the context of lower atmosphere thermodynamic equilibrium. Among the scenarios projected on the basis of assumed correctness for selected data subsets, the O2 and SO2 concentrations reported by the Pioneer Venus chromatograph and the H2O concentrations reported by Venera 11 suggest that large concentrations of SO3 are present in the lower atmosphere of Venus. Such SO3 concentrations lead, however, to difficulties in explaining the atmosphere at and above the cloud tops, and in addition require specific assumptions concerning chemical reaction rates at and near the surface.

Craig, R. A.↗
NASA NTRS1982

Staged Turbojet Engine Would Emit Less NO

New turbojet-engine concept could reduce nitric oxide emissions to a level from one-fifteenth to as little as one three-hundredth that of conventional units. Multiple-stage combustor could overcome flame instability problems associated with previous low-flame-temperature systems. It operates in a relatively-simple adiabatic mode without elaborate fuel-flow and air circulation patterns.,

Craig, R. A.↗
NASA NTRS1980

Pioneer Venus gas chromatography of the lower atmosphere of Venus

A gas chromatograph mounted in the Pioneer Venus sounder probe measured the chemical composition of the atmosphere of Venus at three altitudes. Ne, N2, O2, Ar, CO, H2O, SO2, and CO2 were measured, and upper limits set for H2, COS, H2S, CH4, Kr, N2O, C2H4, C2H6, and C3H8. Simulation studies have provided indirect evidence for sulfuric acid-like droplets and support the possibility of water vapor at altitudes of 42 and 24 km. The paper discusses the implications of these results for the origin, evolution, and present state of Venus' atmosphere.

Oyama, V. I.↗
NASA NTRS1980

Measurements of NO, O3, and temperature at 19.8 km during the total solar eclipse of 26 February 1979

Local measurements of stratospheric NO and O3 mixing ratios and air temperature were made during the total solar eclipse of 26 February 1979. The instrumentation was carried aboard a U-2 aircraft flown at an altitude of 19.8 km in the region near 47 deg N, 112 deg W. Eclipse maximum occurred approximately in the middle of the 2-3/4-hr measurement period. The NO mixing ratio was reduced at least a factor of 25 at the maximum of the eclipse. The decrease and recovery of NO during the passage of the Moon's shadow over the measurement region follows approximately the predictions of two independent models. No change was observed in either the O3 mixing ratio or the air temperature that could be attributed to the eclipse.

Starr, W. L.↗
NASA NTRS1980

Reduction of nitric oxide emissions from a combustor

A turbojet combustor and method for controlling nitric oxide emissions by employing successive combustion zones is described. After combustion of an initial portion of the fuel in a primary combustion zone, the combustion products of the primary zone are combined with the remaining portion of fuel and additional plenum air and burned in a secondary combustion zone under conditions that result in low nitric oxide emissions. Low nitric oxide emissions are achieved by a novel turbojet combustor arrangement which provides flame stability by allowing stable combustion to be accompanied by low nitric oxide emissions resulting from controlled fuel-lean combustion (ignited by the emission products from the primary zone) in a secondary combustion zone at a lower combustion temperature resulting in low emission of nitric oxide.

Craig, R. A.↗
NASA NTRS1980

Sounding the stratosphere and mesosphere by infrared limb scanning from space

Inversion of the measurements obtained by the infrared limb scanner on the Nimbus 6 satellite has demonstrated that the stratospheric and mesospheric temperatures and ozone concentrations may be obtained remotely from space with accuracy and precision comparable to in situ methods. Such global data have many applications in middle atmospheric research and operational temperature sounding.

Gille, J. C.↗
NASA NTRS1979

Measurement of NO and O3 from aircraft: 1977 tropical convergence zone experiment

As part of the Ames Research Center program to explore the nature of stratosphere-troposphere exchange processes occurring in the Intertropical Convergence Zone, simultaneous in situ measurements of nitric oxide and ozone mixing ratios were made with the Ames stratospheric air sampler SAS 2. The SAS 2 is a second-generation system; it employs four parallel sensors and was designed primarily for measurements at altitudes of 60,000 ft and above on the U-2 stratospheric research aircraft. The only modifications required for this study was the addition of an air sample flow restrictor. Data were obtained with the SAS 2 system on July 26, 27, 30 and 31, 1977. Generally, 30-min measurements were made at each of six altitudes ranging from 45,000 ft to 70,000 ft, and separated by 5,000 ft intervals.

Starr, W. L.↗
NASA NTRS1976

Holographic Recording Materials Development

Organic photorefractive materials were evaluated for application in a reversible holographic memory system. Representative indigo and thioindigo derivatives and several stilbene derivatives were studied as well as 15, 16-dialkyldihydropyrene derivatives the following goals were achieved: (1) the successful writing of phase holograms in a thioindigo/polymer gel system, (2) the successful writing and erasing of phase holograms in a variety of indigo/polymer gel and indigo/solid polymer systems, and (3) the identification of indigoid dyes and 15, 16-dialkyldihydropyrene derivatives as materials potentially suitable for utilization in an operational system. Photochemical studies of the stilbene, indigo, thioindigo, and dialkyldihydropyrene derivatives in solution and in a variety of polymer matrix materials were conducted with the goal of optimizing the photorefractive behavior of the chemical system as a whole. The spectroscopic properties required of optimal photorefractive materials were identified, and it was shown that both the indigoid dyes and the dialkyldihydropyrenes closely match the required properties.

Verber, C. M.↗